Growing Tomatoes in Grow Bags on a Patio

Why Grow Bags Suit a Paved Patio

Not every grower has a vegetable patch, and a patio of slabs or gravel can feel like a dead end for raising your own food. Grow bags change that. A standard bag holds roughly 30 to 40 litres of compost, sits flat against a wall or fence, and demands no digging, no raised bed and no permanent footprint. When the season ends, you tip the spent compost onto the flower border and fold the bag away for next year.

Tomatoes happen to be one of the best crops for this treatment. They are hungry, thirsty and perfectly content in a confined root run, provided you keep water and nutrients coming steadily. The secret is to treat the bag as a proper growing container rather than a plastic sack you happen to have planted into. Do that, and a modest sunny corner will comfortably crop more tomatoes than a household can eat.

Choosing Compact Varieties

Variety choice matters more than anything else on a patio. Tall cordon types will grow perfectly well in a bag, but they need staking and can reach well over a metre, which soon looks untidy in a small space. Look instead for compact and bush varieties bred for containers.

• 'Tumbling Tom' is the classic trailing cherry, cropping red or yellow on plants that spill attractively over the bag edge.
• 'Hundreds and Thousands' produces masses of tiny, sweet fruit on a plant that stays manageable.
• 'Red Alert' and 'Vilma' are compact bush types that need little or no pinching out.
• 'Totem' is a short cordon that fruits reliably outdoors in a British summer.

Cherry varieties generally ripen faster and more dependably than large beefsteak types, which want more heat and a longer season than most patios deliver.

Planting Up: Compost, Drainage and Spacing

Don't rush the planting date. Wait until late May or early June in most of the UK, once nights have warmed, and harden plants off gradually first. Choose a spot in full sun — six hours or more — and ideally against a south-facing wall that will hold warmth into the evening.

Before planting, shake the bag to loosen the compost and cut three or four drainage slits along the base, away from the sun. Sinking bottomless pots or ring-culture collars into the bag gives roots more depth and makes watering far more efficient. Plant two cordon tomatoes or three bush types per bag, spaced evenly. Bury each stem up to the first set of leaves, as tomatoes will root along it, and water in thoroughly.

Watering: Little and Often Beats a Flood

This is where most patio crops fail. A grow bag holds a small volume of compost and dries out alarmingly fast. In warm weather, check morning and evening, and on a hot day a bag in full sun may need watering twice.

Aim for consistently moist compost, never sodden. Irregular watering is the main cause of blossom end rot — the sunken brown patch on the base of the fruit — which is a calcium uptake problem triggered by fluctuating moisture, not by a shortage in the compost. Push a finger two or three centimetres in to judge before reaching for the can. A tray beneath the bag can help on hot days, but never leave plants standing in water. A mulch of gravel or grass clippings slows evaporation noticeably.

Feeding: When Tomatoes Start to Earn Their Keep

Bag compost carries enough nutrients for roughly six weeks. After that, the plants rely on you. Begin feeding when the first truss of flowers has set fruit, using a high-potassium tomato feed diluted as directed — once a week at first, rising to twice weekly once plants are cropping heavily.

Feed too early and you will get lush leaves and precious little fruit. Always water before you feed, so you don't scorch dry roots, and never top up a starving plant with a double-strength dose.

Supporting, Pinching Out and Ripening

Cordon types need a sturdy cane pushed into the bag beside the stem, tied in with soft string every 20 centimetres or so. Bush types need almost nothing, though a short cane helps against wind.

Pinch out the side shoots on cordons — the small shoots in the angle between leaf and main stem — once a week. Leave bush varieties alone. Remove the leaves below the first truss once fruit has set, which improves airflow and helps deter disease. In late August or early September, pinch out the growing tip two or three trusses above the last set fruit, so the plant's energy goes into ripening what is already there.

Towards the end of the season, ease off the watering and clear any leaves shading the fruit. Green tomatoes will ripen indoors on a sunny windowsill, or in a paper bag with a ripe banana to speed things along. However good the summer, there is always a final bowlful to coax along in the kitchen.