Capsicum

Start from seed: August-September

Optimum soil temperature for germination: 27-32⁰C

Plant seedlings: November-December

Plant spacing: 30cm

Days to maturity: 50-100

Introduction 

Capsicums, also known as peppers, belong to the Solanaceae family, which also includes tomatoes, capsicum and chillies.

Capsicums are thought to have originated in Bolivia then spread throughout Central and South America where they have been cultivated since at least 7000 BCE. They reached south east Asia and India by the 1500’s then arrived in China. It is thought Columbus introduced capsicums to Europe in the 1600’s. 

Capsicum comes from the Greek Kapto meaning “to bite”. However, sweet peppers contain a recessive gene which means they do not produce capsaicin which is responsible for the heat in chillies. It is a perennial plant, that is mostly grown as an annual, bearing small white, cream or purple flowers. The fruit is a green, fleshy berry that ripens to red, yellow or orange. 

Site and soil

Capsicum can be successfully grown outdoors in Canberra particularly with careful variety selection. Being a fruiting plant, capsicum requires at least 6 hours of full sun per day. Choose a warm, sunny, ideally north facing, site.

Prior to planting add compost and a complete organic fertiliser to the soil. They like a fertile, well-drained soil with pH of 6.5.

If growing in pots it is very important to boost the potting mix with complete organic fertiliser.

For details on preparing the soil and pots, including the use of lime, dolomite, gypsum and fertilisers please refer to the COGS guide to garden bed preparation.

Planting 

If starting capsicum from seed this should begin in mid-August. The optimum germination temperature for capsicum is 30⁰C. Therefore, the most successful method is to plant seed into cell trays or trays and provide bottom heat by using a heat mat or hot water bottle wrapped in newspaper or a tea towel. Warm, sunny places inside near a window are also suitable for germination. To maximise germination a soil temperature probe and thermostat are useful to ensure the soil temperature is maintained at between 24-32⁰C. Germination will occur without heat but is likely to be much slower.

As soon as the seeds have geminated, they need full outdoor daylight or the equivalent provided by grow lights. Once the seedlings have developed true leaves, and are around 4-5 weeks old, they will grow better if transplanted into a pot to give the roots more space and allow them grow on before planting outdoors. Advanced plants will fruit earlier. Remember to protect your seedlings from the cold.

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

Plant seedlings approximately 30cm apart. After planting, it is a good idea to water them in with a seaweed solution. The soil and plants will benefit from being mulched with organic matter such as spoiled lucerne, pea straw, sugar cane mulch or leaf mould.

Cultivation

Since capsicum is cold sensitive, seedlings, whether purchased or raised yourself, should be planted out after the danger of frost has passed and the soil is warm. In Canberra this is usually sometime in November. If the overnight temperature is forecast to be 2⁰C or less cover plants with frost cloth or an upturned bucket to protect from frost. Covering plants can make a difference of 5⁰C. The ideal temperature for fruit set is between 18-29⁰C. Very little fruit set occurs below 16⁰C and above 32⁰C. Covers can be used to increase yield and extend the season into late Autumn.

If seedlings do not “take off” after a couple of days a foliar (leaf) spray can be very beneficial. This involves spraying the leaves of the plants in the early evening with a solution of seaweed, seaweed and worm juice or other trace element-based product. You should notice an improvement in the plants with 24-48 hours after applying a foliar spray. Feeding plants in this way stimulates plants to produce carbon rich root exudates which feed soil microorganisms who in turn provide mineral nutrients to the plants and can be done monthly during the growing season.

Weeds can compete with crop plants, therefore weeding at the seedling stage is beneficial. Mulching will supress weeds to some extent.  Weeds will be less problematic once plants form a canopy shading the soil.

Capsicums can be grown using a trellis, such as basket weave trellis, to support the fruit. Staking is effective support to keep the plants upright and fruit off the ground.

Plants may need to be fertilised mid-season using a side dressing of complete organic fertiliser.

Water is the number one requirement for plant growth. Newly planted seedlings will generally need to be watered once or twice a day. The easiest way to gauge whether plants need watering is to insert a finger into the soil. If it is wet and soil adheres to the finger it does not need watering. If it feels dry it needs watering. Soil should feel cool and moist. Try and maintain soil in this condition by regular watering.

Harvesting

Harvest fruit when it reaches the desired colour. Fruit in Canberra will probably not get as large as capsicums you are used to seeing for sale so do not worry if the fruit is small. Late in the season they may not ripen to red, orange or yellow.

Fruit can be gently removed from the plant using a gentle upward pull or they can be cut off with secateurs or a sharp harvest knife. As is usual with fruiting plants, harvesting regularly will stimulate more flowers which means more fruit! Capsicums can continue producing well into autumn. 

Problems

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

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, lengthy crop rotation, and maintaining plant vigour by providing adequate nutrients are key strategies for prevention. A four-to-five-year rotation for all Solanaceae crops is recommended.

Here are a few common issues with capsicum.

• 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 capsicums. 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.

Recommended Varieties

It is worth sourcing varieties that are bred to produce outdoors in a cool climate. The smaller bullhorn and lunchbox type capsicums do well in Canberra. Suitable seed is available and locally grown seedlings can be purchased either at Farmers Markets or directly from growers. Varieties that have been grown successfully in Canberra include Orange Tarta, Red Tatin, Balcanica, Stocky Red Roaster, Lipstick, Sweet Bullnose, King of the North and Lively Orange.

References

1. Bubel, Nancy. The New Seed-Starters Handbook. Rodale Books, 2018.
2. Crawford D. Garden Pests, Disease and Good Bugs. Australia: ABC Books; 2015.
3. Dove, Helena. Botany of the Kitchen Garden, Kew Publishing, Royal Botanic Gardens Kew, UK, 2023. 
4. Fanton, Michel and Jude. The Seed Savers Handbook. The Seed Savers Network, Australia, 1993.
5. 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