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Tomatoes

This Allotment Pro editorial draft summarises the cited RHS guide. Check the source and adjust timings for local conditions.
RHS source guide
Tomatoes crop illustration

Month by month

Sow

  1. Late February to mid-March

    sow indoors for greenhouse crops.

  2. Late March to early April

    sow indoors for plants that will crop outside.

Plant

  1. Early summer

    move well-rooted plants into their final position once temperatures remain above 16°C (60°F), hardening off outdoor plants first.

Harvest

  1. Mid-summer into autumn

    pick fully coloured fruits individually; greenhouse plants usually start earlier and continue longer than outdoor plants.

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1 - Getting Started

Tomatoes, Solanum lycopersicum, can be raised from seed or bought as young plants, then grown in greenhouse borders, open ground, growing bags or large pots. A greenhouse usually brings an earlier, larger crop. Outdoors, these tender plants need the warmest sunny and sheltered position available, protection from frost and reliably moist roots.

Tomatoes are close relatives of potatoes and outdoor plants are similarly vulnerable to blight, although greenhouse crops are affected less often. The wide choice includes tall cordons, compact bushes, dwarf plants and trailing basket forms, with fruit ranging from prolific cherries to plum, salad and large beefsteak types. Small-fruited cultivars tend to crop fastest and most freely.

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2 - Choosing What To Grow

Cordon, or indeterminate, tomatoes grow vigorously upwards. They occupy little ground space but require tall supports, regular tying and removal of side-shoots. Bush, or determinate, tomatoes stay more compact; trailing bushes suit windowboxes and hanging baskets. Bush side-shoots are retained, although fruit-laden stems may need short canes.

Choose for the growing site as well as flavour and appearance. Fruits may be red, purple, pink, orange, yellow, green or striped, and may be round, pear-shaped, elongated, smooth or deeply ribbed. Seed catalogues offer both long-grown heirlooms and modern disease-resistant cultivars. Young plants save time and space but provide less choice; grafted plants cost more but can be more vigorous, earlier, higher yielding and more disease resistant.

Recommended varieties

Cristal illustration

Cristal AGM

An early cordon salad tomato for reliable crops of tasty red fruit, with reasonable disease resistance. It is best under glass but can grow outside in a sheltered sunny position.

Cultivar sourceAllotment Pro variety guide
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3 - Sowing

Sow indoors from late February to mid-March for greenhouse cropping, or from late March to early April for outdoor plants. Use modules, small pots or trays and provide about 18°C (64°F), either in a heated propagator or on a warm windowsill under a clear cover. Seedlings usually emerge within a fortnight; uncover them promptly and give maximum light to prevent weak, leggy growth.

Pricking out and potting on

After a couple of weeks, when seedlings have two true leaves, move them individually into pots or modules of peat-free multi-purpose compost. Lift by supporting the rootball and hold each plant by a leaf, never its fragile stem. Replant leggy seedlings deeply so the first leaves sit just above the compost. Keep them bright, regularly watered and at least 16°C (60°F). They should be ready for their final position after about a month.

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4 - Planting

Plant well-rooted tomatoes in early summer once temperatures remain above 16°C (60°F). Harden outdoor plants off first. Set each plant deeply with its first leaves just above the surface, allowing the buried stem to form additional roots.

Planting in containers

Use peat-free loam-based or multi-purpose compost. Put one plant in a 30–45cm (12–18in) pot, or two in a standard growing bag. Bushes suit patio pots, troughs, windowboxes and baskets. Give cordons a tall cane or a slack vertical string anchored beneath the rootball; shelter pots against a sunny wall so top-heavy plants are less likely to blow over.

Planting in the ground

Choose rich, moisture-retentive but free-draining soil, adding plenty of garden compost, or plant through an organic mulch in a no-dig bed. Use the warmest sunny site, sheltered from wind, and space plants 45–60cm (18–24in) apart according to cultivar size. Insert cordon supports at planting. Avoid using the same bed in consecutive years so soil-borne disease does not build up; greenhouse ring culture is another option.

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5 - Plant Care

Watering

Keep soil or compost evenly moist. Fluctuation encourages fruit splitting and blossom-end rot, while curling leaves may signal drought. Containers can need daily watering in hot weather. For ground plants, sink a 15cm (6in) pot beside each plant and water into it, directing moisture toward the roots without leaving the stem base wet and prone to rot.

Feeding

Once the first fruits swell, feed container plants every 10–14 days with an organic high-potassium liquid fertiliser. Enriched ground may supply enough nutrients, although a fortnightly feed can increase yields.

Mulching

Cover ground or greenhouse borders with a thick layer of garden compost or well-rotted manure to conserve moisture and suppress weeds. Leave a clear gap around each stem to prevent rotting.

Improving pollination

Open greenhouse vents so pollinating insects can reach the flowers. Lightly tapping or shaking fully open blooms helps transfer pollen within them, and misting the flowers can also assist.

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6 - Pruning And Training

Train cordons as one tall stem, removing side-shoots regularly and attaching the main stem to a strong cane or winding it gently around a vertical string. Once a plant reaches its support or has set seven fruit trusses indoors or four outdoors, remove the main growing point two leaves above the top truss.

Side-shoots arise in the angle above each leaf. Check when watering and pinch or snap them off before they turn into unsupported leafy stems that consume space and reduce fruiting. Do not remove bush-tomato side-shoots; instead, add short canes wherever a heavy branch begins to droop.

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7 - Harvesting

Fruit begins ripening from mid-summer, with timing influenced by cultivar, weather and fruit size. Cherries usually ripen before large beefsteaks, and greenhouse plants generally crop earlier and later. Check every few days and pick each tomato fully coloured and ripe, keeping its stalk attached.

At season’s end, lift outdoor plants with unripe fruit and lay them on straw beneath cloches, or bring the fruits into a warm dark place. Keeping green tomatoes with a banana can help them ripen.

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8 - Problem Solving

Warm summers and even moisture favour trouble-free fruiting. Poor conditions can cause physiological leaf, stem and fruit symptoms, while fungi and sap-feeding insects may also attack. Good ventilation, crop rotation, consistent watering and regular inspection reduce risk.

Common problems

Tomato blight

Warm wet weather can bring a rapidly spreading disease that rots foliage and fruit. Remove affected material promptly and reduce conditions that keep outdoor leaves wet.

Problem source

Tomatoes: fruit ripening problems

Uneven colour, greenback and other ripening faults are often linked to preventable growing stresses. Match warmth, light, water and feeding to the plant’s stage.

Problem source

Tomatoes: fruit splitting and cracking

Late-summer fruit may split when moisture fluctuates and rapid water uptake stretches the skin. Maintain steady moisture and harvest ripe fruits promptly.

Problem source

Tomatoes: leaf problems

Leaf curling, discolouration and distortion can have environmental, nutritional, pest or disease causes. Inspect the whole plant and its recent growing conditions before acting.

Problem source

Tomatoes: stem problems

Tomato stems can develop harmless root initials as well as cracks, rots or other symptoms. Support plants, avoid stem-base saturation and identify the symptom before treatment.

Problem source

Grey mould

Botrytis cinerea causes soft decay with fuzzy grey growth, especially where humid air and damaged tissue coincide. Ventilate under cover and clear infected material.

Problem source

Glasshouse whitefly

Whiteflies feed on sap beneath greenhouse leaves and excrete sticky honeydew that can support sooty mould. Inspect leaf undersides and use non-chemical controls early.

Problem source