How to Grow Aubergines in Cooler Climates

27 January 2012, written by Benedict Vanheems

Delicious as aubergines are (eggplants to those outside Europe), any of us growing in temperate climates will undoubtedly find them just a bit of a struggle. Aubergines hail from India, where temperatures can occasionally top 50°C or 122°F (yes, really!). So with cool, northern summers it should come as no surprise that these plants need as long a growing season as we can possibly muster; it’s very much a case of early to rise and late to bed for these tropical beauties!

Gardeners in temperate climates who try growing aubergines are all-too-often faced with disappointment. Plants put on lacklustre growth, possibly flower and may – just – produce one or two puny, chicken egg-sized fruits. (Perhaps that’s why they’re called eggplants?) I lay part of the blame at the feet of the seed companies, who make outrageous claims that many of the varieties they sell will give a good crop outdoors if grown ‘in a sunny and sheltered position’. That may be the case in a heat wave year, but for a typical summer in the UK I’m afraid this advice simply doesn’t cut it. The only solution for those contending with leaden skies and drizzle comes in the form of a greenhouse where temperatures will sit a few degrees above those outside – enough to make all the difference.

Of course, I cannot speak for those blessed with a warmer climate. There the consistently higher temperatures will more than make up for the longer hours of summer daylight experienced by those of us at higher latitudes. Most American gardeners should be fine growing their eggplants outside following an early start under cover, while those in the Southern states will be able to sow directly outdoors. What follows is advice for those gardening in weaker sunshine levels and unpredictable summers.

Sow Aubergines Early

Don’t wait until spring to make your sowings, start your aubergines off in late winter. You will need to coddle the seedlings but I promise it will be worth it. To minimise root disturbance and make life easier I sow the seeds into modules of seed compost, though you could of course sow into pots of compost and prick out the seedlings into their own pots once they are big enough. Being in the tomato family the seeds look much the same, so they are easy to handle and sow individually. Cover them with a layer of vermiculite or compost and pop them into a heated propagator. Ideally you will want a temperature of 24°C (75°F) for speedy germination, although 21°C (70°F) would be adequate. Keep the compost moist but certainly not wet.

Seedlings should make an appearance within 10 days to two weeks, at which point they can be left to grow on before potting on into 7cm (3in) pots of multipurpose compost/potting soil. Keep them on the warm side with plenty of natural light and pot on again into 12cm (5in) containers as soon as the roots can be seen at the drainage holes. The plants can go into their final positions once they fill these pots, though you will need to make sure you can sustain a cosy environment.

Hot Topic

The question now is how to boost the ambient temperature to coax your plants into flower and, ultimately, fruit. You have two options here: the warmth of a greenhouse or, for the more adventurous or those that don’t have a greenhouse, an enclosed hotbed. Most gardeners may not have heard of a hotbed, let alone used one. A hotbed has nothing to do with heated blankets or sun/tanning beds, but rather the joy of muck or, to be more precise, decomposing muck! As manure breaks down it gives off impressive heat, raising the surrounding temperature on a cold day by as much as 10°C (about 18°F). Hotbeds take advantage of this natural decomposition process by using the heat given off to cajole tender plants into productivity.

Constructing a hotbed is straightforward enough, even if it does require an initial input of muscle. First, dig out a bed to a spade’s depth, fill it with manure (horse is best), then turn it after four days to ensure an even mix of the bacteria and fungi responsible for decomposing. Once it’s kicking off heat decomposition has begun and the muck should be topped off with a 10-15cm (4-6in) layer of soil. Leave for a further few days for the mounded bed to settle then plant your aubergine plants into the soil layer.

To prevent all that hard-won heat from escaping, enclose your hotbed within a cold frame or similar structure, such as a tomato house. You can either dig out the hotbed in an existing frame or lift the structure into place afterwards. Needless to say it makes sense to dig the hotbed to the same dimensions as your covering structure. Aubergines will grow upwards of 90cm (3ft) in good conditions, so make sure the frame or tomato house you use is tall enough for the job. Frames that aren’t tall enough will still give plants a really strong start, even if you have to lift the lids off once the foliage is touching. Fleece can be draped over these plants at night to keep off the chill then removed during the day to allow pollinating insects access.

Greenhouse aubergines should be grown one plant to a pot of at least 30cm (1ft) diameter. Open vents so that bees and other pollinators can find their way in.

Final Steps to Success

To keep aubergines stocky and sturdy remove the main growing point of your plants once they’ve reached 30cm (1ft) tall. This will encourage further branches to develop lower down, thereby ensuring a bushier and shorter plant. Branches may need supporting with canes, particularly when they begin to set their (hopefully) weighty fruits.

Even when growing with lots of compost or manure, both hotbed and greenhouse aubergines will benefit from a weekly liquid feed high in potash to encourage flowers and fruits; tomato feed is fine for this. In cloudy or cool weather gently tap the flowers to encourage pollen to dislodge and fertilise the flowers. Mature fruits can be cut away with a sharp knife; cut them while they are still shiny as dull fruits will be past their best.

Finally, if you are looking for a strong performing variety to give you a head start then I recommend the fulsome ‘Black Enorma’, whose heavy fruits should reward you with plenty of classic black fruits.

By Benedict Vanheems.