Winter Protection for Your Raised Bed: Fleece, Film, or Nothing at All?

Every year in October, the same question comes up: do I need to cover my raised bed? With fleece? Film? Straw? Or just leave it alone?

The honest answer: it depends. But not on anything you don't know – it depends on three questions you can answer in two minutes.

🦔 Stachi here. Over the years I've tried every variation – unprotected winter bed, fleece tent, polytunnel, straw blanket. And I can tell you: the right system depends on what's currently in the bed. Not on what's on sale at the garden centre.

The three questions that decide everything

Question 1: What's growing in the bed?

This is the most important question of all. Depending on what's there, you need very different measures – or none at all.

• Empty bed (soil, maybe mulch): no winter protection needed. Lay mulch on top, done.
• Hardy plants (kale, winter purslane, lamb's lettuce, spinach): no protection needed down to -8 °C, fleece becomes worthwhile after that.
• Half-hardy plants (chard, Asian salad leaves): worth protecting from -4 °C, so fleece on cold nights.
• Tender plants you want to save over winter (young strawberry plants, herb pots): polytunnel or bring inside.
• Flower bulbs you've just planted: mulch is enough, no cover needed – they actually need the cold.

Question 2: What temperatures are coming your way?

In Switzerland and southern Germany: roughly speaking, elevations above 600 m get significantly more frost. In the lowlands – Zurich, Berne, Basel – winter minima typically fall between -5 and -12 °C on the coldest nights.

For fleece protection: P30 fleece (30 g/m²) protects down to about -5 to -7 °C. That's enough for lamb's lettuce and spinach on normal December nights at low altitude. For periods of persistent hard frost (below -8 °C for several days in a row), you can double the fleece or build a small tunnel.

Question 3: Do you want to harvest in winter, or are you just protecting?

This isn't a minor detail. Fleece keeps plants alive but makes harvesting awkward – you have to lift it every time, it mists up, and eventually it tears. If you just want protection, fleece is ideal. If you actively want to harvest, a polytunnel on steel hoops is the better solution: you can open it from the side, it lasts longer, and condensation drips off.

Fleece – the most widely used solution

Garden fleece, winter fleece, frost protection fleece – it's all the same thing. It's a thin, water-vapour-permeable polypropylene fabric that blocks frost while letting light and air through.

Pros:

• Cheap (roughly £2–3 per metre for P30)
• Light and rain pass through – no watering problem
• Plants can still breathe
• Quick to put up and take down

Cons:

• Doesn't hold up in very hard frost (below -8 °C) for long
• Tears if you keep pulling it up and down
• Slugs and mice can still get underneath

How to fix it down?

Clips, stones, soil anchors – all work. Important: fleece shouldn't lie directly on the leaves, otherwise the contact points freeze anyway. Either stretch it above the plants (with sticks or hoop frames) or lay it loosely with a bit of air space underneath.

Polytunnel – the more professional option

A polytunnel made of clear polyethylene film and metal hoops is more expensive (around £15–40 for a 120 cm bed), but far more durable and versatile.

When is it worth it?

• If you want to harvest over several months from behind your cover
• If you live at altitude or near mountain ranges
• If you want fresh salad leaves even in January

The problem with polytunnels: they store heat – far more than fleece. That's great against frost, but bad if the March sun suddenly shines on them and it hits 30 °C inside. You need to ventilate, regularly. Forget that, and you'll cook your winter salads.

Mulch – the often underestimated method

Mulch is not winter protection for plants growing above ground. But it does protect the soil and the roots.

What mulch actually does:

• Stops the soil from freezing too deep
• Retains soil moisture
• Protects plant roots (e.g. strawberries)
• Slows the freeze-thaw cycling that damages plants more than stable frost does

What mulch doesn't do: it doesn't protect leaves. A lamb's lettuce under 5 cm of straw would suffocate. Mulch goes beside or under plants – not on top of them.

Good mulching materials: straw (a bale from the farmers' market), dry leaves, dried grass clippings, shredded woody cuttings.

Doing nothing – when that's the best decision

With kale: covering it is counterproductive. Kale is so frost-hardy it actually needs sub-zero temperatures to convert starch to sugar and develop flavour. It's only really good after the first frost. No fleece, no protection – just leave it.

With lamb's lettuce and winter purslane: down to -5 °C they manage without help. In normal Swiss or Central European winter lowlands, that's usually not an issue until late November.

With an empty bed after the last harvest: add compost on top, add mulch on top, done. The soil does its winter regeneration, and that doesn't need a cover.

My tip for most raised beds

If you're not sure: buy 5 metres of P30 fleece (roughly £8–12). That's enough for a standard 120 × 80 cm raised bed. Then decide in November, once you see what's still in the bed and what the forecast says.

You only need a polytunnel if you actually intend to harvest through winter. Without that intention, it's not worth it.

And if your bed is empty: no fleece. Really. Let the soil breathe.

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🦔 Stachi here: Most of the money spent in the garden goes on things you never needed. Winter protection is, nine times out of ten, a piece of fleece – or nothing. Don't let the colourful autumn aisle at the garden centre throw you off. Ask yourself first: what's growing in the bed? The answer gives you your winter protection.

And if the bed is empty: lay some mulch on top, make a cup of tea, and wait for spring.

🦔 Stachi