What to grow in a greenhouse

Choose by outcome, not by catalogue size

A greenhouse is most valuable when it solves a specific growing problem: an earlier start for hardy seedlings, a more reliable summer crop of tomatoes and cucumbers, or a sheltered finish for autumn salad leaves. It is less useful as a place to squeeze in every attractive packet. In a small house, one overgrown cucumber can shade several pepper pots and turn the path into a daily obstacle.

Begin with the growing calendar and a sketch of the interior. Mark beds, pots, staging, the door and every vent. Then allocate each season's crops. The RHS notes that even a small unheated greenhouse can extend the season, but timing and the kind of crop still govern the result.

Spring nursery crops

The greenhouse can shelter hardy vegetable seedlings destined for outdoor beds: lettuces, brassicas, onions, leeks and peas are among the RHS examples. Clean modular trays make the space flexible because plants can leave as soon as outdoor conditions and hardening off allow. A sowing bench should not be treated as permanent storage for plants that have already outgrown their cells.

Tender seed such as tomatoes or peppers may need controlled warmth to germinate, especially early in the year. A sunny greenhouse alone does not guarantee a suitable night temperature. Start those seeds where the temperature and light work, then move them under glass when the growing-on environment is safe. Our seed-starting guide separates germination from planting out.

Tomatoes: high reward, regular attention

Tomatoes are the obvious summer greenhouse crop because shelter and warmth can make cropping more reliable. They also demand routine work: substantial root space, supports, watering, feeding, ventilation and frequent harvest. Tall cordon types use vertical space efficiently if there is a secure support and side shoots are managed. Bush types are simpler to prune but still need a suitable footprint.

Do not count a seedling tray as the final layout. Work out how many full-grown plants can be reached and watered without crowding the door or roof vent. The greenhouse tomato guide covers the full sequence, including containers and fruit problems.

Cucumbers and other climbing crops

Greenhouse cucumbers can be productive but need warmth, water, a strong vertical support and enough room for large leaves. Variety matters: choose one recommended for greenhouse cultivation and follow its fruiting and training instructions. The plant's height and leaf area may make it a poor neighbour for several short crops in a very narrow house.

Melons, climbing beans and other adventurous choices can work in the right conditions, but they are not effortless substitutes for tomatoes. Consider whether you can support and train the plant, provide its preferred environment and clear enough space for the full season. A crop that blocks a vent is costing more than its floor area suggests.

Peppers, chillies and aubergines

These tender crops can fit in containers and may suit gardeners who want a more varied harvest than several tomato plants. They still need warmth, good light and regular water. Starting them early can be sensible only with a suitable propagation and growing-on plan. In a cool summer, their progress may be slower than a packet illustration implies.

Containers offer layout flexibility, but the compost volume must match the mature plant. A very small pot dries quickly in a hot greenhouse and restricts roots. Group crops with similar watering needs, and keep them clear of the door's swing and the daily path.

Salads, herbs and useful short crops

Lettuce, spicy leaves, pea shoots and some herbs can occupy pockets of space before or after the main summer planting. Basil likes warmth and can be grown on under cover; hardy herbs have different needs and may prefer to avoid midsummer greenhouse heat. A shallow tray of leaves is not a permanent underplanting solution if a mature tomato later shades it completely.

The RHS suggests late-summer sowings of salad leaves and baby carrots where space allows. For the dark part of winter, establish hardy lettuce and pea shoots earlier rather than expecting rapid growth from a December sowing. Succession is a better productivity strategy than one enormous sowing.

Match crops to greenhouse format

A mini greenhouse or wall growhouse excels at raising trays and protecting compact pots, but it rarely has the height, air volume or root area for several full-size cordon tomatoes. A 6 × 4 walk-in may support a small deliberate crop mix. A 6 × 8 gives more flexibility for a central path, staging and tall plants, though vents and water access still matter.

If you have not chosen a structure, compare greenhouse sizes against the crops you actually want to grow. The best greenhouse is one that can hold the mature planting plan, not merely the spring trays.

Plan water, supports and airflow together

Set strong supports before a climbing crop fills the space. Clips or ties secure stems to a support; they do not anchor that support to the greenhouse. Use manufacturer-approved frame attachments, or a separate sound cane or trellis system. Check ties as stems thicken.

Place water at the root zone and inspect pots in hot weather. Drip lines can help with a row or a collection of containers, but the layout, pressure and water supply must be appropriate. Read the watering-systems comparison before choosing a timer. Leave air around foliage and keep vents moving freely; cramped plants are harder to monitor for pests.

What not to force into the greenhouse

Many hardy crops grow well outdoors after a protected start and need not occupy valuable summer floor area. Conversely, heat-loving plants can fail if the structure is too cold at night. A greenhouse cannot erase the plant's biology. Identify the benefit you expect from covering each crop and free the space when that job is done.

Keep a short record of variety, sowing period, final position and harvest. The next year's choices should reflect what your garden actually produced and what you enjoyed eating. If whitefly or other pests affected a crop, note that too and review the pest guide before repeating the same dense arrangement.

Sources and related reading

Crop and seasonal examples follow the RHS guide to growing vegetables in greenhouses. For crop-specific timings and culture, start with the relevant RHS plant guide and the seed packet rather than treating a broad crop list as a fixed planting schedule.