Robert Smith

28 Feb 2024 15:02

Sweet Peppers

When it comes to a veggie that really is better when Home-Grown, Sweet Peppers should be high on your list! If you are growing from seed, you not only have a wide array of colours to choose from, including the usual red, yellow and orange; but you can also grow purple, black, and even brown fruits.  No matter if you want large plants for growing in a greenhouse border, or a couple of plants for hanging baskets, there are varieties to suit all spaces and all tastes.



Getting Started

Sweet peppers thrive in the warmth and protection of a greenhouse. It’s best to start by sowing seeds in a heated propagator as soon as you can, with a temperature around 18-21°C (64-70°F) to ensure optimal germination. By starting your seeds in March, you prevent the issue of seeds stretching for the light as they can in earlier months, otherwise you would need to use a grow light to keep them nice and compact.  Sow seeds in individual pots or cell trays filled with peat-free compost, I always like to sow a couple more seeds than what I need.  By doing this you are ensuring you will have plants even if a seed doesn’t germinate, or in case you drop or damage a plant while moving and re-potting them.


Sowing Guidance

Plant two seeds per cell or pot, thinning out the weakest seedling to allow the stronger one to grow.  If you want, you can transplant the seedling you removed, just be careful to lift it by the leaves and don’t crush the delicate stem or it will die.  Keep the compost moist but not waterlogged and provide plenty of light to prevent seedlings from becoming leggy.  If you notice the surface of your compost going a little green, it means that you are watering a little too much and its too wet.  Reduce your watering and remove the surface of the compost, replacing it with fresh to allow you to check on moisture levels going forwards.

Growing On  

Once seedlings have developed their first true leaves, it's time to transplant them into larger pots. Initially, move them into 7.5-10cm (3-4") pots. As they grow, they'll need one final move into 30cm (12") pots or directly into the greenhouse soil or larger containers for varieties like 'Nardello' which can become quite large, however there is a simple trick to get more peppers from your plants, nip themBy nipping the tip (removing the growing point) when the plant is around 15cm tall, you cause it to produce more side-shoots and bush out more, ultimately resulting in a bushier plant with more flowers, and more fruit! 


Did you know that sweet peppers are actually fruits, not vegetables? Botanically, they're classified as berries since they contain seeds and come from the flowering part of plants. 

Whats in a name?  

For those with limited space, 'Redskin' is a compact variety perfect for smaller potsIt produces lots of smaller, red fruit which have a great flavour and can be grown with ease in a 20-25cm pot on a shelf in your greenhouse, perfect for when you don’t have much space, but love peppersIf you're after a cascade of yellow, orange, and red peppers, 'Peppers from Heaven' are an excellent choice for hanging baskets, adding not only flavour but also a decorative touch to your greenhouse. They work well grown in a hanging basket in the greenhouse, taking up no space at all, yet allowing you to grow 3 plants in a 30cm basket with ease; perfect when space is at a premiumFor larger containers or direct soil planting, 'Nardello' offers a traditional, sweet flavour ideal for a range of culinary usesThe long, slender shape could be confused with a chilli pepper, yet it has a deliciously sweet flavour and is amazing when grilled or added to salads or as a pizza topping. 


Care and Maintenance  

Peppers require consistent watering, especially as fruits begin to form. However, avoid waterlogging the soil as these heat loving veggies really don’t like wet roots. Regular feeding with a high-potash fertiliser will encourage growth and more fruit to be produced, you can use regular organic tomato feed or opt to make your own if you have comfrey growing in the garden. Support larger plants with stakes or cages to manage their weight as they grow and produce fruit and keep an eye out for small holes appearing in your peppers, this can be down to ear-wigs or slugs, so be prepared to deal with them as you see fit. 


Did you know Sweet peppers come in a variety of colours, including green, yellow, orange, red, and even purple, each with its own unique taste and nutritional profile. The colour of the pepper can change as it matures, with many starting green and transitioning to another colour as they ripenThere are even varieties which start off black like ‘Sweet Mamba’, changing to red as they ripen. 

How to get the best fruit 

In a greenhouse, manual pollination might be necessary to ensure a good crop. Gently shaking the plants or using a small paintbrush to transfer pollen can mimic the action of bees and aid in fruit set, however I find it easier to leave the greenhouse doors and windows open during the day in the summer, allowing bees access to help pollinateIf the weather if forecast to be windy or cooler at night, close the doors to keep your plants warm and happy. 


How to harvest  

Harvest your peppers when they reach the desired size and colour, but before they start to soften. Peppers are edible at any colour, however they can taste a little more bitter when young and green and remember that purple/black peppers will taste the same as green, so allow them to ripen and change colour if you want sweeter tasting peppersCutting the fruit from the plant with a sharp knife or scissors reduces damage to the plant and encourages further fruiting, so never pull them from the plant as you will damage it. 


Did you know Capsaicin, the compound that gives hot peppers their heat, is absent in sweet peppers, making them perfect for those who prefer flavour without the fire. 


Pests and Diseases  

Keep an eye out for common greenhouse pests such as aphids and spider mites. A healthy, well-ventilated environment and regular inspections can prevent most issues. Should pests appear, natural predators like ladybirds or organic sprays can offer effective control, as can wiping them away with a damp cloth which has been soaked in a water/horticultural soap solution. 



Growing sweet peppers in a greenhouse is not just a way to fill your kitchen with freshness, it brings both colour and flavour to your kitchen and barbeque all summer long. By selecting the right varieties, providing proper care, and harvesting your own fruits regularly, you can enjoy a bumper crop all summer and into autumn.  


Images courtesy of Robert Smith and Darren Lakin

Om Robert Smith

Rob is a seasoned gardener, specialising in growing edible plants. Not only does he write for multiple national Gardening Magazines, but he also appears now and again on TV and radio, sharing his passion for the “Grow Your Own” lifestyle on social media (@robsallotment).  Alongside his public persona, Rob also works with several of the counties best known gardening companies, including Suttons, Thompson & Morgan, Dobies, and The Organic Gardening Catalogue, to source new and exciting types of fruit, veg and flowers to be launched into garden centres across the UK and Europe.  At home you will find him in his Kitchen Garden, come rain or shine, accompanied by his faithful companions, Nipper and Reggie.

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