Jalapeños are a good chilli to grow at home because their fruits are useful in everyday cooking and they don't require the enormous space of a vegetable vine. You can pick them green for a fresh, fairly crisp chilli or leave them to ripen red for a different flavour. In Britain, the challenge is giving them enough warm growing weather to flower and develop a worthwhile crop.
A greenhouse or sunny conservatory offers the most reliable conditions, although a warm sheltered patio can work in a good summer. Start early enough, choose a healthy plant and keep the roots consistently moist.
Choose a variety suitable for a pot
Jalapeños belong to the species Capsicum annuum. Different cultivars vary in plant size, fruit shape, productivity and heat. A compact variety can be useful for a windowsill or patio, while larger plants need more root space and support.
Buy seeds from a reputable supplier and read the packet carefully. If the fruit size and heat level matter to your cooking, look for a named variety rather than an unidentified packet marked simply 'hot pepper'.
The Royal Horticultural Society describes the typical heat of jalapeño chillies as moderate compared with very hot types, although actual heat varies with the plant and growing conditions.
When to sow jalapeño seeds
Chillies benefit from an early indoor start because Britain's summer is relatively short. Sow from late winter into spring where you can provide warmth for germination and strong light after seedlings emerge.
Use clean modules or small pots of peat-free seed compost. Sow at the packet's recommended depth and keep the compost gently moist. The RHS suggests approximately 21°C for chilli seed germination.
Once seedlings appear, remove any propagator cover and give them bright light. An overheated, gloomy windowsill encourages weak stretched stems. If the seedlings become crowded, move the healthiest plants into separate small pots.
Potting on young chilli plants
When roots have filled the first container, transfer each seedling into a slightly larger pot of peat-free multipurpose compost. Handle the rootball gently and water to settle it.
Don't move a tiny plant directly into a huge pot that remains wet for days. Increase the pot size in stages as roots develop. A sturdy plant with healthy leaves will respond better to its final container than one that has become pale and leggy.
Wait until frost risk has passed before moving chillies outdoors. Even frost-free but cold nights can slow them sharply, so harden them off gradually and choose a particularly sheltered position.
How big should the final pot be?
The RHS recommends a pot of about 22cm for one ordinary chilli plant, although vigorous cultivars may appreciate more room. Use a container with drainage holes and fresh compost. Don't squeeze several mature plants into one small pot.
Place it in the warmest, sunniest suitable part of your growing area. Outdoors, a south-facing patio close to a wall can provide shelter. In a greenhouse, leave enough room around the foliage for ventilation and easy inspection.
A taller plant may need a cane. Put it in early to avoid damaging established roots later, and tie stems loosely to support them as fruits grow heavier.
Watering jalapeños
Chilli plants prefer an even supply of water during active growth and fruiting. Check compost moisture below the surface and water thoroughly when needed. A small pot in strong summer sunshine can dry surprisingly quickly.
Allow the surplus water to drain rather than leaving roots standing in a saucer full of water. Repeated drought can make flowers drop and interrupt fruit development, while saturated compost can damage roots.
If leaves wilt, check the pot before adding water. Hot weather can cause temporary drooping, but the same symptom can appear when roots are struggling in overly wet compost.
Feeding for flowers and fruit
Once the first flowers appear, a high-potassium liquid feed suitable for tomatoes or chillies can support fruit development. The RHS recommends regular feeding of container chillies during flowering, following the product's instructions.
Avoid applying extra fertiliser in the hope of forcing quick results. Excess feed can harm roots or produce unbalanced growth. Warmth, sunlight and steady watering have to be in place first.
Some growers pinch out the leading growing tip to encourage branching, but this can delay cropping. On a short UK growing season, a naturally well-branched plant often needs no complicated pruning.
Will jalapeño plants pollinate themselves?
Jalapeño flowers are generally self-fertile. Gentle air movement and visiting insects can help pollen transfer. In a greenhouse, appropriate ventilation is useful for temperature control as well as flower development.
When conditions become extremely hot, cold or dry, flowers may fall before fruit forms. This doesn't necessarily mean you need more feed. Review the environment and avoid overheating a closed greenhouse on sunny days.
A healthy plant should gradually develop small green chillies where successfully pollinated flowers were growing. Allow fruit to swell without repeatedly handling it.
When are jalapeños ready to harvest?
Jalapeños are commonly picked green when fruits have reached a useful size and feel firm. If left longer they can turn red, developing a different flavour and often greater sweetness.
Use clean snips to cut the stalk rather than tugging at a fruit, which can tear a branch. Regular picking encourages the plant to continue developing younger fruits while growing conditions remain favourable.
Some jalapeños develop pale cork-like lines on their skin. This is called corking and can be normal for the variety; on its own, it is not a sign of disease. Judge whether the fruit is otherwise sound.
Wear gloves if handling large quantities, avoid touching your eyes and wash hands thoroughly after preparation. Jalapeño oils can irritate sensitive skin.
Can jalapeño plants survive winter?
Chillies are tender perennials in suitable climates. Some plants can be kept over winter indoors in a bright, frost-free position, cut back appropriately and watered sparingly until growth resumes.
In Britain, the difficulty is providing enough winter light and suitable temperatures while avoiding overwatering. Not every plant will survive, and starting fresh seeds each year may be easier.
If you want to try, inspect the plant for pests before bringing it inside. Aphids and other sap-feeding insects can spread to houseplants.
Common jalapeño growing problems
Flowers fall without fruit: Heat, cold, drought and poor conditions may interfere with fruit set.
Leaves turn yellow: Check water supply, drainage, light and possible pests before adding fertiliser.
Fruits stay small: Variety, limited roots or a short cool summer may restrict development.
Plants grow very slowly: Low temperatures are a common reason, especially after premature outdoor planting.
Tiny insects on soft shoots: Inspect for aphids and use appropriate edible-crop pest guidance.
Starting with two chilli plants
Raise two or three seedlings in spring, pot them on as roots develop, then give each a sunny, warm final position. Water consistently, feed during flowering and pick fruits as they reach the size you want.
You don't need an elaborate chilli-growing setup. A suitable variety and enough warm sunshine usually make the biggest difference.
Source
Royal Horticultural Society: How to Grow Chilli Peppers.