How to Grow Strawberries in a Greenhouse

Introduction

There are few things more quintessentially British than the taste of a freshly picked strawberry. But why wait until late June for that first bite? In our 16+ years helping UK gardeners, we’ve found that growing strawberries under glass is one of the most rewarding ways to utilise your greenhouse.

By bringing your plants indoors, you aren't just protecting them from the unpredictable British weather; you are manipulating the seasons. With the right technique—known as "forcing"—you can enjoy sweet, juicy fruit as early as May.

However, it’s not quite as simple as putting a pot on a shelf and forgetting about it. Greenhouse strawberries require a specific rhythm of care, particularly during the winter months. In this guide, I’ll walk you through exactly how to prepare, plant, and care for your crop to ensure a bumper harvest.

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Why Grow Strawberries in a Greenhouse?

While strawberries thrive in outdoor beds, moving them into one of our aluminium greenhouses offers distinct advantages that justify the extra pot work.

1. Earlier Harvests: As mentioned, you can advance cropping by up to a month.
2. Pest Protection: Keeping plants off the ground and behind glass protects them from slugs, snails, and birds that decimate outdoor crops.
3. Clean Fruit: Hanging baskets or staging prevents soil splash, meaning you don't have to wash grit off your fruit before eating.
4. Climate Control: You can maintain the optimal temperature for ripening, leading to sweeter fruit with higher sugar content.

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Choosing the Right Variety

Not all strawberries are created equal. When growing under glass, you generally want "Early" varieties to make the most of the protection, or "Everbearers" for a long season.

Here is a breakdown of the varieties that perform best in UK greenhouse conditions:

Variety Category	Recommended Strain	Best For	Harvest Window (Greenhouse)
Early Season	Honeoye	High yields and disease resistance.	Early May - June
Mid-Season	Cambridge Favourite	The reliable classic. Great flavour.	Mid May - June
Early Season	Elsanta	Supermarket favourite, stores well.	Early May - June
Everbearing	Flamenco	Long harvest period.	June - September
Alpine/Wild	Mignonette	Small, intense flavour. Shade tolerant.	June - October

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The Winter Strategy: Chilling and Forcing

This is the section most beginners miss. You cannot simply keep strawberry plants in a warm greenhouse all winter and expect a great crop. According to horticultural data, strawberries require a "chill period" of roughly 200 to 400 hours below 7°C to break dormancy effectively. Without this, yields drop significantly.

Step 1: Winter Preparation (December - January)

If you have existing plants in pots, leave them outside or in a cold frame during early winter. They need to feel the cold. If you are buying bare-root runners now, pot them up but keep them cool.

This is where a cold frame becomes an invaluable tool. It protects the roots from freezing solid but ensures the foliage gets the necessary chill hours.

Step 2: The "Forcing" Phase (February)

Once the plants have had their winter rest, it is time to wake them up.

1. Bring them in: In mid-February, move your pots into the greenhouse.
2. Clean up: Remove any dead or brown leaves from the winter to improve airflow.
3. Gradual Warmth: If you have a heated greenhouse, aim for 10°C initially, rising to 15°C as leaves develop. If unheated, the natural solar gain will still wake them up weeks earlier than outside.

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Potting and Soil Requirements

Strawberries are hungry plants, but they hate having "wet feet." The preparation you do in your potting sheds before bringing them into the greenhouse is critical.

The Mix

Use a high-quality general-purpose compost mixed with 20% perlite or grit. Strawberries prefer a slightly acidic soil (pH 6.0–6.5), so avoid adding lime.

Pot Size

• Single Plants: A 3-litre pot (approx 15cm diameter) is ideal.
• Grow Bags: You can fit 6-8 plants in a standard grow bag.
• Hanging Baskets: A 30cm basket can hold 3-4 plants comfortably.

Warning: Do not bury the crown. The "crown" is the central point where stems emerge. If you bury it, it will rot. If it's too high, the roots dry out. It must sit exactly at the surface level.

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Care and Maintenance: The "Greenhouse Routine"

Growing under glass requires you to be the provider of everything nature usually supplies.

Watering

In a greenhouse, pots dry out fast. Check them daily. Water in the morning so the foliage dries before nightfall—this reduces fungal issues. Crucially, water the soil, not the leaves.

Feeding

Once you see the first flowers opening, begin feeding. Use a high-potash liquid feed (tomato feed is perfect) every 7–10 days. This encourages fruit production rather than leafy growth. This is a similar schedule to when to plant tomatoes in an unheated greenhouse, making them good rotation partners.

Temperature Control

Strawberries do not like extreme heat. If your greenhouse soars above 25°C in late spring, the fruit can become soft and mushy. Utilise your roof vents and louvres. If you are growing in a small greenhouse, keep the door open on sunny days to maintain airflow.

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The Pollination Challenge

This is the most common reason for failure in greenhouse strawberries. Outside, wind and bees pollinate the flowers. Inside a closed greenhouse in March or April, those insects are absent.

The Symptom: Misshapen, lumpy, or very small fruit.
The Fix: You must be the bee.

How to Hand Pollinate:

1. Wait until midday when the pollen is dry and "fluffy."
2. Use a soft artist's paintbrush or a rabbit's tail.
3. Gently brush the centre (yellow part) of every open flower, transferring pollen from one flower to another.
4. Repeat this every 2 days until flowering finishes.

According to RHS research, poor pollination is the leading cause of fruit deformation in protected crops, so do not skip this step!

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Troubleshooting Common Problems

Greenhouse environments are great for plants, but also great for pests.

Problem	Symptoms	Solution
Red Spider Mite	Yellow mottling on leaves, fine webbing.	Mist foliage regularly (they hate humidity). Introduce biological control Phytoseiulus persimilis.
Botrytis (Grey Mould)	Grey fuzzy mould on fruit or stems.	Reduce humidity. Remove infected material immediately. Water only at the base.
Slugs/Snails	Holes in leaves and eaten fruit.	Check under pot rims. Use copper tape around pots. Handpick at night.
Vine Weevil	Plant suddenly collapses; white grubs in soil.	Use parasitic nematodes (Steinernema kraussei) in late summer/autumn.

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Maximising Space: Vertical Growing

One of the great joys of a greenhouse is efficiency. Strawberries are compact, meaning they don't need to take up valuable staging space that you might need for seed trays.

• Shelf Edges: Place pots along the very edge of your staging. The leaves and fruit can hang over the side, receiving great light and airflow.
• Hanging Baskets: Utilise the roof bars. Just remember, baskets dry out faster than pots on the ground, so you may need to water twice daily in warm weather.
• Gutters: Some growers attach lengths of guttering to the greenhouse sides. This is an excellent way to grow dozens of plants in a "dead space," similar to techniques used for how to grow mushrooms in a greenhouse under benches.

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Summary

Growing strawberries in a greenhouse is a fantastic way to bridge the "hungry gap" of late spring. By selecting the right early varieties, giving them a winter chill, and hand-pollinating diligently, you can enjoy bowls of red, sweet fruit while your neighbours are still looking at green leaves.

If you are ready to start your forcing journey, check out our range of cold frames and shelving to get your setup ready for the coming season.