Eggplant

Start from seed: August-September

Optimum soil temperature for germination: 27-32⁰C

Plant seedlings: November-December

Plant spacing: 30 cm

Days to maturity: 50-120 days

Introduction 

Eggplant, also known as aubergine, belongs to the Solanaceae family, which also includes tomatoes, capsicums and chillies.

Eggplant was grown in India and China over 2500 years ago. From there it spread to the middle east, Africa and Spain, arriving in Italy about 1200 years ago. The first eggplants grown in England were small and egg shaped which led to the English name eggplant. Aubergine is derived from French.

The plants are small bushes with soft, downy, oval leaves, and often spiny stems. The mauve flowers are quite beautiful. Botanically the fruit is a berry and is typically black, shiny and oval in shape, although they are available in different colours and shapes.

Site and soil

Eggplant can be successfully grown outdoors in Canberra particularly with careful variety selection. Being a fruiting plant, eggplant requires at least 6 hours of full sun per day. Choose a warm, sunny, ideally north facing, site.

Prior to planting add compost and a complete organic fertiliser to the soil. They like a fertile, well-drained soil with pH of between 6.2-6.8.

If growing in pots it is very important to boost the potting mix with complete organic fertiliser.

For details on preparing the soil and pots, including the use of lime, dolomite, gypsum and fertilisers please refer to the COGS guide to garden bed preparation.

Planting Seeds and Seedlings

If starting eggplant from seed this should begin in mid-August. The optimum germination temperature for eggplant is 30⁰C. Therefore, the most successful method is to plant seed into cell trays or trays and provide bottom heat by using a heat mat or hot water bottle wrapped in newspaper or a tea towel. Warm, sunny places inside near a window are also suitable for germination. To maximise germination a soil temperature probe and thermostat are useful to ensure the soil temperature is maintained at between 24-32⁰C. Germination will occur without heat but is likely to be much slower.

As soon as the seeds have geminated, they need full outdoor daylight or the equivalent provided by grow lights. Once the seedlings have developed true leaves, and are around 4-5 weeks old, they will grow better if transplanted into a pot to give the roots more space and allow them grow on before planting outdoors. Advanced plants will fruit earlier. Remember to protect your seedlings from the cold.

Prior to planting, all seedlings should be hardened off. This process takes about one week and involves gradually increasing the length of time that the plants are exposed to full sun. If this is difficult to do prior to planting, an alternative is to make a shade cloth cover over the garden bed containing the eggplants and gradually reduce the amount of cover over a week or two. 

Plant seedlings approximately 30cm apart. After planting, it is a good idea to water them in with a seaweed solution. The soil and plants will benefit from being mulched with organic matter such as spoiled lucerne, pea straw, sugar cane mulch or leaf mould.

Cultivation

Since eggplant is cold sensitive, seedlings, whether purchased or raised yourself, should be planted out after the danger of frost has passed and the soil is warm. In Canberra this is usually sometime in November. If the overnight temperature is forecast to be 2⁰C or less cover plants with frost cloth or an upturned bucket to protect from frost. Covering plants can make a difference of 5⁰C.

If seedlings do not “take off” after a couple of days a foliar (leaf) spray can be very beneficial. This involves spraying the leaves of the plants in the early evening with a solution of seaweed, seaweed and worm juice or other trace element-based product. You should notice an improvement in the plants with 24-48 hours after applying a foliar spray. Feeding plants in this way stimulates plants to produce carbon rich root exudates which feed soil microorganisms who in turn provide mineral nutrients to the plants and can be done monthly during the growing season. 

Weeds can compete with crop plants, therefore weeding at the seedling stage is beneficial. Mulching will supress weeds to some extent.  Weeds will be less problematic once plants form a canopy shading the soil.

Eggplants may be pruned and staked to keep the plants straight.

Plants may need to be fertilised mid-season using a side dressing of complete organic fertiliser.

Water is the number one requirement for plant growth. Newly planted seedlings will generally need to be watered once or twice a day. The easiest way to gauge whether plants need watering is to insert a finger into the soil. If it is wet and soil adheres to the finger it does not need watering. If it feels dry it needs watering. Soil should feel cool and moist. Try and maintain soil in this condition by regular watering.

Harvesting

Harvest fruit when it is shiny and still slightly soft to the touch. Fruit in Canberra will probably not get as large as eggplants you are used to seeing for sale so do not worry if the fruit is small. If you leave fruit until it is hard it is most likely that the seeds have started to develop and the fruit will not be tasty. 

Fruit can be gently removed from the plant using a gentle upward pull or they can be cut off with secateurs or a sharp harvest knife. Mind the spines! As is usual with fruiting plants, harvesting regularly will stimulate more flowers which means more fruit! Eggplant can continue producing well into autumn. 

Problems

There are numerous pests and diseases that can affect eggplants. The best approach is to have a reliable Australian reference book for example, Garden Pests, Disease and Good Bugs by Denis Crawford.

A general strategy to follow with any problem is to observe the plant carefully before taking action. Identify the problem then carefully consider the course of action. For example, with pest insects, you often can see a predator nearby. If you watch and wait the predator may deal with the problem for you. Beneficial predatory insects which feed on pest insects can be purchased from suppliers such as Bugs for Bugs. If the problem needs further action the above recommended book has suggestions. 

Practice lengthy crop rotation to avoid Verticillium wilt and other diseases. A four-to-five-year rotation for all Solanaceae crops is recommended.

Here are a few common issues with eggplant.

• Silvering of leaves after planting out can occur if plants were not hardened off. This is due to the high light intensity destroying the photosynthetic pigments. The plants will recover but it may take a while as the plant will have lost its capacity for photosynthesis
• Tomato russet mite. Affects tomatoes but can also affect eggplant. If the leaves start dying off from below, curl downwards, dry out and turn bronze, and the stems lose their hairs, get out your magnifying glass and see if you can see the tiny mites above the damaged part of the plant. The mites move up the plant creating havoc on their way. Predatory mites are a natural predator. A solution is to spray with wettable sulphur, lime sulphur or tomato dust. The odour from the sulphur kills the mites. It is important to act quickly on this one as plants can die within a week. At the end of the season keep affected plants and mulch out of the compost to break the life cycle.
• Bud worms are caterpillars hatching from eggs laid by a moth. The caterpillars bore holes in flowers and fruit. Larvae leave holes in leaves. They affect a large range of plants. Miniature Trichogramma species wasps parasitise the eggs, larger wasps eat the caterpillars. Try to find the eggs and see if they have been parasitised. Parasitised eggs will be a dark colour. Other natural predators include: parasitic flies, assassin bug, damsel bug, shield bug, lacewings, ladybirds and spiders.  Minor infestations can be dealt with by picking off the caterpillars and squashing them. Infested fruit should be destroyed (e.g. by drowning in a bucket of water) to break the life cycle. Dipel which contains the bacteria, Bacillus thuringiensis, can be used to kill major infestations of caterpillars. 
• Queensland fruit fly has become a problem in Canberra mostly affecting fruit late in the season. Exclusion using fine netting over plants or around individual fruits is successful.

Recommended Varieties

It is worth sourcing varieties that are bred to produce outdoors in a cool climate. Suitable seed is widely available and locally grown seedlings can be purchased either at Farmers Markets or directly from growers. Varieties that have been grown successfully in Canberra include Tonda Bianca, Black beauty, Fantastic, Diamond, Fairy Tales, early long purple, Rosa Bianca and Listada de Gandia.

References

1. Bubel, Nancy. The New Seed-Starters Handbook. Rodale Books, 2018.
2. Crawford D. Garden Pests, Disease and Good Bugs. Australia: ABC Books; 2015.
3. Dove, Helena. Botany of the Kitchen Garden, Kew Publishing, Royal Botanic Gardens Kew, UK, 2023. 
4. Fanton, Michel and Jude. The Seed Savers Handbook. The Seed Savers Network, Australia, 1993.
5. Johnny’s Selected Seeds. Eggplant Growing Information [Internet]. 2023 [cited 2025 Mar 25]. Available from: https://www.johnnyseeds.com/growers-library/vegetables/peppers/peppers-key-growing-information.html