Why a cloche earns its keep

A cloche is simply a portable microclimate, and in a British spring that is worth a great deal. Soil under glass or polythene in late February can sit several degrees warmer than the open ground beside it. Strawberry roots respond to that warmth by waking up sooner, pushing out fresh leaves earlier, and opening their first flowers a fortnight or more ahead of unprotected plants.

That head start matters for two reasons. First, the earliest trusses usually carry the largest and best-flavoured berries, so you are effectively buying yourself a longer picking season. Second, those early flowers are the ones most vulnerable to a late frost — and a single sharp night in May can blacken an entire truss before you have had a single strawberry from it. A cloche warms the soil and stands guard over the blossom. Few pieces of kit do double duty so well.

Choosing and siting your cloche

There is no single best design, only the one that suits your plot and your budget.

• Glass bell jars — the traditional look, heavy and elegant, ideal for a handful of specimen plants in a border or a large pot.
• Glass pane cloches — rectangular sections that run in a row along a planted line. Excellent light transmission, but they need careful handling and somewhere safe to live in winter.
• Polythene tunnel cloches — cheap, light and quick to move. Choose a wide, tall model so you can lift the cover and work underneath without dismantling the whole thing. Weight the edges down well; a March gale will send a light tunnel into the next county.
• Fleece over hoops — not rigid, but superb for throwing over on a frosty night and cheap enough to double up in layers.

Site your strawberries in full sun on free-draining ground. A gentle south-facing slope is ideal, because cold air drains away rather than pooling. Avoid the bottom of the plot, where frost settles like water in a bath, and avoid heavy clay that stays wet and cold into April. Raised beds and large pots warm up fastest of all and suit cloches beautifully.

Timing: from late winter to flowering

Set cloches in place from late February or early March, a good two to three weeks before you expect growth to start. If your plants are already in the ground, tidy them first — pull away dead and tatty leaves, clear weeds and any old straw, so you are not trapping damp debris underneath.

Plants under cover will need watering far more often than you expect, because rain cannot reach them and the soil dries quickly in spring sunshine. Check the top few centimetres with your finger and water at the base in the morning rather than splashing over the leaves in the evening.

As flowering begins, open the cloche during mild, still days so pollinating insects can get in. Strawberries are self-fertile, but they still need bees and hoverflies to move pollen between the flowers. A sealed cloche full of blossom may look productive and set almost nothing.

Varieties that repay early protection

Not every strawberry benefits equally. Early and mid-season cultivars put on the most growth under cover and give you fruit in late May or early June, well before the main flush.

• Gariguette — French, slim and intensely aromatic, a real treat when grown early.
• Honeoye — reliable, heavy cropping and one of the first to ripen.
• Cambridge Favourite — an old favourite with good flavour and steady yields.
• Elvira — vigorous and disease-tolerant, excellent for allotments.
• Royal Sovereign — admittedly fussier, but the flavour is superb when it crops well.

Late-season types such as Florence or Fenella gain little from cloching, so leave them uncovered and save the space. Perpetual or everbearing sorts like Albion appreciate a spell under cover in spring to get them moving, then crop on through summer and into autumn.

Ventilation, watering and grey mould

This is where most cloche growers come unstuck. On a bright April day, the temperature inside a closed tunnel can climb past 30°C, which stresses plants and creates exactly the humid, still conditions that grey mould (Botrytis) loves.

Vent every sunny day, opening ends and lifting sides in the morning and closing up again by mid-afternoon so warmth is retained overnight. On warm days, take the cover off entirely. Watch for the first sign of fuzzy grey growth on flowers or fruit, and remove affected material at once — do not leave it lying on the bed.

Other practical defences are worth the effort:

• Slip straw or a purpose-made mat under the trusses so berries never touch bare soil.
• Space plants generously and thin congested foliage to keep air moving.
• Feed with a high-potash tomato feed from first flowering, and go easy on nitrogen, which produces soft, mould-prone growth.
• Avoid overhead watering entirely once fruit has set.

Harvest and aftercare

With a cloche in place from early spring, expect your first ripe berries two to three weeks ahead of the neighbours. Pick in the cool of the morning, grasping the stalk just above the calyx so the fruit comes away clean and keeps longer in the fridge.

Do not whip the cover off the moment you start picking. Harden the plants gradually: open the cloche fully during the day for a week or so, then remove it once the risk of frost has passed in your area — usually late May in the south, early June further north. After that, net the bed against birds, keep the straw topped up, and peg down a few runners if you want new plants for next year.

Replace your strawberry plants every three years or so, starting a fresh bed from runners while the old one is still cropping. It keeps vigour high, disease low, and gives you another excuse to get the cloches out again next February.