Auberginen aussäen: Diese drei Wochen entscheiden über die Sommerernte

If you want to harvest plump aubergines in summer, check the calendar now – there is only a very narrow window for sowing.

Many home gardeners are puzzled by undersized fruit in August even when their plants appear healthy. The cause often lies months earlier: seeds sown too late leave the crop chasing the season. Getting the timing right, alongside a few straightforward measures, now creates the conditions for baskets full of produce.

Why aubergines do not forgive a late start

Aubergines are true sun-lovers. Originating in warm climates, they are highly sensitive to cooler conditions. Once temperatures fall below roughly 10°C, their growth almost stops altogether. They need reliably warm air at around 20°C to develop strongly, while the soil should be slightly warmer still.

This preference for warmth has clear implications for growing them at home. Late sowing may still produce robust-looking plants, but they will not have enough time to form sufficient flowers and fruit. As daylight hours shorten and nights cool down, fruit either remains small or simply fails to ripen.

“Sowing is not a minor detail with aubergines – it often determines whether you harvest kilos more or less in summer.”

This is even more apparent in areas with shorter summers, such as northern and central Germany or higher-altitude locations. In these places, every week genuinely matters.

The crucial three weeks for sowing aubergines

Without a heated greenhouse, the best time to sow is usually from around mid-February until very early March. These roughly three weeks establish vigorous young plants that can be moved outside in good time and crop heavily by high summer.

Those who wait until April are often in for an unwelcome surprise. The plants may look attractive and produce plenty of foliage, but flowering begins late – sometimes not until the end of August. By the time the first fruits are developing, autumn is already approaching and cold nights slow everything down again.

If you are unsure, it is generally better to begin a few days early rather than late. As long as the seedlings are kept warm and in bright light, they will cope well.

Heat, light and patience: the foundations of successful sowing

Aubergine seeds require genuinely warm conditions to germinate. The compost should be between 22 and 25°C; otherwise, seeds will be slow to emerge or may not germinate at all.

Suitable options include:

• a heated windowsill or heat mat
• a covered mini greenhouse
• a spot above a gently warm radiator, checked with a thermometer

Germination normally takes between 7 and 15 days. If nothing has happened after a week, this does not automatically mean the attempt has failed. Often, the temperature has simply not remained consistently warm enough.

Once seedlings emerge, light becomes the key consideration. Young plants need the brightest possible position or they will become leggy: their stems grow long and thin, and snap easily. Such plants will crop far less well later on.

Sowing aubergines step by step

You only need simple materials for a strong start. Use a loose, fine-textured compost intended specifically for sowing or raising seedlings. It should be clean and as free from germs as possible.

How to sow the seeds

• Fill clean seed trays or small pots with seed compost.
• Place 1 to 2 seeds in each pot.
• Cover the seeds with no more than 1 centimetre of compost.
• Gently firm the surface so that the seeds make good contact with the compost.
• Moisten using a fine spray, preventing the seeds from being washed away.
• Cover the container with a transparent lid or film to retain humidity.

A small seed-selection trick can also help: put a few seeds into a glass of water. Seeds that have sunk after around five minutes usually appear more viable. Many floating seeds are often empty or poorly developed and can be removed.

Do not forget potting on: the important intermediate stage

After around five to six weeks, young plants will usually have several small leaves and their first fine network of roots. At this point at the latest, move them into individual, slightly larger pots. This prevents roots competing with one another and gives each plant room to grow strongly.

When pricking out, handle seedlings by a leaf rather than the stem, and plant each one at exactly the same depth as before. A loose compost with fewer nutrients encourages good branching.

Plants should not be put outside until there is no longer any risk of late frost. In many areas, the period after the mid-May cold spell traditionally known as the “Ice Saints” is used as a guide. A cold snap before then will immediately halt growth and can set the entire crop back.

In a vegetable bed or raised bed, aubergines need adequate spacing. A distance of 25 to 30 centimetres within the row is a useful guide. Air movement helps prevent fungal diseases, and these plants tolerate competition poorly.

Good companions: plants that support aubergines

Suitable companion plants can provide considerable support in the vegetable plot. They occupy different soil layers, attract beneficial insects or help deter pests.

• Basil: works well both in flavour pairings and in the bed, attracts insects and may confuse pests.
• French marigolds (Tagetes): add colour and are considered protective against certain soil parasites.
• Leaf lettuces: make use of ground-level space, provide some shade and help the soil retain moisture.

These mixed plantings improve the microclimate around aubergine plants. They use the available space more effectively, while planted soil stays loose and moist for longer.

Common mistakes that cost you the harvest

The most frequent mistake is starting at the wrong time. Temperature issues follow closely behind: plants kept too cool stagnate, whereas excessively warm, dry central-heating air causes them to wilt.

Watering also requires a careful touch. Aubergines prefer consistently moist conditions, but not waterlogged compost or soil. Long dry periods followed by heavy watering quickly cause stress, flower drop or split fruit.

Another common problem is insufficient light. A dark windowsill is rarely enough. Choose a truly bright location, ideally a south-facing window or, if necessary, a grow light. This is the only way to keep young plants compact and sturdy.

“Anyone who treats aubergines like tomatoes often fails on two points: too little warmth and too much patience with weak young plants.”

Why an early start pays off in summer

Using the three key weeks in late winter results in significantly higher yields by high summer. Plants flower sooner, continue setting fruit for longer and cope better with the first cool nights, because many fruits are already nearly ripe.

With steady warmth, plenty of light and regular but careful watering, these plants become real fruit-producing machines. Harvesting can then continue for several weeks, bringing substantial, glossy aubergines into the kitchen rather than only the occasional small fruit.

Additional practical tips for even better results

Gardeners in cooler areas can lend their plants a helping hand with a few simple measures. Black mulch film or a dark layer of compost warms the soil more quickly. A transparent polythene tunnel protects plants from wind and cool nights in early summer.

Targeted feeding is also worthwhile. Aubergines are among the more nutrient-hungry vegetables. Mature compost, organic tomato fertiliser or well-rotted farmyard manure in the planting hole provides a sustained supply of nutrients. The important point is to give several small applications rather than one large dose, avoiding root scorch.

If plants become very tall and heavily leafy, lightly supporting them with a cane and ties is worthwhile. This prevents heavy shoots carrying ripening fruit from snapping. A few unnecessary side shoots can be carefully removed so that the plant directs its energy into fewer, but larger, fruits.