How Do I Use Horticultural Fleece to Protect Plants from Frost?

Horticultural fleece is one of the most versatile and affordable frost protection tools a kitchen gardener can own. A roll of 17 gsm fleece costs very little and can be the difference between a thriving early crop and a blackened disaster after a late spring cold snap.

What Horticultural Fleece Does

Fleece is a spunbonded polypropylene fabric that creates a still-air layer around plants. That trapped air acts as insulation, typically keeping temperatures 2–4 °C higher under the fleece than outside. Light, water, and some air still pass through, so plants can photosynthesize and breathe while protected. It also buffers against wind chill, which dramatically increases the damage rate of cold air moving across exposed foliage.

Choosing the Right Weight

Fleece is sold by weight in grams per square metre (gsm). Lightweight 17 gsm fleece lets through good light levels — suitable for everyday season extension and light frosts. Medium 30 gsm fleece provides stronger frost protection (up to 5 °C gain) but transmits slightly less light. Heavy 50 gsm fleece gives maximum frost protection but is opaque enough to slow growth if left on for more than a day or two. For most gardens, 17–30 gsm is the practical range: deploy heavier grades only when hard frost is forecast.

How to Apply Fleece Correctly

Lay fleece loosely over plants, leaving slack so foliage is not pressed against the material — contact with cold fleece can cause localised frost burn. Weigh or peg edges securely so wind cannot lift it. For rows of low crops like lettuce or spinach, simply drape it over the row and tuck edges under soil or weigh down with canes. For taller crops like young tomato transplants, support the fleece with hoops or a simple wire frame so it forms a tent rather than lying on the plants.

Apply fleece before the frost arrives, ideally in late afternoon, to trap the day's warmth inside. Removing it in the morning once temperatures rise above freezing prevents the trapped heat from scalding plants on a sunny day.

Can Fleece Stay on All the Time?

Short-term continuous use (a week or two) is fine for cold, overcast weather. During active growth in spring, remove fleece during the day if temperatures are above 5 °C to allow good light, ventilation, and pollinator access for flowering crops. Leaving fleece on permanently in mild, bright weather encourages drawn, weak growth and can create fungal humidity. Use it as a protective blanket at night and during cold spells, not as a permanent cover.

Storing and Reusing Fleece

Good quality fleece lasts three to five seasons if handled carefully. Shake out soil and debris before storing, roll loosely, and keep dry. Avoid folding sharply along the same lines, as this weakens the fabric. Cheaper single-use fleece degrades quickly in UV light, so cover it with a tarpaulin if leaving it on over weeks.