Cover materials, laid simply and quickly over plants, give you options for extra and more successful plantings. There are two main types:
- Lightweight fleece covers – these are a quick and easy way to increase your harvests and to enjoy them earlier. Use them mostly in early spring.
- Stronger mesh covers – these give excellent protection against pests, as well as mitigating weather extremes. You can use them at any time of year.
Fleece is a thin, unwoven, polypropylene fabric. It is more like cloth than plastic – soft, light in weight and flexible – and comes in varied thicknesses, most commonly from 17 to 30 gsm in horticulture. The thicker material, of 30 gsm (close to 1 oz / yard), lasts for several years of use. The 17 gsm grade often splits after a few weeks and is best avoided.
Mesh, by contrast, is a woven, nylon fabric which is slightly thicker, heavier and stronger than fleece. It can give 10 to 15 years of use, before possibly having too many holes to be used against insects, though it could still serve to protect plants from animals and birds.
Lay flat, or on hoops?
How you use these covers depends partly on likely wind strength, because when covers are on hoops wind can get underneath a little, which then agitates and damages them. Even the thicker grade of 30 gsm fleece may be damaged by high winds, and the wind is stronger above ground level.
For most plants and in most weather, it’s feasible to use covers at ground level, directly sitting on leaves. This especially applies to fleece, because it is so light in weight.
- A bonus of this easy approach is that warmth is held closer to plant leaves and the soil.
Vegetables mostly thrive when fleece lies directly on top of them. It can be fairly tight, which is kinder to leaves than having it loose and flapping in high wind. Even the fine and tender-looking leaves of onions can push up a fleece cover – their leaf tips curl downward under the cover’s light weight but then straighten quickly once it is removed.
The main possible damage is to tips and edges of leaves that come into contact with freezing fleece in frosty weather. The damage can look bad, but plants usually recover. However, if April frosts are hard and frequent, consider using battens along a bed, to lift fleece slightly above ground level, as in the photo, below right.
Using hoops
Covers can be supported with hoops, spaced at 1–1.5m / 3.3–5ft. Potential damage from wind is less likely in frosty weather, when it’s usually not windy.
My favourite hoops are made of 4 mm / 0.2 in galvanised, high-tensile wire. You need to buy this in pre-cut lengths, rather than buying a coil and cutting yourself, because the wire is impossible to straighten by hand and needs to be machine-straightened after cutting.
The wire retains its straightness, which makes it easy to store in a space-saving way. Then you can easily bend it to any shape, according to the width of your bed and the height of cover you require. The best wire length to span over a bed of 1.2 m / 4 ft width is 2.5 m / 8.2 ft.
Securing edges
Wind can be the main issue when using covers. Fortunately, they are not difficult to hold in place because of the way that the wind blows through them. At Homeacres we use stones or rocks of medium weight, placed at every metre along the sides. Don’t use soil because it’s then difficult to access plants underneath, and the covers become dirty.
Before putting stones in place along the sides, place a heavy rock on each end of the cover, in the middle of beds (see photo below). This tensions the cover lengthwise and makes it less likely to blow and tear in wind.
Sunshine and watering
The heat of sunshine is potentially a concernafter about mid-April, and especially after dry weather when plants’ roots may be struggling to find moisture. Check the weather forecast and you can then remove fleece before a hot day, or give extra water in the morning through the fleece, and leave it on.
It works to apply water through fleece and mesh. It’s only covers of fleece being used for the first time that may be a little oily and shed some water. It works well not to use a rose on the watering can, because fleece itself breaks the force of water. Plus water passes through more effectively when it’s a reasonably full flow, rather than fine droplets.
Use repeatedly, store between
Dirt is not a problem for either fleece or mesh. You should never need to wash covers because rain does a good job and, importantly, there isn’t much mud in a no dig garden. I notice that on farms and allotments where soil is tilled and dug, the covers become brown which excludes some light.
The best way to store covers after use is by looping them above head height, over, say, a batten in your shed. Then they are not available for mice to nest in over winter, which would result in many holes.
Plastic or natural fibres?
Concerns about microplastics do make me wonder about the use of fleece covers, which is frustrating because they work so well.
All I can say for now is that I hope not to buy any more, and in 2020 I purchased cotton muslin to trial. It was expensive, £55 / approx. $75 for 1.5 x 20 m / 5 x 66 ft, and needs to serve for many seasons in order to be cost-efficient.
Muslin gives weather protection, but has some differences in comparison to fleece:
- It degrades into holes along the sides, underneath the stones holding it in place.
- Growth under muslin is slower than under fleece. The cotton retains a little less warmth, and is slightly heavier on plants if not supported by hoops, especially when wet.
For the time being I will continue to use the fleece covers I have, while also trialling the muslin.
Other covers and extra securing against wind
Another type of cover is Thermacrop, a hybrid between fleece and mesh. It’s stronger than fleece and has wider holes than mesh, which means that small insects can pass through. It’s also heavier than both of the other types and works well in winter to protect plants, supported on hoops. However, it’s then at risk of being lifted by the wind.
We have a nice method for preventing this, for which you need a number of extra hoops of the same length. Once a cover is in place on top of hoops, you can then add more hoops on top of the cover, at every third under-cover hoop (see photo below left). With wire hoops, this is quick and easy.
One more type of cover we use is netting, with 12 mm / 0.5 in squares. It’s made of UV treated polypropylene and lasts for many years, and is used mainly to prevent larger animals and birds from eating plants.
Seasonal use of covers
Vary the covers you use according to the season, the weather, and likely pests in relation to which vegetable you are growing. This may sound complicated, but here are a few common-sense guidelines to guide you through those choices.
Using fleece covers in the spring
I use fleece mostly in the spring, when the weather is cold but the days are long and the sun is strong. This is shown in the photos, below, of snow melt in March 2018. Although not much is growing in the garden, the sun has warmth and snow melts rapidly.
- The sunlight at spring equinox is as strong as at the autumn equinox, but the temperature is far lower.
- Fleece covers equalise this imbalance by converting light to warmth. Without them, much of the bright light in spring cannot be used by plants, because it’s too cold for them to grow.
Warmth increases under fleece covers even when there is no bright sunlight. Cloudy days in spring time have sufficient light to convert into warmth below a cover. In addition, plants are protected from wind and any heavy precipitation.
Using fleece covers brings planting dates forward by two to three weeks, to ensure earlier harvests through late spring and early summer, as well as earlier second plantings for better harvests in autumn and winter. The net increase of growth is considerable.
A further benefit is having fewer plant losses due to pests, such as rabbits and pigeons.
Other difficult pests that you need to be aware of are slugs, in particular if it rains a lot in the two to four weeks after sowing or transplanting. You can roll back any cover at dusk, to check for and remove any slugs, before re-covering.
It’s at least encouraging that after year one in a no dig garden, it’s rare to suffer much slug damage. Just be sure to keep beds and paths clear of weeds, maintain tidy edges around the growing area, and use compost as your main mulch. If any of your beds have sides with decaying wood, these will be harbouring slugs and it’s best to remove or replace them.
Fleece covers give you peace of mind that plants are likely to survive, from being protected in adverse weather, and from not being eaten.
At Homeacres I use covers on every early planting, and from late March and through April the garden is white, with either fleece or frost! Seedlings grow slowly but surely – all plantings at this time are of frost-hardy plants, including peas, lettuce, onions, brassicas and coriander.
As spring progresses, frosts become less likely and are less severe, with the wind lightening, one hopes. On the other hand, by mid-spring there are frost-sensitive leaves, such as early potatoes.
Keep alert to the spring weather forecasts for mention of any frost, in which case:
- Lay fleece or extra fleece over potato plants on the evening before a freezing night, to reduce any damage. You can cover with two pieces of fleece if the frost looks to be strong.
- Drape small pieces of fleece on top of seedlings in your propagation area, where freezing in April and May can be catastrophic for tomatoes, courgettes, sweetcorn, cucurbits, basil and others. It’s better to be safe than sorry.
HOW LONG TO LEAVE COVERS ON
In early spring, the average time for new plantings being covered is around four to five weeks. Except in a rare heatwave, with afternoon temperatures above 21°C / 70°F, you can leave covers on 24 hours a day, including in bright sunshine (as explained above).
Keep a watch for weeds growing – you can then quickly and temporarily roll back covers to remove them when they are still small.
At Homeacres, the time of maximum benefit from fleece covers is from early March to 20th April. However, in a cold spring the covers remain beneficial and stay in place until early May.
April 2018, for example, was colder than usual, and we removed the covers on 3rd May. Growth was then meteoric, thanks to fleece having enabled the growth of a strong root system.
RESULTS IN SUMMER, FROM COVERING IN SPRING
The three photos directly below are all from 2019, and show how much a vegetable garden can grow and change in just a few months.
Spring covers help to make this possible, by elongating the growing season and creating time for second plantings to grow to a decent size.
Fleece in a cold summer
In the summer of 2012, we suffered a lot of rain, cloud and cool days (16°C / 60°F) through June and July. In this exceptional weather, the fleece cover that I kept over courgette plants until 24th June made a big difference (photos below). It helped them to grow through the adverse conditions.
Thankfully it’s rare that fleece is necessary or effective after spring finishes, even on frost-tender plants. You should be fine to remove fleece from new plantings of courgettes by early June, and sometimes may not need to use it at all, as long as the weather is kind in late May.
Covers in autumn
Autumn covers are mostly about pest protection, such as for rabbit-vulnerable plants like endives, and pigeon-fancied plants such as salad rocket. At this time, I advise using mesh covers, for their extra strength against weather, and because mesh admits a little more light than fleece.
Mostly it’s not effective to use fleece in autumn, because there is often sufficient warmth coupled with the relative shortage of light. In other words, the opposite of spring.
By early October, light levels are the same as in early March. Covers reduce the light reaching plants, which is absolutely not a problem during the bright days of spring, but can be in the autumn.
However, when an early frost is forecast, it’s worth using fleece to cover sensitive plants such as Florence fennel and celery, and even beans if they are still cropping.
Covers in winter
In a temperate climate such as here, the main value of winter covers is wind protection, in particular for tender new plantings. Pest protection can be important too, especially on brassica plants against pigeons.
For tender plantings made in autumn, growth in winter is stronger when under a cover held up by a low cloche, to reduce wind damage from flapping on leaves. However the cover may blow off in a gale, and it can be better to lay it directly on top of plants so that wind is less likely to lift and rip it. Whether or not you choose to support covers through winter depends mainly on your climate.
Covers against pests
When using covers against likely pests, they need to be in place a good week or two before the pests normally arrive. If unsure of any dates like this, best consult local knowledge.
In particular, it’s highly worthwhile to cover all new summer transplants of brassicas with mesh, before pests such as butterflies, flea beetles and gall midges can damage plants. For flea beetle and aphid protection, you need the finest grade of mesh cover. For most other pests, a standard grade of mesh gives sufficient protection.
Covers applied too late can make problems worse, and can even protect pests that are already on the plants, by denying access to predators such as wasps.
In 2019, I laid mesh over winter carrots on 4th September, three weeks too late. They had been sown on 19th June, between lettuce that were being harvested weekly. I knew it was probably too late, but felt it was better to try at least. The reason for the delay was that I had been waiting for a chosen few seeding lettuce plants to become harvestable, which didn’t happen until early September – I had hoped they would be ready earlier.
We got the lettuce seed, but lost many carrots to damage from maggots of root flies (see photo below). Cover summer-sown carrots against root fly by early to mid-August.
Options for pest protection
Fleece is more likely than mesh to develop holes. One summer I tried to protect brassicas against butterflies, using old fleece. There was a hole that I had not seen and butterflies flew in, resulting in leaf damage which was far more extensive than where I had used no cover at all.
The uncovered plants were free to wasps and birds, who ate some insects.
- For spring protection against cold, as opposed to keeping insects out, you can use old fleece with some holes.
- For summer protection against insects, use a mesh cover immediately after planting, for up to two months.
You can also spray Bacillus thuringiensis on plants that are prone to damage from caterpillars, such as all brassicas. Here we use it every 18–20 days, from mid-July to September.
