Solanum melongena
Vegetables in the Solanum or nightshade family are mostly fast growers, and plants are killed by frost. In the same family as aubergines are tomatoes, potatoes, sweet peppers, chillies, tobacco, and ornamental plants called nicotiana.
In tropical regions where they originate, such as Africa and India, aubergine plants are perennials. In temperate climates or subtropical climates with cooler winters, you can grow them as perennials if you can manage to keep them alive through winter. Whether this is worthwhile is another matter. Mostly they are grown as annuals.
Harvest period
- Days from seed to first harvest: 130 under cover/160 outside in a temperate climate.
- Days from seed to first harvest: 100 under cover/130 outside in a warm climate.
- Best climate is one with hot summer days – 24° C/75° F and higher, with sufficient moisture for the roots to sustain rapid growth.
Why grow them
There is something fascinating and beautiful about aubergines, and it’s a lovely experience to see them growing and then fruiting. Sadly, once they are cooked, the difference in flavour between homegrown and store-bought is not huge. Aubergines are valued partly for their ability to soak up juices and oil, rather like potatoes.
It is exciting to try different varieties though, as there is a huge range of shapes and colours to experiment with that you won’t find in the shops.
Suitable for containers/shade?
- Yes, preferably with a smaller plant variety such as Pot Black, whose fruits are large enough to grow a few meals.
- Best not to grow them in shade, unless your summers are really hot – see below for more detail.
Conditions for success
Aubergine plants need warmth at all stages of growth, and I categorise them with melons for their relative growing difficulty in regions with cool summers. Ideal summer temperatures are in the range of 12–20 °C/54–68° F by night, and 24–35 °C/75–95 °F by day.
- Temperature is the key. Homeacres, for example, is a little too cool, with an average temperature from June to August of 11 °C/52° F by night and 21 °C/70° F by day. These figures are marginal for outdoor aubergines, so they are more worthwhile under cover.
- To enjoy harvests in summer, rather than autumn, you need to have warmth for propagation in order to sow early and keep plants growing. In cool climates, it may be as long as two, or even three months before it’s warm enough to transplant.
- The soil needs no special preparation, just the same compost mulch or cover as you apply for tomatoes and cucumbers. We usually spread this once a year, in May or late spring under cover, after clearing winter vegetables and before the summer planting
Varieties
There are many varieties available, but some are poorly maintained. Ones that used to be reliable every summer, I now find less so. It’s why I sometimes recommend F1 hybrids, although you may be fortunate and find a good open-pollinated variety.
If so, and if your summer season is long enough for the fruits to go to seed, with the flesh inedible by that stage, it’s worth saving seeds. Aubergine flowers self-pollinate, which means you can save seed from just one variety, and the flowers will not have cross-pollinated with any neighbouring and different variety.
Black Pearl F1 is my favourite for heavy cropping and a long season of harvest, with large black fruit. For growing in containers, I am impressed by Pot Black F1. My other favourites are many of the traditional Thai varieties such as Thai Long Green.
Two varieties I am unimpressed by are Pianta Delle Uova and Melanzana Prosperosa, both from Franchi seeds. The Pianta Delle Uova grew a large plant but with almost zero food to eat, just a smattering of little white fruits. The Melanzana Prosperosa gave one or two very pretty fruits per plant over a long period of growth. They were tasty but so few, and represented a waste of time and effort.
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In cooler climates, such as here in the UK where every growing day makes a difference, it’s worth sowing early enough that you can then pot on small plants to keep growing. We need large plants at the transplanting stage.
Firstly, prick out seedlings from the seed tray into a module tray, when about two weeks old and with just two leaves. After another four weeks, pop the module seedlings into a pot around 7 cm/3 in diameter. After two more weeks, if not ready to transplant, pot on again into a 10 cm/4 in pot for 10–14 days.
Sowing conditions
Warm: 21–30 °C/70–86 °F.
Sowing time
From late winter to early spring.
Sowing method
In a seed tray to prick out into small modules.
Pot on?
When plants are six to eight weeks old. Pot on again after another two weeks if needed, as in the photos below.
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Avoid overcrowding – these plants need to grow and crop for a few months, which means there needs to be empty space around the base. Soon after transplanting the soil will be full of their roots.
I would not try to grow other vegetables as an intercrop, but you could plant basil to crop for a while between aubergine plants.
Low-growing flowers, such as dwarf marigolds, flower well under aubergine plants and look really good, probably because their roots collaborate nicely with the aubergine roots. Self-seeding may be an issue, but it’s not a problem if there is enough frost in winter to kill the thousands of seedlings.
Transplant size
15–25 cm/6–10 in high; plants may or may not be flowering.
Transplant time of year
After the last frost date – usually in late spring under cover, or early summer outside.
Spacing
45–60 cm/18–24 in allows for large leaves on vigorous plants, and fruiting for ten weeks or more.
Support
Either grow as unpruned bushes with a stake in the middle, or as cordons up one or two strings per plant. If the latter, place the string end under the rootball when planting – see photo above and further details below.
Outdoor aubergines, on a compost heap of warm horse manure
Filmed in 2018, an unusually warm summer here. Good weather combined with warmth for the roots resulted in fine growth and harvests.
This bed of warm manure is a spin-off from the hotbed we make for greenhouse propagation. Then the ingredients have value as compost for the garden in late autumn. It might not be worth trying to make one specifically for aubergines! See what you think.
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How often
Daily for the first week after transplanting, then every two to three days, with an increasing amount as plants grow.
How much
In hot weather, aubergine plants are thirsty: they have big fleshy leaves and grow extremely fast. Plus they can fruit heavily when everything goes well. If you under-water, you will notice leaves wilting on a hot afternoon, and the fruits will be harder and less shiny.
Extra mulch to retain moisture?
For a variation that you could use in hotter climates, see the photo from Thailand below. Mulches of un-decomposed materials are often light in colour, keeping the soil cooler and moister.
An important point about mulches of straw and grass is that although they conserve existing moisture in the soil, they can also slow down the penetration of summer rainfall, especially when the rainfall is only a small amount.
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A key requirement for successful growing in pots and containers, even more than in beds, is to use a well-structured compost with a long-term supply of nutrients. I have trialled many composts and find best long-term growth from organic-approved ones.
In genuinely organic composts, the nutrients come from decomposed plant matter and not from added chemical feeds.
- Unlike for food and beverages, the label ‘organic’ on sacks of compost and manure means nothing unless verified by a certifying symbol from a national body, such as The Soil Association (UK).
- Nutrients from chemical feeds (‘synthetic’, ‘non-organic’) are mostly soluble in water and need careful management.
- Nutrients in organic and homemade composts do not wash out, and release slowly over a long period.
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For bush plants, your work depends on the variety. Some are vigorous and need tying to or around the stake you have put in. Also, it’s worth removing old leaves and any rotting fruit.
For cordon plants with two leading stems, with your two strings already set under the rootball, watch for the first strong side shoot. Allow this to grow into a second upward stem. Then, about three weeks after you first let it grow into a stem, twist it gently around the second string.
Cordon aubergines need less twisting around strings than tomatoes because their stems develop more slowly. Removing side shoots is similar to tomatoes and needs to be done regularly, but there are less of them so it’s not too onerous, as you see in the video.
- Plants self-thin their fruits! When a lot have been pollinated, you will see a few decay and then drop off. This is nothing to worry about. You can thin more small fruits if you want larger aubergines.
- Unless your garden is barren of insects (unlikely), pollination will look after itself. If fruit are not setting, it’s more likely to do with a shortage of moisture, issues of warmth, or perhaps the variety.
It’s not usually necessary to thin fruit, just remove any rotting ones.
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Assessing when aubergine fruits are ready to harvest is not always straightforward. It’s not a question of size or fatness, because many varieties crop small and thin fruits. What you are looking for is a relative degree of plumpness and firmness, and the skin still being glossy, rather than the matt appearance of older fruits.
If you leave aubergines longer than necessary before harvesting, you lose food. They switch from growing flesh to developing seeds. Best harvests occur when you keep picking regularly, and before you see any signs of them going seedy.
- Picking is regular and frequent through summer’s second half, and finishes in early autumn.
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Which pests are likely, and when
- For pest protection, there are no specific measures needed.
- The possibility of red spider mite is a worry.
- Aphids should not cause much of a problem.
Red spider mite (Tetranychus urtica) is more difficult to deal with because it’s unpredictable and almost invisible to the naked eye. You don’t see its first incidence, from early to midsummer. Then suddenly there are many leaves turning pale green and then yellow, with faint cobwebs on their undersides. By this point, it is too late to rectify matters.
Aphids such as whitefly (Trialeurodes vaporariorum) and greenfly (Macrosiphum rosae) like aubergines, but watering well in spring enables healthy growth to continue until the joyful time of late spring. Aphid populations then reduce as predators start to arrive, especially by early summer.
Aim to prevent red spider mite, rather than having to deal with it. You need a combination of healthy soil, good watering, suitable varieties, and possibly to buy a predator, the Phytoseiulus persimilis. However, they are not cheap and are only worthwhile if you are growing quite a few plants.
Strong, healthy plants are less likely to suffer from red spider mite. In the 2020 greenhouse I lost two plants of Thai Long Green to red spider mite – so badly damaged that I removed them in late summer – while the neighbouring Black Pearl continued to grow without any red spider mite. Perhaps the Thai plant was weaker, from the lack of warmth it is accustomed to!
Disease
- Bacterial soft rot (Erwinia carotovora).
This can appear quickly, and apparently randomly. Affected plants suddenly have limp leaves, which turn almost completely brown, or brown in large patches.
A few plants suffer this occasionally and, it seems, randomly. I remove them to the compost heap. I have had aubergines suffer and die within two weeks, without the disease spreading to neighbouring plants.
Other likely difficulties are few
- Poor harvests occur where warmth is limited.
- Lower leaves often turn yellow quite quickly and have spots, both of which are normal in my experience. Even some limpness of isolated leaves may happen, without it being a terminal illness.
- Aubergines do not suffer late blight, even though related to tomatoes.
- In warm climates (not the UK), they suffer flea beetles – water can help.
And finally
Clear
Because aubergine plants need warmth to perform, their useful life finishes before mid-autumn.
Clear plants when you see no more baby fruits, and/or they have few healthy leaves.
Follow with
- Follow under cover with transplants of salad leaves through winter – see photo above.
- Follow outside, in early to mid-autumn, with transplants of salad onions and cabbages for spring – in containers as well as beds.
- Follow with winter salads in containers – they need little feed, you can just spread 5 cm/2 in of multipurpose compost on top before planting.
