Allotment Greenhouses in February: What to Sow, Grow and Prepare

An allotment greenhouse earns its space long before the summer tomatoes arrive. In February, it provides somewhere sheltered to prepare seed trays, start suitable crops and protect overwintering plants while the outdoor growing season slowly gets moving.

However, growing under cover in February takes a little judgement. A greenhouse can feel surprisingly warm on a sunny afternoon and become freezing cold overnight. Successful early growing depends on matching your crops to the conditions you can provide.

This guide explains how to use an allotment greenhouse in February, including cleaning, sowing, watering, frost protection and planning for harvests later in the year. Whether you have a small glasshouse or a larger growing space, the aim is healthy plants rather than the earliest possible sowing date.

What Can You Do in an Allotment Greenhouse in February?

February is useful for both preparation and carefully chosen sowings. Your priorities should be to:

• Clean glazing so plants receive as much daylight as possible.
• Check doors, vents, glazing clips and fixings.
• Remove dead plant material and inspect overwintering plants.
• Organise pots, labels, seed trays and compost.
• Monitor daytime and overnight temperatures.
• Start appropriate hardy crops when conditions allow.
• Provide warmth for tender crops that need it.
• Plan how the space will be used through spring and summer.

Avoid filling every available surface with seed trays immediately. Each successful sowing eventually needs more room, particularly once seedlings are moved into individual pots.

A little spare space makes it much easier to care for plants properly.

Understand the Limits of an Unheated Greenhouse

An unheated greenhouse offers shelter from wind and heavy rain, but it does not guarantee frost-free conditions.

Sunshine can warm the enclosed air during the day. After sunset, that warmth is lost, and temperatures inside may fall close to those outside. Tender seedlings can therefore suffer even when they looked perfectly comfortable earlier.

Use a maximum–minimum thermometer at approximately plant height, away from direct sunlight. Check the overnight minimum regularly rather than relying on how warm the greenhouse feels during a visit.

For an exposed allotment in Sheffield or another colder location, early sowings may need to wait longer than those in a sheltered southern garden.

Seed packets provide useful temperature guidance. Follow the requirements of the crop and variety rather than treating February as a fixed instruction to sow.

Clean Your Greenhouse Before Spring Gets Busy

Dirty glazing reduces the light reaching plants at a time when daylight is already limited. Cleaning also gives you a chance to spot damage before the structure becomes crowded.

Choose a mild, calm day. Move plants somewhere sheltered while you work, keeping tender plants protected from cold.

Brush away loose debris, then wash accessible glazing and framework with warm water and a soft brush or sponge. Clean staging and remove accumulated compost from corners.

Warm water is generally sufficient for greenhouse surfaces. Pots and propagation equipment can be scrubbed with warm soapy water, then rinsed. Only use specialist cleaning products according to their instructions. RHS Advice

Check gutters and downpipes while you are there. Remove leaves that prevent rainwater reaching your water butt.

Never lean against glazing or reach across a greenhouse roof. Use suitable equipment and professional help for damaged or inaccessible sections.

Check the Structure and Organise the Space

Winter weather can loosen glazing clips, damage panels and affect door runners. Small repairs are easier before spring growth restricts access.

Check that:

• Glazing is secure and damaged panes are dealt with safely.
• Doors close properly.
• Vents open and shut.
• Shelving and staging remain stable.
• Paths are clear.
• Water containers have secure lids.
• Pots cannot easily fall onto plants below.

Group plants according to their needs. Keep regularly watered seedlings accessible, while dormant plants that need little moisture can occupy a separate area.

Leave space between pots wherever possible. Crowded plants are harder to inspect, and overlapping foliage restricts airflow.

Keep a notebook or simple sowing record nearby. Recording varieties and dates helps you judge which early sowings were worthwhile when you plan next year.

What to Sow in an Unheated Greenhouse in February

Hardy crops are usually the most practical starting point, but even these need suitable compost temperatures and protection from severe weather.

Broad Beans

Broad beans can be started in deep modules or individual pots when conditions suit the variety.

Use containers with drainage holes and follow the seed packet for sowing depth. Water after sowing, then avoid keeping the compost saturated.

Protect seeds from mice, which can quickly clear a tray. Check emerging plants regularly and give them good light.

Before planting outside, gradually acclimatise them to outdoor conditions. Do not plant into frozen or waterlogged ground.

Peas

Early peas can be started under cover in deep modules or clean guttering with drainage holes. This allows plants to establish before moving into a prepared outdoor bed.

Choose a variety recommended for early sowing and protect the seed from rodents. The RHS includes greenhouse pea sowing among its February vegetable jobs. rhs.org.uk

Avoid allowing roots to become tightly congested while waiting for suitable planting weather. A modest first sowing is easier to manage than several trays that all need planting together.

Lettuce and Hardy Salad Leaves

Suitable lettuce varieties and hardy salad crops can be tried under cover, particularly as conditions improve towards the end of the month.

Check the packet carefully: varieties differ in their suitability for cool conditions.

Sow small amounts rather than a large tray of everything. Later sowings can follow as light levels and temperatures improve.

Mustard leaves, mizuna and other suitable salads may provide useful options, but growth will depend on your local conditions.

Radishes and Early Carrots

In a sheltered greenhouse, small trial sowings of suitable radishes or early carrots may be possible in prepared soil or sufficiently deep containers.

Compost or soil needs to be workable and warm enough for germination. Cold, wet conditions can cause disappointing results.

Carrots are best sown where they will grow rather than transplanted from ordinary seed trays. Choose a variety suited to the available container depth.

Treat these as early experiments rather than guaranteed crops.

Can You Sow Tomatoes, Chillies and Aubergines in February?

Yes, but these tender crops need more than an unheated greenhouse.

They require appropriate warmth for germination, followed by bright conditions and suitable temperatures as seedlings develop. A heated propagator may start them successfully, but the young plants still need somewhere suitable afterwards.

The RHS lists sowing tender greenhouse crops from mid-February onwards. For an allotment grower, the deciding factor is whether you can maintain the necessary conditions beyond germination. rhs.org.uk

Chillies and aubergines can benefit from a long growing season. Tomatoes often become difficult to manage if started too early without enough light or space.

If your greenhouse is unheated and you have no bright, warm growing area, delaying sowing can be the better option. Compact, healthy plants are more useful than tall, weak seedlings produced simply to get an early start.

Cucumbers grow quickly and dislike cold conditions, so there is usually little advantage in rushing them for an unheated greenhouse.

Protect Plants from Frost

Keep horticultural fleece available for vulnerable plants during cold spells. Support it where practical and remove or adjust it when conditions improve.

A smaller protected area inside the greenhouse can be easier to manage than trying to warm the entire structure. However, fleece and insulation provide limited protection; neither guarantees survival in a hard freeze.

If using greenhouse insulation, balance heat retention against the need for light. Keep vents and doors usable.

Any heater must be suitable for greenhouse conditions and permitted by your allotment rules. Electrical equipment needs a safe, appropriate supply and installation.

Do not use barbecues or improvised fuel-burning heaters inside an enclosed greenhouse.

For many allotment growers, choosing hardy crops and delaying tender plants is the most practical approach.

Ventilate on Suitable Days

Keeping the greenhouse permanently shut can allow moisture to build up around plants.

On mild, sunny days, open a vent or door enough to encourage air exchange without exposing plants to a harsh draught. Adjust ventilation to the weather and close up before temperatures fall if frost-sensitive plants are inside.

The RHS specifically recommends February ventilation on sunny days to reduce the risk of fungal infections. It also stresses giving seedlings maximum available light to prevent weak growth. tender plants / RHS

Remove yellowing leaves and dead plant material promptly. Avoid leaving wet foliage pressed against glazing or neighbouring plants.

Automatic vent openers can be useful later in the season, but check their operation rather than assuming they are responding exactly as needed.

Water Carefully in February

Water according to the condition of the compost and the needs of the plant, rather than following a daily timetable.

Cool conditions and slower growth usually mean plants use less water than in summer. Nevertheless, small pots can dry out on bright days.

Check beneath the compost surface and lift containers to judge their weight. A light pot may need watering even if the top looks slightly damp.

Where possible:

• Water during the morning.
• Direct water towards the compost.
• Let excess water drain.
• Empty standing water from trays when appropriate.
• Keep dormant plants on a separate watering routine.

Seed compost should remain moist enough for germination without becoming waterlogged. Repeated heavy watering cannot compensate for unsuitable temperatures.

Look After Overwintering Crops

If you already have established salads or other suitable crops growing under cover, inspect them regularly.

Remove damaged foliage, check for slugs and look for aphids on sheltered new growth. Harvest lightly when plants are growing slowly, leaving enough healthy leaves for recovery.

Avoid assuming that every pale leaf needs fertiliser. Cold roots, wet compost and limited light can also affect growth.

Check the growing conditions first. Feed according to the crop and its stage of growth, rather than routinely applying strong feeds to every plant in February.

Prepare Greenhouse Beds and Containers

Remove old roots and plant debris before preparing the next crop.

For soil beds, assess drainage and soil condition. Where appropriate, add a modest layer of well-rotted compost. Avoid working wet soil until it becomes smeared or compacted.

For containers, clean out drainage holes and choose compost suited to the crop. Use fresh seed compost for propagation rather than taking old material from a previously cropped pot.

Check the volume of your summer containers now. Tomatoes and cucumbers need enough root space and a realistic watering arrangement.

Repeated problems in greenhouse soil deserve investigation. Adding more feed each year will not solve every issue with drainage, disease or nutrient balance.

Plan for Growing Beyond February

Think about the greenhouse as a space that changes throughout the year.

Choose crops that fit your available space and visiting routine.

Summer containers may need frequent attention during hot weather. Before planting, consider water access, ventilation and who can help when you are away.

Leave room for harvesting and maintenance. A greenhouse packed with plants can become much harder to manage than one with fewer, well-spaced crops.

Common February Greenhouse Mistakes

The most frequent problem is sowing more than the available conditions can support.

Other mistakes include:

• Assuming an unheated greenhouse cannot freeze.
• Providing germination warmth without a suitable growing area afterwards.
• Leaving seedlings in poor light.
• Keeping compost constantly wet.
• Failing to ventilate during suitable weather.
• Allowing plants to outgrow their containers.
• Starting too many trays before planning their next stage.

A later sowing that grows steadily can catch up with an earlier one held back by cold or inadequate light.

Frequently Asked Questions

Is an unheated greenhouse useful in February?

Yes. It provides shelter for preparation, suitable hardy sowings and established crops. Its usefulness depends on local weather, light and the plants you choose.

Should I water greenhouse plants every day?

Check them regularly, but water only when needed. Different plants and container sizes dry out at different rates.

Can I leave seedlings in the greenhouse overnight?

Only if overnight conditions suit the crop. Hardy seedlings and tender tomatoes have very different requirements.

Do I need to heat the whole greenhouse?

No. Many growers use an unheated structure successfully by choosing suitable crops. Tender early sowings need a reliably warm growing area, which may be elsewhere.

What is the best February greenhouse job?

If the structure needs attention, cleaning and repairs are a useful starting point. A sound greenhouse with clean glazing gives later sowings a better environment.

Make February a Useful Starting Point

February greenhouse growing is about making sensible preparations and starting crops you can care for properly.

Clean the glazing, monitor temperatures, organise the space and sow manageable quantities. Let your local conditions guide the pace.

A few healthy trays and a well-prepared greenhouse can provide a stronger start than a structure overflowing with seedlings that have nowhere suitable to grow.

Keep smiling, keep shining, keep gardening with Ben.