At a glance
- Fleece works like a thin blanket: it holds back the warmth the soil radiates at night for a few extra degrees. Realistically that is two to five degrees, no miracle.
- Only lay the fleece on when frost is actually forecast, usually from CW 44 to 48. Plants kept covered permanently stay soft and grow more vulnerable.
- Air it out during the day: as soon as the sun comes out and it thaws, fold the fleece back. Otherwise moisture builds up and the plant sweats.
- Pots belong on wood or styrofoam, never directly on cold stone slabs. Otherwise frost draws up through the roots from below.
- A double layer of fleece plus jute holds back more cold than one thick sheet of foil. The air in between is the real insulation.
There is that one morning in late autumn when the lawn is white and your breath hangs in front of your face. If you still have salad in the bed or the olive tree on the terrace, it is time for the fleece. Frost is no drama here, just a matter of a few well-timed moves. Once you understand your fleece, you save yourself expensive plant losses and still do not have to check the weather app nervously every evening.
What fleece actually does
Garden fleece is a light, air-permeable textile made of synthetic fibre, usually with a weight between 17 and 50 grams per square metre. It conjures up no warmth of its own. What it can do is slow the radiation: on a clear night the soil loses its daytime warmth upward into the sky, and it is exactly this warmth that the fleece traps like a blanket. Two to five degrees of difference is the realistic range, a little more with several layers.
That sounds like little, but it often decides life or death for a plant. The difference between minus one and minus four degrees is precisely the threshold for a semi-hardy rosemary or the last autumn salads. Context matters: fleece works excellently against radiation frost on clear nights. Against an icy east wind at minus ten degrees over several days, a single layer does little, and that calls for heavier gear.
Frost is normal and part of the gardening year. Most native perennials and woody plants even need the cold. Fleece is only meant for the borderline cases: young sowings, semi-hardy herbs, Mediterranean potted plants and anything still to be harvested green.
Lay it on at frost, not in advance
The most common mistake is well meant: the fleece goes on in October and stays until March. That does more harm than good. Under permanently closed fleece the plant stays soft, keeps growing in mild weather and never hardens off properly. This soft new growth is then the first thing to freeze on the first sharp night.
Better is the open-hand principle: the fleece lies ready, cut to size and weighted down, but it only goes over the plant when the forecast announces clear nights with frost. In most locations that is the case from CW 44 to 48, roughly early to mid November. In wine-growing climates it can be later, in higher uplands earlier. Your own observation beats any calendar.
Remember the weather situation, not just the temperature. The dangerous nights are clear, still ones with a starry sky. Then the soil radiates its warmth unhindered and it gets markedly colder at ground level than the air temperature measured two metres up. Cloudy nights are almost always gentler on sensitive plants, even at similar readings.
Air it out by day, that is half the battle
Fleece is breathable, but it is no free pass. As soon as the morning sun climbs over the garden hedge and it thaws, fold the fleece back or take it off entirely. Two reasons speak for it. First, moisture otherwise builds up under the cover, and moist warmth is an invitation for grey mould and rot, especially among densely standing salads. Second, the plant needs the daylight, or it grows leggy under the cloth.
During continuous frost, when it stays below zero by day too, the fleece can stay on. But on every day with above-zero temperatures and sun the rule is: off. This small daily gesture makes the difference between a healthy plant in spring and a mushy little heap. If the on and off feels like too much, better not to cover at all and choose sturdier plants instead.
A fleece that is never aired out does more harm than the frost it is meant to protect against.
Old gardener's rule
The pot is the real cold trap
In the bed the plant has the advantage: the soil all around is a huge heat store, and frost only penetrates slowly. A pot, by contrast, is exposed to the air on all sides. The whole root ball can freeze through, and the roots are the most frost-sensitive part of nearly any plant. That is why many Mediterranean potted plants survive a winter in the pot worse than their planted-out relatives.
The most important measure is at the base: never stand the pot directly on cold stone slabs or concrete. From there the cold draws unchecked into the pot. A few wooden battens, a styrofoam board or dedicated pot feet create an insulating layer of air underneath. Wrap the pot itself in jute, bubble wrap or a coir mat, and on top comes the fleece over the crown if needed.
The four fronts on a winter pot
- Insulate from below
Wood, styrofoam or pot feet under the pot. This is the most important and most often forgotten step.
- Wrap the pot
Jute or bubble wrap around the pot wall so the root ball does not freeze through. Two layers with air between insulate better than one thick one.
- Protect the spot
Move it to a south-facing house wall or a wind-sheltered corner. The wall gives off residual warmth at night.
- Wrap the crown
Pack evergreen crowns loosely in fleece so they do not dry out in winter sun. Loose, not tight.
How to wrap a potted plant properly
Bring in or move it in time
Frost-sensitive species like olive, citrus or oleander move to a bright, cool, frost-free spot from CW 43 to 45. If you have none, push the pot against the sheltered south wall.
Stand it on a base
Two wooden battens, a styrofoam board or pot feet under the pot. Never straight onto the cold slab.
Wrap the pot wall
Wind jute, a coir mat or bubble wrap two layers around the pot and fix it loosely with coir twine.
Mulch the root zone
A hand's width of leaves, brushwood or bark mulch on the pot soil protects the upper roots as well.
Wrap the crown
For evergreens, lay the fleece loosely over the crown and tie it at the base of the pot. Leave enough air so the plant breathes.
Water sparingly, never into frost
Pots dry out in winter too. Water a little on frost-free days, but never right before a frosty night and never into frozen soil.
Never wrap dense plastic foil directly around the plant and knot it airtight. Condensation forms underneath, which freezes and damages the bark, and on mild days the plant practically cooks. Fleece and jute breathe, foil does not. If you use bubble wrap, then only around the pot for the roots, never over green leaves.
Olea europaea
- Familie
- Olive family
- Standort
- Full sun, in a pot against a sheltered south wall
- Saison
- Start overwintering from CW 43 to 45
- Wasserbedarf
- Low, only sparingly in winter
- Frosthärte
- Marginally hardy, to about -8 °C
Which fleece for which job
Not every fleece is the same. For frost protection what counts most is the weight. Thin fleece at 17 to 19 grams per square metre lets plenty of light through and suits light frost protection over vegetable beds that are still being harvested. Thicker winter-protection fleece at 50 grams per square metre holds back more cold but darkens more strongly, and it is more for pots and crowns that do not need to grow in winter.
A clever trick is layering: two thin layers with a finger's width of air between them insulate better than one thick layer, because the still air is the actual insulation. This is exactly why the combination of fleece plus jute plus a handful of leaves beats any single thick foil. And always weigh the edges down well with stones or ground anchors, or the first November storm carries your fleece off.
Buy fleece by the metre from the roll rather than ready-cut hoods. From the roll you fit it to every bed and pot, can layer it several times over, and pay considerably less per square metre. A fleece lasts several winters with careful storage.
What else in the bed wants protecting
It is not only pots that need attention. In the bed, fleece pays off for anything still green and to be harvested: lamb's lettuce, spinach, winter purslane, the last autumn salads and freshly planted garlic. Semi-hardy herbs like rosemary also thank you for a loose fleece hood on the sharpest nights, especially in rough locations.
Do not lay the fleece flat on the leaves, where it freezes and damages the tips, but stretch it over low wire hoops or tomato stakes into a little tunnel. That keeps a warming layer of air between cloth and plant, and to harvest you simply flip one side back. Root vegetables like carrots and parsnips are best left in the soil under a thick layer of leaves and lifted as needed.
Frequently asked questions
Frequently asked questions about frost protection with fleece
At what temperature should I lay fleece on?
As a rule of thumb: when frost below minus two degrees is forecast for the night and the sky stays clear, the fleece goes over sensitive plants. For semi-hardy herbs and pots, the first forecast frost is often enough. What matters is less the exact number than the weather situation: clear, still nights are more dangerous than cloudy ones at the same temperature.
Can the fleece stay on all winter?
Better not. Permanently covered plants stay soft, do not harden off and rot under trapped moisture. Only lay the fleece on when frost is forecast and air it out on mild, sunny days. Only during unbroken continuous frost may it stay on, since nothing thaws then anyway.
Why does the pot have to stand on wood or styrofoam?
Because otherwise the frost draws up through the cold stone slab straight into the root ball. The roots are the most sensitive part of the plant. An insulating layer of wood, styrofoam or pot feet breaks this cold bridge and keeps the ball several degrees warmer.
Fleece or bubble wrap, which is better?
Both have their place. Fleece is breathable and goes over green crowns and beds. Bubble wrap insulates more strongly but is airtight, so it belongs only around the pot wall, never over leaves. Over green foliage the foil would lead to condensation and rot.
Is one layer of fleece enough in hard frost?
In clear radiation frost, one layer gives two to five degrees. If it gets harsher or stays cold longer, layer up instead: two thin layers with air between them, plus jute and a covering of leaves at the base. The still air between the layers insulates more than one single thick layer.
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