Frost happens fast; fleece lets you sleep.
For most UK winters (zone 8a), use 30–35 gsm fleece for general protection, upgrade to 50 gsm in hard snaps or for containers, and keep 17–23 gsm for shoulder seasons and pest pressure. Cloches suit rows and mobility; cold frames suit trays and stability. Cover beds with pegged edges, leaf clearance, and vent on dry days so damp doesn’t beat cold.
What is horticultural fleece and which GSM do I need (UK)?
GSM: “grams per square metre” — a weight-per-area measure. Most garden fleece is spun‑bonded polypropylene with UV stabiliser; higher GSM = more warmth but less light and slower drying.
As a home grower in the East of England (zone 8a), I’ve tried the lot. The trade‑off is simple: the heavier the fleece, the warmer but dimmer and damper it gets. In our short‑day winters, plants need every photon they can get, so I keep 30–35 gsm as my default and only layer up when the forecast hints at a sharp snap or biting wind. Think of fleece as a small buffer (not a miracle heater) that takes the edge off radiative frost, especially over low, close-to-soil crops (salads, brassicas, herbs). Expect modest °C gains that vary with wind, wetness, and soil warmth. Venting matters more than people think.
If your’ve ever wondered why clear, still nights cause frost read this article from the Met Office>>
GSM cheat table (contextual, not absolute):
| GSM | Best use | Light transmission | Handling notes | Expected buffer* |
|---|---|---|---|---|
| 17–23 gsm | Autumn/spring covers; insect pressure; seedling hardening | ~85–90% | Very drapey; tears easier; dries fastest | ~0.5–1 °C |
| 30–35 gsm | General winter beds; low salads/brassicas | ~75–85% | Good balance of warmth vs light; anchors well | ~1–2 °C |
| 50 gsm | Hard snaps; windy/allotment sites; containers | ~60–70% | Heaviest; slower to dry; vent diligently | ~2–3 °C (single); ~3–4 °C (double) |
*Contextual buffer varies with wind, humidity, soil warmth, and sky clarity — use as a guide, not a promise.
Buying checklist: what “best” looks like (UK):
- GSM: 30–35 gsm UV‑stabilised, spun‑bond polypropylene for day‑to‑day winter use.
- Width: 1.5–2.0 m covers most 1.2 m beds with peg margin; wider for tunnels.
- Format: Continuous roll over pre‑cut sheets; fewer seams, easier anchoring.
- Tear resistance: Look for reinforced edges or be ready to hem with tape.
- Ventability: Light enough to lift daily; pair with low hoops on tall leaves.
- Storm plan: Keep a short 50 gsm roll for snaps/exposed sites; remove layer on next dry day.
Light vs warmth: when heavier hurts growth
In December–January, daylight is the limiting factor in the UK. Heavier 50 gsm can stall growth by cutting light and holding damp. Use 30–35 gsm as default, layer only for short snaps, and prioritise venting so leaves dry between cold spells.
Light loss, moisture retention, and °C buffer are the real trade‑offs; in dull Dec–Jan light, over‑spec’ing GSM can slow growth more than frost.
If you’re shifting to winter mulch and surface composting, our winter prep tasks post shows the 3–5 cm mulch top‑up that helps retain soil warmth under fleece → Prepare your garden for winter — 5 essential tasks (mulch top‑up).
For general frost prevention principles, see RHS winter protection guidance; we anchor our routine to the same fundamentals.
Choosing GSM is step one; how you house and vent that cover decides the outcome.
Cloche vs Cold Frame: which is better and when?
Cloches shine for row crops and quick moves; cold frames shine for trays, modules, and stability. Decide by wind exposure, access frequency, and light needs.
On my open allotment, low tunnel cloches handle wind better along rows and are fast to lift for a quick weed or harvest. At home, my cold frame (south‑facing wall) keeps module trays snug and is far easier to vent precisely without the fleece flapping. Frames lose a touch more light through glazing condensation but store more heat in still air. On bright, still days above ~6–8 °C, I crack both ends on cloches or open the frame lid a fist‑width to purge damp — it’s humidity, not just cold, that wrecks leaves in January.
Decision matrix (pick by context)
Cloches = rows, mobility, fast access. Cold frames = trays, stability, precise venting.
| Factor | Cloches (row tunnels) | Cold frames (lidded box) |
|---|---|---|
| Best for | Planted rows (salads, brassicas); quick moves | Trays/modules, hardening off, nursery area |
| Site exposure | Good on open beds if low, taut, well-pegged | Very good when sited against a wall/fence |
| Overnight warmth | Medium (air moves; add double fleece for snaps) | High (still air + mass; holds heat longer) |
| Light transmission | Higher (depends on fleece GSM) | Medium (glazing + condensation reduce light slightly) |
| Humidity control / venting | Ends lift; fast but coarse control | Hinged lid; precise gaps (finger-width to wide-open) |
| Access frequency | Very fast harvest/weed access | Slower (open/close lid), better for once-daily tasks |
| Wind handling | Good if rounded profile + pegs/bricks | Very good if sheltered; poor if freestanding & tall |
| Repairability | Easy (replace fleece/hoops) | Moderate (hinges, panes, seals) |
| Setup time | Minutes (hoops + fleece) | Hours first build; minutes thereafter |
| Mobility & storage | High (roll up, move between beds) | Low (fixed footprint) |
| Snow / rain load | Sheds if taut; shake snow | Lid can take some load; clear heavy snow |
| Wildlife/pests | Light deterrent only | Better against birds/foxes when latched |
| Cost | Low (fleece + pegs/hoops) | Medium–high (timber/polycarbonate + hardware) |
| When to prefer | Open allotments; frequent picking; rotating covers | Sheltered yards; seedling care; precise day-by-day venting |
Quick rules:
- Open, windy bed + row crops? Start with cloches (low profile, pegs every 50–60 cm, bricks on corners).
- South/East wall + trays? Use a cold frame (hinged lid = easy venting; site E–SE, shelter the north side).
- Hard snaps (≤ −3 °C) or exposed plots? Double fleece cloches or add 50 gsm inside the frame; remove a layer next dry day.
- Mid-winter growth focus? Prioritise light (30–35 gsm) and vent daily; humidity kills more leaves than cold.
Tip: If you can only buy one this year, get cloches + 30–35 gsm for flexibility; add a cold frame later for seedling precision.
In mid‑winter, venting discipline matters more than the structure; a well‑vented fleece tunnel beats a closed, sweaty frame for leaf health.
Practical notes on covers also appear in RHS crop covers guidance → RHS — Fleece & crop covers.
Ready to set a bed up the fast way? Here’s the 5‑minute method I rely on.
How to cover a bed with fleece (5 minutes)
Peg the long edges first, allow 2–3 cm leaf clearance, double fleece before hard frosts, and vent on dry days. Water in the morning only.
Venting schedule: Dry + sunny and >6–8 °C → vent 30–60 mins. Overcast/humid → brief midday vent. After hard frost → vent once leaves are dry.
Double‑fleece rule: ≤ −3 °C with wind/exposed beds or containers → add a second layer; remove next dry day to restore light.
Steps:
- Lay & size: Unroll fleece with the wind at your back. Leave 15–20 cm spare each side.
- Anchor edges: Peg the long edges every 50–60 cm; add bricks or timber on corners.
- Leaf clearance: Check leaves don’t press the fabric; add low hoops or twine over canes if needed.
- Double for snaps (optional): Add a second layer on forecast nights ≤ −3 °C; remove next dry day.
- Venting routine: On bright, dry days, lift ends or peel back a side to purge damp. Re‑secure before dusk.
Setup standards: Hoops 80–100 cm apart for low tunnels with a rounded profile to shed wind. Keep edges taut; re‑check pegs after gales.
–4 °C polytunnel night, 14 Jan — single 30–35 gsm over winter salad; uncovered leaves showed edge burn, covered leaves were harvestable next day. Result repeated two nights in that cold spell. On an open allotment bed, temps ran ~1–2 °C lower than a sheltered home bed; venting quality predicted leaf condition.
For the full winter plan across beds, trays and pots, see our Winter Gardening UK hub for tasks and timing → Full winter plan? See Winter Gardening UK for tasks & timing.
Beds sorted — now protect the weak spot most gardeners miss: roots in pots.
Protecting pots and containers from frost
Wrap pots with bubble‑wrap or hessian, lift them off paving, group by a wall for radiant warmth, and water only in the morning.
Roots are the winter failure point. In the ground, soil buffers cold; in pots, the root zone freezes fast and stays wet. I group containers tight against a south‑ or east‑facing wall, add pot feet or scrap batten to lift bases, and wrap the sides with bubble‑wrap held by twine — then drape fleece over the canopy on warning nights. Watch weight on large terracotta; sometimes it’s kinder to heel pots into a spare bed or compost bay for the worst weeks.
Quick checklist:
- Wrap sides (insulation), not just the top.
- Lift bases (drainage + frost gap) — no direct slab contact.
- Group tight by a wall; avoid wind funnels.
- Water mornings only; keep compost just moist.
Terracotta survival plan
If pots are large and exposed, heel them in to a spare bed or compost bay for 2–4 weeks of hard weather, or move them to a south‑/east‑facing wall. Keep compost just moist, never sodden.
Storm kit (contextual): Keep a short roll of 50 gsm fleece for the harshest nights on exposed plots → 50 gsm storm cover roll (Thompson & Morgan).
If you keep hens, icy troughs need a plan too — our Chicken Keeping in Winter guide covers water and ice routines that pair nicely with container checks → Keeping hens? Winter prep & water/ice routines for chickens.
Good covers last years if you treat them well — here’s how to make fleece pay for itself.
Care, reuse and storage (eco)
Dry before storage, fold loosely, patch small tears, and retire when light transmission collapses.
I hang fleece over a line or fence on the first dry day after a cold spell; moisture breeds mould and brittleness. Fold loosely (don’t crease hard at the same line each year), and store in a breathable bag — not sealed plastic. Patch tears with horticultural tape or off‑cuts using a simple overlap; if you can’t see the bed through it on a bright day, it’s time for a new piece. Expect 2–3 seasons from 30–35 gsm with good drying and shade storage; UV and abrasion are the limiting factors.
Plastic‑free options: Short‑spell covers can use wool‑based or paper/jute crop covers. They’re kinder on microplastics but insulate differently to spun‑bond PP — trial on a small bed first and still vent on dry days.
Sustainability tip: Buy one width larger than your beds so you can re‑hem rips and still cover comfortably next season.
With the hardware handled, what actually thrives under fleece in a UK winter?
What to grow under fleece in winter (UK, zone 8a)
Winter lettuces, lamb’s lettuce (corn salad), land cress, mizuna/mustards, and autumn‑sown broad beans all benefit. Plant early enough to size up before solstice; fleece holds that size through the coldest weeks.
In my beds, October‑sown lamb’s lettuce and land cress sail through under 30–35 gsm. Winter lettuces (’Winter Density’, ’Sarıkız’ types) hold leaves clean and pickable. Oriental mustards and mizuna stay tender with far less burn under fleece/tunnels. Autumn‑sown broad beans appreciate a layer on the harshest nights to spare the top growth. Sow/plant timing: late August–October for salads, September–November for broad beans (var. ’Aquadulce Claudia’).
Onions and garlic planted in Autumn do not need to be covered by fleece. The Frost helps improve the flavour of garlic.
Picking hardy varieties? Our frost‑resistant plants list helps you choose crops that shrug off cold under fleece → See our top frost‑resistant plants for UK gardens.
Even good crops fail if we smother them — avoid these common traps.
Common fleece mistakes & fast fixes
Over‑watering, smothering foliage, never venting, and poor anchoring cause most winter failures.
- Damp beats cold: If leaves feel clammy at noon, vent. Prioritise drying the canopy over hoarding heat.
- Leaf contact: Fleece touching leaves wicks frost — add a hoop or twine ridge.
- Watering: Morning only; dry foliage by dusk. In Dec–Jan, many beds need less than you think.
- Snow load: Shake off heavy snow so fabric doesn’t press leaves; in prolonged wet, vent between showers to dry the canopy.
More ways to safeguard? Our Winter plant protection guide pulls fleece, cloches and mulch into one plan → Winter plant protection — how to safeguard your garden from frost.
Quick answers below if you’re skim‑reading for a specific problem.
FAQs: Horticultural Fleece UK
What GSM fleece for winter in the UK? 30–35 gsm suits most UK beds through winter; add 50 gsm for hard snaps or exposed/allotment sites and for container wraps. Keep 17–23 gsm for autumn/spring and for light‑hungry tasks like seedling hardening.
Can I double fleece plants? Yes — double for short, sharp snaps (e.g., forecast ≤ −3 °C), then remove a layer on the next dry day to restore light and airflow. Always vent to prevent botrytis.
Do I leave fleece on during the day? Usually yes in Dec–Jan, but vent on dry, bright days. If temps rise above ~6–8 °C with sun, peel back ends or one side to purge damp and avoid scorch on evergreen leaves.
Cloche vs cold frame — which keeps plants warmer? Frames generally hold heat longer overnight, especially against a wall. Cloches are more mobile and can be double‑fleeced. Either way, venting discipline matters most for leaf health.
How do I stop fleece blowing away? Peg the long edges every 50–60 cm, add bricks on corners, and avoid slack. On very exposed plots, use low hoops to keep a rounded profile that sheds wind.
How long does horticultural fleece last? With good care (drying before storage, shade storage, gentle handling), expect 2–3 seasons from 30–35 gsm. UV and abrasion are the limiting factors.
Can fleece touch leaves? Try not to — contact can wick frost onto leaves. Add a low hoop or twine ridge for clearance.
Should I remove fleece if it snows? Shake off heavy snow so the fabric doesn’t sag onto foliage; re‑secure. Vent between showers in prolonged wet to prevent botrytis.
What can I use instead of horticultural fleece? Planned alternatives: cloches (polycarbonate tunnels or bell cloches) and cold frames for stable, ventable cover. For containers, use bubble‑wrap or hessian wraps and group by a warm wall. Emergency options: old sheets/blankets overnight (remove next morning), or a cardboard box over small plants. Mulch (straw/leaves) protects roots, not leaves — combine with a cover on frost nights.
Does horticultural fleece let rain through? Yes — it’s permeable to air and water. Heavier GSM slows penetration; water may bead then pass through. Still vent between wet spells to dry leaves and avoid botrytis.
Does garden fleece protect plants from frost? It reduces radiative heat loss and wind‑chill, giving a small but meaningful buffer (see GSM table). It’s most effective on clear, still nights and when leaves are dry.
Does horticultural fleece work? Yes — when anchored, vented and sized correctly. In our tests (–4 °C polytunnel night), covered winter salads remained harvestable while uncovered leaves scorched.
What is the best horticultural fleece in the UK? For beds, choose UV‑stabilised 30–35 gsm spun‑bond PP on a continuous roll (1.5–2 m wide). Keep 50 gsm for short, harsh snaps or exposed/allotment sites.
Where to buy horticultural fleece UK? Garden centres, online garden retailers (e.g., Thompson & Morgan), and DIY/general retailers (e.g., Screwfix, Amazon, B&M). Check the GSM, width, and UV rating before you buy.
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