Growing Tomatoes in Scotland: The Complete Guide

Solanum lycopersicum

Everything you need to grow tomatoes in Scotland, from a March sowing on a windowsill to the last green fruit ripening in a drawer in October. We have done the research so you don't have to.

Tomatoes reward getting a few decisions right early. Choose the wrong type and you will spend the summer fighting a plant that wanted to grow differently. Put them outdoors in the wrong part of Scotland and blight will take them in a wet August. Get the type, the position and the watering right and they are genuinely straightforward. A sun-warmed tomato picked in a Scottish polytunnel in August is one of the best things this climate produces.

Under glass or outside? Decide this first

In Scotland this is not a preference. It is the decision the whole crop turns on. A polytunnel, greenhouse or even a sunny porch gives you an earlier start, a longer autumn, warmer nights and, most importantly, dry leaves. Wind-blown blight spores need hours of wetness sitting on the leaf before they can infect, so a roof over the plants removes the single biggest reason Scottish tomato crops fail.

Outdoors, the picture varies sharply across the country. In the Central Belt and the sheltered south-west, a warm, sunny, wind-protected wall will ripen a bush variety in a decent summer. North of the Central Belt outdoor cropping is marginal, and at altitude it is unreliable enough that we would not plan a season around it.

Treat under cover as the default here, not an upgrade. Tomatoes are frost-tender and need warmth to ripen, and our wet summers are exactly what blight wants. Irish growers, in a similar Atlantic climate, are told much the same.

Cordon or bush

Every variety grows in one of two habits, and the choice changes what you do every week of the summer. Check the seed packet before you buy, because the two are not interchangeable.

• Cordon (indeterminate) is vigorous, tall and single-stemmed. It needs a tall support and its side-shoots removed all season. It takes up very little floor space, which suits a narrow greenhouse border or a growing bag against glass. Most of the best varieties are cordons.
• Bush (determinate) is naturally compact, and you leave the side-shoots alone. Far less work, and trailing types will grow in a windowbox or hanging basket. If you are growing outdoors in Scotland, or growing tomatoes for the first time, start here.

Varieties worth growing

Pick the variety before you sow: it settles the habit, the season length and how much work the plant will be. Every variety here carries the RHS Award of Garden Merit, a UK-wide award rather than a Scottish one; nobody trials tomatoes for Scottish gardens, which is the gap this site exists to close. The pick below is our judgement, reasoning shown.

Also worth considering

Favour early ripening and disease resistance over size and flavour ceilings. In a short season a beefsteak that needs another fortnight of warmth is a beefsteak you compost. Shirley and Gold Nugget sit alongside Sungold because they do different jobs: a dependable greenhouse cordon, and a bush that needs no side-shooting at all.

Sowing

Work backwards from where the plant will live. Sow about eight weeks before it goes into its final position, so the plant is ready exactly when conditions are. Irish growers work to the same interval in a near-identical climate.

• Greenhouse or polytunnel: sow around mid-March, for planting in early May.
• Outdoors: sow in early April, for planting in early June.

Those are Central Belt lowland dates. Further north, and at any altitude, both shift later. There is no advantage in going earlier than this. A tomato sown in January sits in poor light, grows thin and leggy, and is overtaken by a March sowing.

Seed needs around 18°C to germinate, so use a heated propagator or a warm windowsill, and cover the tray with a clear plastic bag to hold humidity. Seedlings usually appear within a fortnight. Uncover them the moment they do and give them the brightest position you have. This is where Scottish light levels start working against you, and leggy seedlings are almost always seedlings left covered and dim for a few days too long.

Pricking out and potting on

A couple of weeks after germination, once each seedling has its first pair of true leaves, move them into individual pots or modules of peat-free multi-purpose compost. Lift each one by a leaf rather than the stem, because a crushed stem is fatal and a torn leaf is not, and use a dibber to support the rootball as it comes out.

If a seedling has gone leggy, plant it deeper so the first pair of leaves sits just above the compost. The buried stem grows new roots and you recover a sturdy plant. Keep them at 16°C or above and water regularly.

Planting out

Plant into the final position once temperatures are reliably above 16°C. That word carries more weight in Scotland than almost anywhere else in Britain. Last frost is the usual planting signal, but tomatoes want warm nights rather than merely frost-free ones, and here those trail the last frost by weeks. Under cover you can plant about a fortnight after your last frost date. Outdoors, wait roughly six weeks.

Every date on this page is pegged to your region's real last frost rather than a UK calendar month, and no Scottish region ever resolves earlier than the UK-wide guidance. With a frost-tender crop an optimistic date does not cost you a smaller harvest, it costs you the plant.

Harden plants off before they go out, and plant deeply, with the first set of leaves just above the soil surface, so the buried stem roots along its length. Space plants 45cm to 60cm (18in–2ft) apart depending on eventual size. Irish growers work to a density of four plants per square metre, which is a useful way to plan a tunnel rather than a row.

In containers, allow one plant to a 30–45cm (12–18in) pot, or two to a standard growing bag. Cordons in pots get top-heavy, so put them against a sunny, sheltered wall. In the ground, work in plenty of garden compost first. Tomatoes want rich soil that drains freely but still holds moisture, and they should not go in the same bed two years running.

Watering

Water regularly and keep the soil or compost evenly moist. Evenly is the whole instruction. Tomatoes tolerate a great deal, but they do not tolerate swinging between bone-dry and soaked, and the two most common complaints about home-grown tomatoes both trace straight back to it.

Plants in containers dry out fast and may need water daily in hot weather. Curling leaves are an early warning that a plant is short.

Worth doing: sink a 15cm (6in) pot into the ground beside each plant and water into that. The water goes straight to the roots instead of sitting around the neck of the plant, where it encourages rot. That matters in a climate where the surface rarely dries out quickly.

Blossom end rot and splitting

A dark, sunken, leathery patch on the base of the fruit is blossom end rot, and it is probably the most misdiagnosed problem in tomato growing. It is worth understanding, because the fix is free and the popular fix usually is not.

The shortage is of calcium inside the fruit, which is not the same thing as a shortage of calcium in your soil. That distinction does most of the work here. In the majority of gardens the calcium is already present in plenty, and the plant simply cannot move it into the fruit quickly enough because the water supply keeps swinging between dry and drenched. Hot spells, very sandy or salty soil, and heavy nitrogen feeding all make that harder.

You will see eggshells, lime and calcium sprays recommended everywhere for this. Crushed eggshells certainly will not hurt anything, so by all means add them to the compost if you like the idea. Our honest view is that they are not solving the problem you have, because the calcium is rarely what is missing. It is your garden and your call, but before spending money on it we would fix the watering first and see whether the next truss comes good. In our experience it usually does.

Splitting and cracking come from the same root cause: the skin cannot keep pace with a sudden flood of water after a dry spell. Same fix, same habit.

Feeding

Start feeding once the first fruits begin to swell, not before. Early feeding buys leaf growth at the expense of fruit. Use an organic high-potassium liquid feed every 10 to 14 days for plants in pots and growing bags.

Tomatoes in well-enriched ground may need nothing extra, though a fortnightly feed will still lift the yield. They are hungry plants, and ground that had compost or well-rotted manure dug in before planting will carry them a long way. Mulch plants in the ground or in a greenhouse border with a thick layer of compost to hold moisture in, leaving a gap around the stem base so it does not sit wet and rot.

Pollination under cover

This is the step people skip in a Scottish greenhouse, and it costs them fruit. Tomato flowers need their pollen moved, and a closed tunnel on a cool, still day has neither insects nor wind to do it.

Open the vents regularly so pollinating insects can get in. On cold or still days, tap or gently shake each truss when the flowers are fully open, and mist the flowers with water. A truss that flowers and then drops without setting is usually a pollination failure rather than a feeding one.

Side-shoots, support and stopping

For cordon varieties this is the job that decides the crop. Left alone, a cordon throws out side-shoots from every joint between a leaf and the main stem, and turns into a sprawling mass that cannot be supported, takes up enormous space and carries very little fruit.

Every time you water, run your eye up the plant and pinch or snap out any shoot sprouting just above a leaf. Catch them at about 3cm and they come away between finger and thumb. Done weekly it takes seconds. Left for a month it becomes surgery. Bush varieties are the exact opposite: leave their side-shoots alone, and add a short cane where a laden stem starts to droop.

Support cordons with a tall, sturdy cane, or with a vertical string tied to the greenhouse roof and buried under the rootball at planting time, left slack enough to wind around the stem as it climbs. A stake wants to be about 1.2m. Tomatoes do not cling or twine, so every stem has to be tied in or wound on by hand.

Stopping means pinching out the growing point two leaves above the top truss, so the plant puts its remaining energy into ripening what it already carries. Do it when the plant reaches the top of its support, or once it has set seven trusses under glass or four outdoors.

Harvesting

Fruit starts ripening from mid-summer, though variety, fruit size and the weather all move that. Cherry types ripen fastest and beefsteaks slowest. Plants under cover start earlier and carry on well into autumn, which in Scotland can mean an extra month at each end of the season.

Check plants every few days and pick each tomato as soon as it is fully coloured, with the stalk still attached. Picking promptly keeps the plant productive.

The end of the Scottish season

Most Scottish growers end the season with unripe fruit on the plant. This is normal and it does not mean anything went wrong.

Do not leave them out hoping for a late warm spell. Lift whole outdoor plants and lay them on straw under a cloche to finish, or pick the fruit and put it somewhere warm and dark. A banana in the same drawer releases ethylene and speeds the whole lot along. Whatever stays stubbornly green makes very good chutney.

Problems to watch for

Given steady moisture and warmth, tomatoes are not a difficult crop. Four problems account for nearly everything that goes wrong here, and the first is in a class of its own.

• Tomato blight ends outdoor crops in a wet Scottish August. It is the same organism as potato blight. Growing under cover reduces the risk substantially, because the spores need hours of leaf wetness to take hold.
• Glasshouse whitefly is active all year round under cover, so a greenhouse gets no off-season from it.
• Grey mould (botrytis) thrives in the damp, still air of a closed tunnel. Ventilation is the main defence.
• Aphids very rarely kill a plant, and they feed a great deal of garden wildlife. Tolerance is usually the right response.

Blossom end rot, splitting and cracking are watering problems rather than pests. See above.

Common questions

Sources