How to Grow Tomatoes in the UK: Outdoors, Indoors, and Everything In Between

All tomato varieties fall into one of two growth habits, and confusing them leads to poor results. Determinate (bush) varieties grow to a fixed height — typically 60–90 cm — set their fruit within a defined period, and stop growing once the terminal flower truss forms. They do not require pinching out of side shoots, are well-suited to growing in containers without tall support, and produce their crop over a relatively concentrated window of 3–4 weeks. For UK outdoor growing, determinate varieties are often the more pragmatic choice because they ripen their fruit before the late blight season (which typically peaks in July and August). Varieties such as Tumbler, Tornado, and Roma are reliable determinate choices for outdoor UK growing. Indeterminate (cordon) varieties continue growing upwards indefinitely until stopped by frost or the gardener, can reach 1.8 m or more under glass, and produce fruit continuously throughout the season. They require regular pinching out of side shoots (laterals) and a single-stem training system with substantial support. Indeterminate varieties include the vast majority of heritage and greenhouse types — Gardener's Delight, Sungold, Ailsa Craig, Black Cherry, and the famous Moneymaker. These are the best choice for greenhouse growing where the season can be extended and height managed. For outdoor UK growing, choosing early-ripening indeterminate varieties — those that produce ripe fruit within 60–65 days of transplanting — gives the best chance of a meaningful harvest before blight arrives.

Tomatoes are warm-season crops that originate in the high-altitude valleys of the Andes — an environment with warm days, cool nights, strong sunlight, and low humidity. This could hardly be further from British conditions, particularly north of the Midlands. The key metric is accumulated heat units, expressed as growing degree days (GDD). Tomatoes require a minimum soil temperature of 10°C for root development and consistent air temperatures above 18°C for pollen viability — below this threshold, pollen becomes sterile and fruit fails to set. In the UK, outdoor conditions rarely exceed these thresholds before June, meaning effective outdoor growing is compressed into June–September in the South and June–August in the North. Indoor growing under glass or polycarbonate extends this window considerably — to April–October in a heated greenhouse, or May–October in an unheated one. The sowing and planting calendar for UK tomatoes is consequently very specific: sow indoors in heated propagators from late February (indeterminate greenhouse types) to late March (outdoor types), grow on under lights or on a bright south-facing windowsill, pot on as roots circle the base, and plant out only after the last frost date for your region (mid-May in the South, late May or even early June in Scotland and exposed Northern locations).

A greenhouse or polytunnel transforms tomato growing in the UK from a marginal to a reliable activity. The key benefits are not merely warmth — though that matters — but the ability to control humidity (opening vents and doors), the elimination of rain directly wetting the foliage (which is the primary driver of blight spread), and the extension of the season by 4–6 weeks at each end. Under glass, indeterminate cordon varieties trained up vertical strings tied to a horizontal wire at the roof ridge are the standard approach. A well-managed 2.4 m × 1.8 m lean-to greenhouse can comfortably house 4–6 cordon plants trained to 1.5 m, yielding 4–8 kg of fruit per plant in a good season. Outdoor growing is more exposed and the variety choice is more constrained (see above), but the flavour of a sun-ripened outdoor tomato is arguably superior — the slight temperature stress and ultraviolet light exposure of outdoor growing produces higher concentrations of lycopene and other flavour compounds. For outdoor growing, the best sites are south or south-west facing, sheltered from wind, against a wall (which stores daytime heat and re-radiates it at night), with well-draining soil amended with organic matter. Raised beds warm faster than in-ground soil and are strongly preferred in the UK.

Side shoots — also called laterals or suckers — emerge from the axils between the main stem and each leaf petiole on indeterminate tomato plants. If left unpinched, each side shoot will develop into a secondary stem with its own laterals, producing a sprawling, heavily foliaged plant that directs energy into vegetative growth at the expense of fruit development. In the UK's short season, this is doubly problematic: a plant with excessive foliage creates its own microclimate of still, humid air around the fruits — ideal conditions for blight spores to germinate and penetrate. Pinching out involves removing each side shoot when it is 2–3 cm long, either with the fingertip and thumb (a clean snap) or sharp scissors sterilised between plants to prevent disease transmission. The technique applies only to indeterminate varieties grown as cordons. For determinate bush varieties, removal of side shoots reduces the fruit yield and is not recommended. The one exception sometimes made even for indeterminate varieties is to allow a single side shoot to develop as an insurance growing point — if the main growing tip is damaged by pests, cold, or accident, the retained side shoot can be trained as a replacement main stem.

Potato blight (Phytophthora infestans) and its close relative tomato blight are the most devastating disease threats to UK tomato growers. The pathogen is not a true fungus but an oomycete — a water mould — and it thrives in the warm, humid conditions that characterise British summers from July onwards. Blight spores travel by wind and water splash; once they land on a leaf surface they can penetrate within 2–4 hours if conditions remain humid. Infection is characterised by dark, water-soaked patches on the leaves and stems, rapidly followed by white sporulation on the underside of affected tissue, and spreading to the fruit where it causes a brown, firm rot. The standard preventive spray for organic and conventional growers alike is copper fungicide (Bordeaux mixture or similar), which creates a hostile surface environment for spore germination. This is a true preventive — it must be applied before infection occurs, typically from mid-June onwards, and reapplied after rain. It does not cure existing infection. Beyond chemistry, cultural practices are the primary defence: maximum spacing between plants (at least 45 cm between plants, 75 cm between rows) allows air circulation that dries the foliage rapidly after rain; removing the lower leaves to 30–45 cm from the soil surface prevents rain splash from carrying soil-dwelling spores onto the plant; watering at the base rather than overhead avoids wetting foliage; and growing under cover eliminates the direct rain contact that is the primary transmission vector. Certain varieties carry partial resistance to blight — Ferline, Losetto, and Mountain Magic are the best-known blighty-tolerant varieties in the UK market, offering meaningful protection without eliminating the risk entirely.

Companion planting tomatoes with basil is one of the most consistently practised folklore remedies in kitchen gardening, and there is modest evidence to support it. Basil's volatile aromatic compounds — linalool, eugenol, and others — have been shown in laboratory conditions to repel certain aphid species and thrips. Whether this translates to a meaningful reduction in pest pressure in an outdoor garden is harder to demonstrate, but the practical reality is that basil is a warm-season herb that thrives in similar conditions to tomatoes, occupies the understorey without competing significantly for light, and makes excellent culinary use of the same space. The combination is therefore rational on multiple grounds. Blossom end rot is not a disease — it is a physiological disorder caused by calcium deficiency in the developing fruit tip. This is almost never caused by insufficient calcium in the soil; British soils are nearly universally calcium-adequate. The real cause is interruption of calcium transport, which moves into the plant with the water flow. Irregular or insufficient watering — allowing the compost or soil to dry out between waterings, or inconsistent irrigation — interrupts this flow and the rapidly growing fruit tip fails to receive adequate calcium, causing the cells at the base of the fruit to die and collapse. The solution is consistent, regular watering rather than infrequent large volumes. Container-grown tomatoes are dramatically more susceptible than ground-grown ones because compost dries much faster than soil. In hot weather, container tomatoes may need watering twice daily. Mulching the soil surface with 5–7 cm of well-rotted compost reduces evaporation and moderates soil temperature, substantially reducing blossom end rot incidence in outdoor beds.