When to Plant Tomatoes
Tomatoes need warmth, strong light and protection from frost, so timing is crucial in the UK. Sow indoors in spring, then plant outside only after the local risk of late frost has generally passed, usually late May or June. Greenhouse and polytunnel growing allows earlier planting, but plants still need gentle acclimatisation.
Sow tomatoes indoors from late February to early April, depending on your light levels and where you intend to grow them. In a heated greenhouse or bright conservatory, an earlier sowing can be practical; on an ordinary windowsill, March is often safer because days are brighter. Sow one or two seeds per module in fresh peat-free seed compost, cover lightly and keep warm until germination. Once shoots appear, move them into the brightest available place so stems remain sturdy. Do not sow extremely early in the hope of an earlier crop. A large, leggy tomato held indoors for weeks is harder to manage than a compact plant sown later. Label varieties and dates before the trays become crowded.
Pot seedlings on when roots reach the edge of their module and plants have developed true leaves. Hold each seedling by a leaf and move it into a slightly larger pot of peat-free multipurpose compost. Tomatoes can be set a little deeper at this stage, covering part of the stem to encourage a strong root system. Water gently, then provide maximum light and moderate warmth. Repeat potting on only when needed; an oversized pot can stay cold and wet around a small root ball. Turn windowsill plants regularly and avoid leaves pressing against cold glass overnight. Begin checking the forecast from late April onwards, but treat it as guidance, since sheltered city gardens and exposed allotments warm at very different rates.
For greenhouse or polytunnel tomatoes, planting can often begin in April or May once night temperatures are consistently suitable and the structure is frost-free. Warm the soil or compost naturally by keeping the greenhouse closed on sunny days, but ventilate it well to prevent excessive heat and humidity. Plant one tomato per large container, growbag position or prepared greenhouse border, allowing sufficient space for air movement. Water the planting hole first, set plants slightly deeper than their pot level and firm them in. Insert canes, strings or other supports at planting time for cordon varieties. Keep fleece or temporary protection available for an unusually cold night, especially in an unheated greenhouse. Do not rely on daytime warmth alone when deciding to plant.
For outdoor tomatoes, wait until after the last spring frost has generally passed. This is commonly late May in milder southern gardens and often June in cooler northern, Scottish, Welsh or exposed areas. Harden plants off over one to two weeks first, starting in sheltered shade and gradually increasing their time outside. Choose a sunny, sheltered position with good airflow, such as against a warm wall or in a large container on a patio. Prepare soil with garden compost, but avoid overfeeding before flowers form. Plant on an overcast, calm day where possible, water thoroughly and protect plants with fleece or a cloche if a cold snap follows. Cold soil can stall growth even without a visible frost.
Space tomatoes according to their variety and final method. Bush tomatoes need room to spread, while cordon types can be trained vertically on sturdy supports. In containers, use fresh peat-free multipurpose compost and select pots at least 30 cm wide and deep. Water regularly at the base, checking daily in hot or windy weather. Irregular watering is a common cause of poor growth and fruit problems. Once the first flowers are forming and plants are established, begin a regular, light feeding routine according to the feed label. Remove only the side shoots of cordon varieties if you are training them as a single stem; bush types normally need their side shoots. Keep leaves dry where possible and ventilate greenhouse plants well.
Continue to judge timing by conditions rather than dates alone. If a late cold spell is forecast, cover outdoor plants before evening or move container tomatoes into a greenhouse, porch or sheltered spot. If plants become pale and still after planting, check cold, wind, water and root restriction before adding feed. Pick fruit as it colours fully, and remove damaged leaves or fruit promptly. Towards late summer, shelter can help remaining fruit ripen, but avoid sealing plants in humid, stagnant air. At season's end, clear plants and compost healthy material where appropriate. Record your sowing, planting and first harvest dates to refine timing for your particular garden next year.
Frequently asked questions
When can tomatoes go outside in the UK?
Plant outdoor tomatoes only after the local risk of late spring frost has generally passed, often late May in milder southern gardens and June in cooler or exposed areas. Harden plants off for one to two weeks first. Keep fleece or a cloche ready if an unexpected cold spell is forecast.
Can I plant tomatoes in an unheated greenhouse early?
Yes, usually in April or May if night conditions are reliably mild and the greenhouse remains frost-free. Harden plants off first, use fresh compost or prepared soil and keep temporary fleece available. Ventilate on sunny days, because a greenhouse can overheat quickly even when nights are cold.
Why are my tomato plants not growing after planting out?
Cold soil, wind, uneven watering and root disturbance commonly slow newly planted tomatoes. Protect them from chilly nights, water at the base and avoid overfeeding stressed plants. Once temperatures rise and roots settle, healthy plants usually resume growth. A sheltered sunny position makes a significant difference.
General guidance for UK home gardens and allotments. Conditions vary by region, soil and season; the RHS or a local garden centre can give site-specific advice. Page updated 19 Sep 2026.