7 Heritage Tomato Cultivars from Thompson and Morgan for Polytunnels

Brandywine, and why a 250-gram beefsteak struggles outdoors

Brandywine sets fruit in the 250 to 450 gram range, and that mass explains much of its poor showing in an open British bed. The plant needs a long warm spell to ripen a single beefsteak truss, while outdoor July and August rarely supply enough consecutive 20 degree days. Inside a polytunnel, with daytime temperatures five to eight degrees above ambient, Brandywine can finish a first truss by mid-August from an April sowing.

The Thompson & Morgan listing gives Brandywine at roughly 80 days from transplant to first ripe fruit, which is long by tomato standards. It needs an early start under a cold frame or in a heated propagator. A May direct sow leaves too little season for the crop to run properly. The plant is indeterminate and can reach 2 metres against the tunnel hoop, so a 2.5-metre internal height is useful. Its potato-leaf foliage is easy to recognise and, in humid cover, holds moisture longer than cut-leaf types. Spacing at 60 centimetres gives the leaves more air than a crowded 45-centimetre row.

Sungold and Gardener’s Delight in the same row

Sungold often carries a Brix reading between 9 and 11 in trial growers’ measurements, high for a commercial-bred F1 cherry. Gardener’s Delight, the older open-pollinated variety, usually sits around 6 to 8. Its sharper acid balance makes it better suited to cooking for some palates.

Both varieties are indeterminate, with long trusses and a strong place in the Thompson & Morgan cherry range. Sungold’s thin skin brings its main weakness. If watering becomes irregular after a dry spell, the fruit can split along the shoulder within hours. A polytunnel sharpens the problem because the grower controls every drop. A steady drip line or a fixed twice-daily watering routine matters more with Sungold than with a thicker-skinned type. Gardener’s Delight copes with the same neglect with much less cracking.

Gardener’s Delight has a Royal Horticultural Society Award of Garden Merit, a sign of reliable performance across varied UK conditions. It crops from roughly 60 days after transplant and keeps producing until the first frost stops the tunnel. One plant trained on a string support can throw 6 to 10 trusses through the season, with a dozen or more fruit on each. For a household eating tomatoes through September and October, two Sungold plants and two Gardener’s Delight plants usually cover most of the demand, with Sungold going straight to the table and Gardener’s Delight carrying the surplus into sauce.

Black Krim, where the dull skin is the point

Black Krim ripens to a dusky purple-brown shoulder that never looks fully done by supermarket standards. The colour comes from chlorophyll retained alongside lycopene, and it is part of the variety’s character. The flesh underneath is dense and low-acid, often described as smoky, with fruit running 200 to 300 grams in good tunnel conditions.

The variety originates from the Crimean Peninsula. Thompson & Morgan keeps it as an open-pollinated line, so seed saved from a ripe fruit comes true. Its weak point is structure. Black Krim cracks at the stem end under heat stress and bruises in handling; travel and storage are poor. Picked and eaten within two days is the realistic window.

Costoluto Fiorentino and the ribbed Italian habit

Costoluto Fiorentino arrives heavily ribbed, lobed like a small pumpkin, and the shape is exactly what Italian market gardeners selected over generations. The ridges give uneven slices and awkward packing, which explains its rarity in supermarket trays. The flesh is firm and acid-forward, built for reducing into a passata that keeps body.

The plant is a vigorous indeterminate and sets clusters that ripen unevenly across a single truss. Under cover, that habit can help the grower. The kitchen receives smaller pickings through late August and September, with less risk of a single-week glut. Thompson & Morgan lists it among the heritage Italian types, and packets usually run to around 10 seeds, reflecting the larger seed size of beefsteak-class tomatoes.

Dense foliage and deep ribbing trap humidity around Costoluto fruit. A still, warm tunnel in September gives Botrytis grey mould the conditions it needs on damaged fruit. Side-shoot removal, along with stripping lower leaves up to the first ripening truss, improves airflow around the crop. A roll-up side vent or a propped door does more for this ribbed variety than for the smooth-skinned cherries.

Cold frame to tunnel: the transplant schedule

Seed sown in February or early March in a heated propagator at 18 to 21 degrees germinates in 7 to 14 days. The seedlings then move to a cold frame for hardening before final planting in the tunnel.

That cold frame stage is where many heritage tomato losses occur. Overnight it can sit near frost risk, then climb past 30 degrees by midday if the lid stays shut under spring sun.

Prop the cold frame lid open by 10 centimetres on any morning above 10 degrees. Close it by late afternoon. Watch for damping-off, the fungal collapse at soil level that can wipe out a seedling tray in 48 hours.

A John Innes No. 1 or a peat-free seed compost, watered from below and kept just moist, reduces the risk. Once night minimums in the tunnel hold above 8 to 10 degrees, usually mid to late April under cover, hardened plants transplant with little check.

For one Brandywine plant on an 80-day clock, sow on 1 March, see germination by 12 March, pot on to 9-centimetre pots by late March, harden in the cold frame through the first three weeks of April, and transplant to the tunnel on 25 April. First ripe fruit should arrive around 14 July. Move the sowing to 1 April and the first fruit slides to mid-August. In a cooler season, that shift separates a full harvest from green-tomato chutney salvage in October.

Pollination under cover

A closed polytunnel keeps out the wind and most of the bumblebees that shake pollen loose outdoors. A daily tap on the flower trusses, or a roll-up side left open through the warm hours, moves enough pollen to set fruit. Without that movement, the first trusses on Brandywine and Black Krim drop their flowers.

Marmande, hybrids, and the blight problem

Marmande is a French heritage beefsteak, semi-determinate, with flattened ribbed fruit around 150 to 250 grams. It ripens earlier than Brandywine, often within 65 to 70 days of transplant. For a grower wanting a large heritage tomato without the long Brandywine wait, it is the practical choice, and Thompson & Morgan carries it in the continental heritage range.

Blight is the weakness running through every heritage variety here. Tomato and potato late blight is caused by the water mould Phytophthora infestans. It spreads on wet foliage in warm humid conditions, and a polytunnel’s biggest protective effect is keeping leaves dry. Heritage open-pollinated types lack engineered blight resistance. Modern hybrids such as the Crimson Crush and Mountain Magic lines were bred specifically for that trait.

Inside a well-ventilated tunnel, the dry-leaf advantage often outweighs the genetic vulnerability. In a humid, poorly vented tunnel, the same heritage plants are usually the first to suffer. A damp September exposes the gap between a catalogue description and the actual air movement under the cover.