Chillies

Start from seed: August-September

Optimum soil temperature for germination: 27-35°C

Plant seedlings: November-December

Plant spacing: 30-45 cm

Days to maturity: 60-100 days, some up to 180 days

Introduction

Chillies belong to the Solanaceae family, which also includes tomatoes, eggplants, and capsicums. The feature that distinguishes chillies from capsicums is a compound called capsaicin, which is responsible for the heat in chillies. Most of the capsaicin is contained in the seeds and the white ribs inside the fruit.

There is some controversy about the origin of chillies, but it is generally accepted that the ancestors of chillies originated in Bolivia and then spread through Central and South America. Chillies were recorded as reaching the Philippines with the Portuguese in the 1500s and then spread to China, where it became known as “foreign pepper” and led to the development of spicy regional cuisines like Hunan and Sichuan.

Chilli heat is measured in Scoville heat units, a system of measurement devised in 1912. The scale refers to the number of times dissolved chilli extracts can be diluted with sugar water before the capsaicin can no longer be tasted.

In warmer climates, chillies are grown as perennials; however, in Canberra, unless you have a greenhouse for overwintering, chillies are grown as annuals.

Site and soil

Chillies thrive in well-drained, fertile soils with a pH of approximately 6.5. They require abundant phosphorus and calcium for the best results. Like other fruiting plants, chillies need at least 6 hours of full sun per day, so choose a warm, sunny, ideally north-facing site.

Prior to planting, prepare your garden bed by incorporating compost and a complete organic fertiliser into the soil. If growing in pots, it’s essential to enrich the potting mix with complete organic fertiliser.

For details on preparing 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

Chilli seeds should be sown in August or about 8 weeks prior to transplanting outdoors. The optimum soil temperature for germination is between 27-35°C. Chilli seeds germinate very slowly in cooler soil, so providing bottom heat using a heat mat, hot water bottle wrapped in newspaper, or a warm sunny indoor spot is beneficial for successful germination.

Sow seeds in cell trays, or shallow trays, approximately 6mm deep. When the first true leaves appear, transplant seedlings into 5cm cell-type containers or 10cm pots. Grow plants at approximately 21°C during the day and 16°C at night.

Cold Treatment Exposing seedlings to controlled cold treatments can increase flower and fruit production. This is called vernalisation. When the third true leaf appears, grow the plants at a minimum night temperature of 12-13°C for 4 weeks. The plants should receive full sunlight during this period. After 4 weeks, adjust temperature to 21°C day and night. If using this technique, chillies should be seeded 1-2 weeks earlier than usual.

Prior to planting outdoors, 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 and gradually reduce the amount of cover over a week or two.

Cultivation

Transplant chilli seedlings outdoors after all danger of frost has passed and when the soil is warm and weather has settled. In Canberra, this is usually sometime in November. Ideal seedlings have buds but no open flowers.

Plants seedlings approximately 30-45cm apart. Water-in transplants using a seaweed solution. Mulch with organic matter such as spoiled lucerne, pea straw, sugar cane mulch, or leaf mould to conserve moisture and suppress weeds.

Seedlings can be protected by using caterpillar tunnels constructed with polypipe or wire hoops covered in horticultural plastic or frost cloth. The advantage of horticultural plastic is that is it UV stable and transmits light. These tunnels can also be used to extend the season into late Autumn. Remove covers in sunny weather above 29°C to prevent blossom drop and heat damage and don’t forget to water.

If seedlings don’t establish well after planting, apply a foliar (leaf) spray in the early evening with a solution of seaweed, seaweed and worm juice, or a trace element-based product. This stimulates plants to produce carbon-rich root exudates, feeding soil microorganisms that provide mineral nutrients to the plants. Foliar sprays can be used monthly to increase plant resilience.

Weeds can compete with crop plants, so weeding at the seedling stage is beneficial. Weeds become less problematic once plants form a canopy shading the soil.

Plants may need to be fertilised mid-season using a side dressing of complete organic fertiliser. Water regularly, maintaining cool and moist soil conditions.

Harvesting

Pick the first chillies promptly when they reach full size to encourage further fruit set. Generally speaking, the larger the fruit, the less intense the heat and the sweeter the flesh.

Harvest chillies by cutting them from the plant with secateurs or a sharp knife. Handling hot chillies can cause skin irritation, so wearing gloves is recommended when harvesting very hot varieties.

Problems

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

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.

Practicing good garden hygiene, crop rotation, and maintaining plant vigour by providing adequate nutrients are key strategies for prevention.

Here are some common issues with chillies:

Blossom-end rot which also affects tomatoes. The symptom is brown, sunken, watery areas at the bottom (blossom) end of the fruit. The cause is an inadequate supply of calcium resulting in plant tissue break down. Inadequate watering, waterlogging, over use of fertilisers or low soil pH can all reduce the availability of Calcium leading to this condition. Prevention involves maintaining a soil pH of around 6.5, deep and regular watering, using organic fertilisers, ensuring your soil is not Calcium deficient, mulching plants and avoiding severe pruning. Some varieties seem more prone than others to Blossom-end rot.
Sunscald is the equivalent of sunburn. Fruit develops papery blisters which can lead to secondary infection and pest infestation. It can be avoided by selecting varieties with good leaf cover or by shading plants in periods of intense bright light.
Tomato russet mite. Affects tomatoes but can also affect chillies. 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.
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.

Insect pests. Control climbing cutworms with Bacillus thuringiensis (Dipel) or with paper cylinder collars.
Poor fruit set. Big bushy plants with few chillies can be caused by excess nitrogen, hot or cold temperature extremes during flowering, injury from pests, or poorly-adapted varieties.

Recommended Varieties

There are five species of capsicums and chillies and over 4000 varieties.

Capsicum annuum: Most common species, include bell and sweet peppers, many mild to medium-hot varieties suitable for Canberra.

Capsicum frutescens: most common chilli. Includes Tabasco, African bird’s eye, and Thai hot chillies.

Capsicum chinense: Includes habanero, Scotch bonnet chillies, and Carolina Reapers, which are very hot but can be challenging to grow in Canberra’s climate without greenhouse protection.

Capsicum pubescens: black wrinkled seeds, purple flowers and leaves covered in a fuzz.

Capsicum baccatum: large flowers and leaves and extremely hot fruit.

Varieties that have been grown successfully in Canberra include Jalapeño, Cayenne, Thai Hot, Hungarian Hot Wax, and Bishop’s Crown.

References

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