News and Events

Organic gardening advice

08-May-2013

During our Wellness Weeks, we host organic gardening classes to help guests better understand how to grow chemical free produce at home. The notes below share some of our expertise on organic principles and practices, building a garden, soil improvement and composting, climate zones, successional planting, seeds and seedlings, and pest and disease control.

Organic principles and practices

Organic gardening attempts to mimic nature. Ecosystems have a complex and sometimes predictable set of processes that can be guided, manipulated and reproduced in a garden setting. Some examples include energy systems (i.e. moisture, temperature and soil fertility), food systems (i.e. small organisms being consumed by larger organisms) and reproductive systems (i.e. plants and insects responding to environmental conditions in order to reproduce).

Ecosystems are most predictable when they are balanced and stable. A balanced ecosystem can naturally regenerate a disturbed area without changing the characteristics of the ecosystem. This is the key principle that applies to organic gardening. In any garden, there should always be an area of new planting (i.e. a disturbed area) that is surrounded by a much larger area of existing plants (i.e. a stable area). The stable area provides a range of environmental services, including a moderated micro-climate and habitat for beneficial insects, which provide some protection to young plants in the disturbed area.

In practice, an organic garden requires a diverse range of vegetable and flower species and a diverse range of age groups (i.e. seedlings through to mature plants that have gone to seed) and plant structure (i.e. small plants, tall plants, bushy plants and flowering plants). Such diversity mimics natural ecosystems. It is also important for plants to be healthy and growing in optimal soil and climate conditions, as sick plants attract more pests and diseases than healthy plants. They are also less productive. Over watered and over fertilised plants are just as prone to pest and disease problems as under watered and under fertilised plants.

Garden size is also important. A small 2m2 garden will have less resilience to disturbance than a 20m2 garden. Small gardens can still be organic, however more reliance will be placed on organic interventions such as pyrethrum or oil sprays, as opposed to biological control from stable garden areas.

Gardening success is generally dependent on natural processes. In some cases, management interventions such as water from a tap, fertilisers from a bag and pest control from a spray bottle can offset natural processes. In other cases, they can not. Extreme rainfall events, gale force winds, early or late frosts, and extreme heat can destroy a garden in minutes! 

Good organic gardeners understand, accept and plan for unexpected events and seasonal variability through simple risk management. This involves the use of multiple varieties of vegetables and flowers planted at regular intervals. Good organic gardeners are also prepared to accept a percentage of crop loss (i.e. the better the gardener the lower percentage) and plant excess quantities to cover any unexpected losses.

Building an Organic Vegetable Garden: Step-by-step Instructions

Garden Construction and equipment

The vast majority of Australian soils have very low levels of organic matter in the topsoil and high levels of clay in the subsoil. This results in poorly drained and infertile soils. While it's possible to improve soils with various conditioning agents such as compost, manure, gypsum and lime, it takes a long time and results can be disappointing. For this reason, people have been growing vegetables in raised garden beds since colonial days. A raised garden bed allows you to control important soil properties such as fertility and drainage. The money you invest in raised garden beds and compost will be rewarded with healthy and productive vegetable gardens.

Building a Raised Garden Bed

Use timber, steel or plastic garden beds – there are plenty of products available!

Filling a Raised Garden Bed - Compost Garden

Organic compost is best made in the garden bed by mixing lucerne hay and chicken manure. It only takes two weeks of 'hot composting' before you plant your first seedlings. Organic compost is also the most water-efficient planting medium. Good compost absorbs moisture like a sponge and requires minimal watering (i.e. twice a week in summer and once a week in winter, under average conditions). Organic compost is the best option for raised garden beds on soft ground. It costs $30-$40 per square metre.

Step 1: Add a 10cm thick layer of lucerne hay. This provides the carbon content of the compost.

Step 2: Add a 5cm thick layer of composted or pelletised chicken manure. This provides the nitrogen content of the compost.

Step 3: Mix the lucerne hay and chicken manure and wet the layer thoroughly.

Step 4: Add a 15cm thick layer of organic sugar cane mulch (or another type of straw) and wet the layer thoroughly. Leave the compost mix for two weeks to complete the ‘hot’ composting process. 

Step 5: After two weeks, create a 10cm wide and 10cm deep hole in the mulch layer and fill with organic potting mix, garden mix, topsoil or compost.

Step 6: Plant one seedling into the topsoil and spread a small handful of slow release organic fertiliser on the mulch around the seedling.

Step 7: After 6 months or two crop rotations, the lucerne hay and chicken manure will form rich compost and reduce in volume by 50 percent. Simply repeat Steps 1-6 to continue building your soil volume. After 12 months and two compost mixes, your garden will have 25cm of rich compost soil. From this point, you only need to add composted cow manure or pelletised organic fertiliser (NPK ratio of 4:3:2) every 6 weeks to maintain productive crop growth.

Filling a Raised Garden Bed - Soil Garden

Potting mix and garden mix are manufactured planting mediums that mix, among other things, sawdust, pine bark, fertilisers, manure, and moisture absorbing agents. Most are manufactured according to various Australian Standards. Potting mix and garden mix are not organic growing mediums. They are best used in raised garden beds on hard ground, in combination with an underlayer of permeable fabric, to prevent drainage marks on tiles, concrete or pavers.

Step 1: Add a 25cm layer of organic potting mix, garden mix, topsoil or compost.

Step 2: Add a 5cm thick layer of organic sugar cane mulch (or another type of straw).

Step 3: Create a 10cm wide and 10cm deep hole in the mulch layer and fill with organic potting mix, garden mix, topsoil or compost.

Step 4: Plant one seedling into the topsoil and spread a small handful of slow release organic fertiliser on the mulch around the seedling.

Building a Garden Guard

A simple Garden Guard will protect your vegetables from birds, possums, cats, dogs, wind, hail, frost and the hot summer sun. The Garden Guard can be covered with bird netting, shade cloth, clear plastic or any other sheeting depending on your particular needs for each season. Each of the following components can be purchased at hardware shops.

Step 1: For soft ground, insert the 50cm rods 5cm into the ground and leave 15cm sticking out of the top garden bed.

Step 2: Insert a 2m length of 15mm diameter Vinidex PVC Pressure Pipe over each rod to form a tunnel frame over the garden bed. 

Step 3: Clamp the PVC Pressure Pipe to each rod with a 15-20mm Boston Steel Hose Clamp.

Step 4: Cover the PVC Pressure Pipe frame with your required sheeting (i.e. bird netting, shade cloth or clear plastic).

Step 5: Trim the sheeting to leave about 30cm flat on the ground at the base of the garden bed.

Step 6: Lay star pickets (or something flat and heavy) over the sheeting to attach it to the ground.

Garden Equipment

It’s easy to be overwhelmed by the products available at garden centres and hardware shops, but you really don’t need that much equipment to manage an organic vegetable garden. The following is a list of essential equipment.

1. Seedling punnets. You can buy these in kits or just reuse the ones you buy seedlings in. It’s best to use the 6 cell containers since they are easy to manage and replace. We often buy Oasis seedlings and reuse the blue cell containers.

2. Seedling water trays. Just buy a rectangular pot tray and drill holes through the sides. This prevents the seedlings from drying out or absorbing too much water. Seedling punnets are easy to move around when sitting on a water tray.

3. Seedling cover. You can buy a plastic cover as part of a seed raising kit, but we’ve never had much success with solid plastic covers. Our preference is to use a 30cm by 50cm plastic container, remove the base and cover the hole with 22% white shade cloth. This provides a perfect micro-climate for germination of seeds and growth of seedlings.

4. Watering can. A 10L watering can is best so you can correctly mix concentrated plant conditioning liquids such and Seasol and Powerfeed.

5. Spray bottles. It’s worth buying two 1L bottles for seedling sprays and pest control sprays and one 5L bottle for Bordeaux Spray.

6. Garden Scissors for pruning.

7. Wire mesh. We use 1.2m wide square wire mesh to make trellises for tomatoes and cucumbers. Cut a 1m length, roll it into a cylinder and join the edges with plastic cable ties. 

Soil Improvement and Composting

The majority of Australian soils have very low levels of organic matter. This is a major constraint to plant growth as organic matter provides most of the fertility, biological activity and moisture retention in the topsoil. It is possible to improve soils with various conditioning agents such as artificial fertilisers, compost, manure, green manure, gypsum and lime, however, it takes a long time and results can be disappointing due to high rates of leaching.

The most productive soils for organic vegetable gardens are those rich in organic matter and the best way to achieve this is through composting and green manuring. You can either build compost gardens from lucerne hay and chicken manure (as above), or you can make separate piles of compost and add it to the garden when required. We do both. The later is a great way to incorporate your kitchen scraps and garden clippings into the composting process without adding disease or seeds.

Step 1: Stockpile your kitchen and garden scraps in a possum proof enclosure. A compost bin works well, as does an enclosure of chicken wire.

Step 2: Combine 33% lucerne hay, 33% chicken manure and 33% kitchen scraps in alternate layers to create a one cubic meter compost mound. Other combinations include 70% lucerne hay and 30% chicken manure or 50% lucerne hay and 50% cow manure. Mix and wet each layer thoroughly as you increase the size of the compost mound.

Step 3: Cover the compost mound with a 10-15cm thick layer of sugar cane mulch to provide insulation.

Step 4: Keep the mound moist for the next four months by watering it for 10 minutes twice a week in warmer months and once a week in cooler months.

Climate zones

Each plant has a genetically programmed response to environmental conditions (i.e. rainfall, humidity, temperature, sunlight, day length and soil fertility). When conditions are optimum, plant growth is most productive. When conditions are sub-optimal, plant growth is constrained. For example, too much moisture or too little moisture can constrain and eventually kill a plant. This is the case for all environmental conditions.

Given the strong influence of latitude and altitude on environmental conditions, it's possible to classify rainfall, humidity, temperature, sunlight and day length into climate zones. Each climate zone has a relatively homogenous set of environmental conditions. This, in turn, means that plant growth and management is relatively homogenous within each climate zone, but can vary significantly between climate zones – even adjacent ones. For example, Penrith in western Sydney and Leura in the Blue Mountains of NSW are only 50km apart but have drastically different climates. In this case, an altitude difference of 900m means that Leura is colder, wetter and cloudier than Penrith.

Successional Planting

The ideal vegetable garden produces a continual supply of fresh vegetables and herbs. This requires frequent planting of seedlings to replace the plants that have been harvested. Gardeners can make the mistake of planting too many seedlings at once and end up with excess vegetables followed by an empty garden. The problem is easy to solve with successional planting.

All vegetable species (i.e. lettuce, tomato, spinach, corn) have multiple varieties that evolved in different parts of the world and have more recently been bred for particular characteristics. Breeding techniques range from selection of individual plants with unique qualities (i.e. disease resistance, superior flavour and extended cropping period) to complex genetic engineering. Commercial plant varieties are often bred for a broader range of qualities (i.e. shape, colour, longevity and yield). Varieties are mostly labelled as ‘heirloom’ or ‘improved’ depending on the level of breeding.

Most vegetable varieties reach maturity within 8-14 weeks of germination. The most productive gardens are those where the requirements of each variety match the climate conditions during the growth period. This requires suitable conditions for the entire life cycle of the plant (i.e. correct soil temperature for seed germination, suitable climate conditions for plant growth, and suitable climate conditions for vegetable formation).

Some vegetables perform well over a range of seasons (i.e. loose-leaf lettuce varieties), while others are more limited (i.e. pea varieties). Some vegetables have varieties that perform well in different seasons, while others have varieties that perform well in different parts of the same season. A productive successional garden uses multiple varieties to ensure that plants are always growing in optimal conditions. It’s common to use 3-5 varieties of tomato, lettuce, bean or broccoli over a year to ensure maximum production.

In practice, successional planting requires regular planting every four weeks. Since each harvest period will extend for four weeks, it’s best to grow vegetables that can be harvested multiple times from the same plant. Examples include tomatoes, cucumber, zucchini, loose leaf lettuces, broccoli, spinach and most annual herbs. Gardens based on ‘cut and come again’ harvesting are the most efficient way to use limited space.

A practical garden size is 10 square metres, based on 2.5 square metres of planting every four weeks. Most vegetables require 25cm spacing which allows an average density of 16 plants per square metre, or 40 plants per planting. Larger plants such as tomatoes, cucumbers, zucchini, potatoes and corn require 30-50cm spacing. In between the vegetables and herbs, you should also plant annual flowers at a density of one annual flower plant per five vegetable plants. This adds to the diversity of plants (species, flowers, colours and structure), which is needed for a successful organic garden.

Smaller gardens require smaller areas of monthly planting. For example, a six square metre garden would be based on 1.5 square metres of planting (24 plants on average) every four weeks, while a three square metre garden would be based on 0.75 square metres of planting (12 plants on average) every four weeks. Remember that the smaller the area of garden, the sooner your monthly harvest will expire.

Seeds and Seedlings

Commercial seedlings are easy to source, easy to plant and relatively cheap. However, the minimum purchase size is usually 6 seedlings, which can be too many for successional planting. Also, the choice of plant variety is extremely limited and often not labelled, which means you don’t know what variety you’re growing and thus can’t assess its performance in your garden.

The best way to control the number, variety and quality of your seedlings is to grow them from seed. There are numerous seed suppliers in Australia and some have excellent online shops to help you select the best variety for each climate zone and season. The suppliers we use regularly are Eden Seeds, New Gippsland Seeds, Diggers Club, Cornucopia Seeds, Green Patch Seeds, and Green Harvest. Green Harvest and Green Patch are best for QLD and Northern NSW gardens, while the remainder are best for Southern NSW, VIC, SA, WA and TAS.

Propagating seeds is delicate but not difficult. With the right equipment, good quality seed and correct seasonal plant selection, you can germinate seeds and raise seedlings with minimal time and effort.

Step 1: Fill seedling punnets to the required planting depth for each plant (as specified on the seed packet) with ‘seed raising mix’ from your local garden centre or hardware shop.

Step 2: Water the ‘seed raising mix’ until it’s moist. 

Step 3: Evenly spread 3 seeds on top of the ‘seed raising mix’ in each cell (except large seeds such as corn, peas and beans where you would only use one seed per cell). Some times germination rates are less than 100% so extra seeds in each cell ensure that at least one seed germinates per cell. Additional plants can be culled at a later time.

Step 4: Cover the seeds with ‘seed raising mix’ and ensure the depth of cover matches the instructions on the seed packet.

Step 5: Gently water the top layer of ‘seed raising mix’ with a fine spray bottle. Ensure that you don’t expose or dislodge the seed.

Step 6: Place the seedling punnets on a water tray.

Step 7: Depending on the season and your climate zone, either place the seedling punnets outside in a sheltered area (generally in spring, summer and autumn) or inside in a warm sunny area (generally in winter). You should move the seedling punnets indoors to protect them from extreme cold, heat, wind or rain.

Step 8: When placed outside, use a seedling cover to maintain an even micro-climate.

Step 9: Keep the ‘seed raising mix’ moist (but not wet) during the germination period (5-10 days for most plant varieties) and the early growth of stages.

Step 10: After 3 weeks from germination (or 4 weeks from planting), most seedlings will be 5-10cm high and ready for transplanting into the garden.

Step 11: Fill the water tray with a 50% dilution of Seasol or Maxicrop and soak the root bulbs overnight. This provides a quick nutrient fix to the seedlings and helps them survive the disturbance from transplanting.

Step 12: Gently squeeze the sides of each cell to separate the root bulb from the cell, and then remove the seedling with a forefinger and thumb grip at the base of each seedling (i.e. the thickest part of the stem). Another method is to scoop the root bulb out of each cell with a teaspoon.

Step 13: Plant the seedling into your soil, compost or potting mix and gently press around the base of the seedling to ensure good contact between the root bulb and soil.

Step 14: Cover the seedlings with a seedling cover for two weeks to help them adapt to the new garden conditions.

Step 15: After two weeks, remove the seedling cover and thin seedlings to one plant per spot (remember that you originally planted 3 seeds per cell and may have 3 plants per spot). This is best done by cutting the stems at ground level with scissors.

Sample Weekly Instructions for Sydney

Period: August Week 1

Climate Zone: Sydney

Garden Size: 10m2

Growing: lettuce, parsley, silver beet, broccoli, rocket, coriander, spinach, pea

Harvesting: lettuce, parsley, rocket, silver beet, spinach, coriander, broccoli

Instructions:

  1. Harvest and remove the remaining plants from the April rotation.
  1. Insert 3 trellises for pea plants at 30cm spacing.
  1. Plant seedlings from the July sowing - 4 spinach (Winter Giant or Winter Bloomsdale) at 25cm spacing, 12 pea (Sugar Snap Climbing or Snow Pea Oregon) at 4 plants per trellis, 6 lettuce (Cos Verdi or Rouge d’Hiver) at 25cm spacing, 4 coriander at 25cm spacing and 4 rocket (Cultivata or Astro) at 25cm spacing. Interplant 3 Marigold, 3 Sweet Alice and 3 Queen Anne’s Lace randomly among the vegetable seedlings. Also plant 6 seed potatoes (Desiree or King Edward) at 30 cm spacing – plant each potato 20cm below the top of the garden and cover with 5cm of soil or mulch.
  1. Apply Seasol (15ml/10L) to seedlings.
  1. Assist pea plants up the trellis by winding the tendrils around the wire.
  1. Check for caterpillars on all plants and remove by hand, or spray with pyrethrum if necessary.
  1. Check for aphids on all plants and spray with Pyrethrum if necessary.
  1. After harvesting the central broccoli stem, thin the mature leaves by 70% to encourage the growth of side shoots. Ensure side shoots are harvested before they flower to continue production.
Period: August Week 2

Climate Zone: Sydney

Garden Size: 10m2

Growing: lettuce, parsley, silver beet, broccoli, rocket, coriander, spinach, pea

Harvesting: lettuce, parsley, rocket, silver beet, spinach, coriander, broccoli

Instructions:

  1. Sow seeds for September planting - 4 tomato (Tommy Toe or Tigerella for tall plants or KY1 for dwarf plants), 12 cucumber (Revel, Green Gem or Burpless Hybrid), 6 zucchini (Black Beauty or Lebanese Hybrid), 4 basil (Sweet or Genovese), 6 bean (Gourmet Delight or Jade Stringless), 6 lettuce (Cos Verdi, Australian Yellow Leaf or Salad Bowl Green), 6 Marigold, 6 Cosmos, 6 Sweet Alice, and 6 Queen Anne’s Lace NOTE: Seedlings should be raised in a warm sunny position and protected from frost.
  1. Apply Seasol (30ml/10L) and Power Feed (40ml/10L) to all plants at a rate of 10L/2m2.
  1. Assist pea plants up the trellis by winding the tendrils around the wire.
  1. Check for caterpillars on all plants and remove by hand, or spray with pyrethrum if necessary.
  1. Check for aphids on all plants and spray with Pyrethrum if necessary.
  1. Harvest broccoli side shoots (before they flower) to continue production.
Period: August Week 3

Climate Zone: Sydney

Garden Size: 10m2

Growing: lettuce, parsley, silver beet, broccoli, rocket, coriander, spinach, pea

Harvesting: lettuce, parsley, rocket, silver beet, spinach, coriander, broccoli

Instructions:

  1. Order seeds for September planting – 8 seed potatoes (Desiree or King Edward from Diggers or your local garden centre).
  1. Assist pea plants up the trellis by winding the tendrils around the wire.
  1. Check for caterpillars on all plants and remove by hand, or spray with pyrethrum if necessary.
  1. Check for aphids on all plants and spray with Pyrethrum if necessary.
  1. Check for slugs and snails and remove be hand, or use Multiguard pellets if necessary. Note that these pellets are NOT organic, but they have no impact on other life forms.
  1. Harvest broccoli side shoots (before they flower) to continue production.

Period: August Week 4

Climate Zone: Sydney

Garden Size: 10m2

Growing: lettuce, parsley, silver beet, broccoli, rocket, coriander, spinach, pea

Harvesting: lettuce, parsley, rocket, silver beet, spinach, coriander, broccoli

Instructions:

  1. Apply Seasol (30ml/10L) and Power Feed (40ml/10L) to all plants at a rate of 10L/2m2. 
  1. Apply slow release organic fertiliser around all plants at a rate of 1 cup per square metre.
  1. Assist pea plants up the trellis by winding the tendrils around the wire.
  1. Check for caterpillars on all plants and remove by hand, or spray with pyrethrum if necessary.
  1. Check for aphids on all plants and spray with Pyrethrum if necessary.
  1. Harvest broccoli side shoots (before they flower) to continue production.
 

Pest and Disease Control

An organic garden is a small ecosystem with numerous life forms – bacteria, fungi, protozoa, insects, arachnids, annelids, nematodes, molluscs, chilopods, crustaceans, amphibians, reptiles, birds and mammals. A 10 square metre garden can have thousands of life forms, most of which you’ll never see!

Life forms that eat your plants are generally known as pests or ‘bad bugs’. Life forms that eat pests (or help with the soil building process) are generally known as ‘good bugs’. As much as we’d like to be rid of all ‘bad bugs’, the basic principles of ecology remind us that ‘good bugs’ would soon die of starvation if there were no ‘bad bugs’ to eat. So, to summarise thousands of pages of scientific research, a balanced and stable garden ecosystem needs ‘bad bugs’ and ‘good bugs’ – in the correct proportions. The trick is to manage the populations in a way that best suits the production of vegetables. This is done through general organic gardening practices and specific pest control practices.

General Practices

Maintain diversity. An organic garden requires a diverse range of vegetable and flower species and a diverse range of age groups (i.e. seedlings through to mature plants that have gone to seed) and plant structure (i.e. small plants, tall plants, bushy plants and flowering plants). Such diversity mimics natural ecosystems and provides a range of environmental services, including a moderated micro-climate and habitat for ‘good bugs’, birds and lizards.

Select the best varieties for seasonal and soil conditions. It’s important for plants to be healthy and growing in optimal soil and climate conditions, as sick or stressed plants attract more pests and diseases than healthy plants. They are also less productive. Over watered and over fertilised plants are just as prone to pest and disease problems as under watered and under fertilised plants.

Select pest and disease resistant varieties. Many heirloom and improved varieties have natural or bred resistance to pests and diseases. Most seed suppliers highlight such features on their websites and packaging.

Practice successional planting and crop rotation. Many vegetable species belong to the same plant families (e.g. Broccoli, Cabbage, Cauliflower, Brussels sprout, Kale and Turnip are all part of the Brassicaceae family, while Tomato, Capsicum, Eggplant and Potato are all part of the Solanaceae family).

Many pests and diseases are attracted to plants in the same family, and growing related plants in the same position over and over can lead to problematic pest and disease outbreaks. This can be minimised by rotating plants from different families through each planting position over time. An example is Snap Pea (Fabaceae) in winter, followed by Tomato (Solanaceae) in spring, followed by Celery (Apiaceae) in autumn, followed by Broccoli (Brassicaceae) in winter.

Add organic matter. The frequent addition of organic matter to the garden helps to break pest and disease cycles in a way similar to crop rotation. Properly made compost (see previous instructions), composted cow manure (purchased in bags from garden centres) and green manure (legume crops grown as part of your crop rotation) are all good sources of organic matter.

Use seaweed sprays regularly. Seasol and Maxicrop are both seaweed-based plant conditioning sprays that are amazingly effective at maintaining healthy and vigorous plants. We spray our plants every fortnight.

Remove underperforming plants. Plants can underperform for a variety of reasons. They may be the incorrect variety or suffer from unseasonal conditions. They may be overfertilised with nitrogen and attract sap sucking ‘bad bugs’ or overwatered and susceptible to root rot disease. They may be infected with fungal disease through improper handling or just be near the end of their life cycle. There are many possibilities. In any case, a sick plant is a magnet to pests and disease and can encourage large populations that upset the balance of the garden ecosystem. It’s good practice to remove all underperforming plants from the garden and put them through your next ‘hot compost’ (see instructions in Section 5). Don’t be sentimental about your plants. If they’re not producing, they have no place in your garden!

Avoid unnecessary handling. Many pests and diseases spread from plant to plant via you! Sap sucking insects and fungal diseases are good examples. One way to prevent the spread of pests and disease is to avoid all unnecessary handling of your plants. This includes brushing plants with your hands or legs when you walk past. Make sure that your garden layout includes enough space to walk between your garden beds.

Spend time in your garden. This is essential – the more time you spend in the garden, the more you’ll observe and the more you’ll learn. On a warm spring or summer morning, you’ll count dozens of life forms in your garden. Learn to identify them and watch what they do. Use an identification guide (The Garden Guardians by Jane Davenport is excellent) to help you distinguish between ‘bad bugs’ and ‘good bugs’. It’s also important to monitor ‘bad bugs’ and determine if they’re a problem or not. Sometimes they can be present in large numbers but not doing any serious damage. White fly is a good example - swarms can appear from under your zucchini or basil and make you run for the Pyrethrum bottle, but more often than not the damage is minimal.

Use broad spectrum organic insecticides only as a last resort. Pyrethrum is a great organic insecticide, but it kills ‘bad bugs’ and ‘good bugs’ indiscriminately. If you have an unacceptably large population of aphids or caterpillars that need to be removed, make sure you spray them at dawn or dusk when many of the ‘good bugs’ are not flying.

Manage risks. Good organic gardeners understand, accept and plan for unexpected events, seasonal variability and pest and disease damage through simple risk management. This involves the use of multiple varieties of vegetables and flowers planted at regular intervals. Good organic gardeners are also prepared to accept a percentage of crop loss (i.e. the better the gardener the lower percentage) and plant excess quantities to cover any unexpected losses.

Common Pest and Disease Control Practices

Ants have a symbiotic relationship with Aphids and encourage the growth of Aphid populations. Ants are best controlled by pouring boiling water down their nest holes.

Aphids are easily controlled with Pyrethrum spray or Eco-oil.

Bacterial diseases are best controlled with Bordeaux spray and prevented by the General Practices above. There are many recipes for Bordeaux spray – we use two teaspoons of Brickies Lime (from your local hardware shop) and one teaspoon of Copper sulphate (from your local garden centre or hardware shop) dissolved in one litre of water. A good trick is to enclose the Copper sulphate and Brickies lime in the foot of a stocking and add the stocking ‘ball’ to a two litre spray bottle with one litre of water. Shake the mixture until it’s dissolved and then remove the stocking ‘ball’. There’s always some Copper sulphate that doesn’t dissolve and will clog your spray nozzle unless you remove it in the stocking ‘ball’.

Birds are mostly beneficial in the garden as they devour all sorts of ‘bad bugs’. Sometimes, however, they can become pests. Parrots love green tomatoes in late summer and early autumn and young Magpies have great fun pulling seedlings out. It’s best to cover your garden with bird netting when birds become a problem.

Caterpillars and budworms are best removed by hand - look for their tiny droppings on the top of leaves and search upward for the culprit. Large infestations are easily controlled with Pyrethrum and Dipel.

Fruit flies are best controlled by placing permeable and breathable bags over immature fruit. Otherwise, Eco-naturale combines bait and organic insecticide with some success.

Fungal diseases are best controlled with Bordeaux spray and prevented by the General Practices above. See Bacterial diseases above for a Bordeaux spray recipe.

Mealy bugs are difficult to control, although Eco-oil has some success. We often just remove the affected parts of the plant (if possible) or, if the infestation is serious, remove the entire plant.

Mites are best controlled with Wettable Sulphur or Eco-oil.

Mildews are best controlled with Bordeaux spray. See Bacterial diseases above for a Bordeaux spray recipe. Increasing airflow and reducing overhead watering can also be effective.

Possums are a nuisance to most Australian gardeners and a major problem to some. They love most seedlings and have a particular taste for parsley, broccoli and lettuce. A hungry possum will eat most vegetables. A range of organic sprays made from garlic and chilli have mixed results in deterring possums. The safest method is to exclude them with bird netting over a structure such as a DIY ‘garden guard’.

Root nematodes are best controlled by crop rotation and the addition of organic matter.

Root rot is best controlled by improving drainage and limiting water. Incorporation of organic matter is the easiest method.

Scale are best controlled with Pyrethrum spray or Eco-oil.

Snails and slugs are best removed by hand at night (particularly after rain or watering). If populations are large, we use Multiguard snail pellets to protect seedlings. These aren’t organic, but are low impact - they only target snails and slugs and don’t affect other life forms.

Thrips are best controlled with Pyrethrum spray.

Vegetable bugs are best removed by hand.

White flies are best controlled with Pyrethrum spray. Overhead watering can also discourage them.

Potential Pest and Disease Problems for Preferred Plants

Basil can attract caterpillars and White fly. Both can be controlled with Pyrethrum spray.

Beans are relatively pest and disease free. Some varieties are susceptible to disease. Bean fly can be controlled with Pyrethrum spray.

Beetroot is relatively pest and disease free.

Broccoli is a favourite food source for White Cabbage Moth, which limits its productivity over summer months. Broccoli grown in autumn and winter has few pest and disease problems (other than hungry possums).

Celery is relatively pest and disease free.

Chilli is a common target for Fruit fly. Use permeable and breathable bags over immature fruit or spray with Eco-naturale.

Coriander is relatively pest and disease free.

Cucumber is susceptible to mite infestation in late summer and early autumn. Use Wettable Sulphur or Eco-oil as per directions. High humidity can lead to disease problems. Use Bordeaux spray on the underside of leaves – wait until the weather forecast is for three dry days with temperatures less than 30 degrees (Bordeaux spray in hot weather can burn plants).

Eggplant is a common target for Fruit Fly. Use permeable and breathable bags over immature fruit or spray with Eco-naturale. Use Bordeaux spray on the topside and underside of leaves to control fungal diseases - wait until the weather forecast is for three dry days with temperatures less than 30 degrees (Bordeaux spray in hot weather can burn plants).

Lettuce is relatively pest and disease free. Aphids can sometimes create problems.

Mizuna is relatively pest and disease free.

Parsley is relatively pest and disease free.

Pea is relatively pest and disease free. 

Potato is prone to a range of diseases. Make sure you purchase certified disease free seed potatoes to limit potential disease problems.

Rocket is relatively pest and disease free.

Silver beet is relatively pest and disease free.

Spinach is relatively pest and disease free.

Tomato is probably the most difficult plant to grow. Budworm in the fruit is best controlled by Dipel (although complete control is difficult) and Fruit fly is best controlled by permeable and breathable bags over immature fruit or Eco-naturale spray. Use Bordeaux spray on the topside and underside of leaves to control bacterial and fungal diseases - wait until the weather forecast is for three dry days with temperatures less than 30 degrees (Bordeaux spray in hot weather can burn plants).

With tomato, all of the General Practices above are critically important. Many gardeners still prune their tomato plants to a few strong leaders and remove the lower foliage. Our experience is that any kind of pruning encourages the spread of disease, which results poor yields. The alternative to pruning is wider spacing between plants (at least 70cm) so that the foliage of mature plants doesn’t overlap. This allows better air flow and reduced humidity – both of which are important to reduce the spread of disease. Also, it’s critically important not to water the tomato foliage as this encourages the spread of disease - just water the soil beneath the plant. The exception is seaweed sprays such as Seasol and Maxicrop every fortnight, which help to maintain healthy and vigorous plants.

Zucchini is prone to a range of fungal diseases in humid conditions. These can be controlled by limiting overhead watering – just water the soil beneath the plant. Half strength Bordeaux spray can also be used if necessary.

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