Using garden bed covers like mini hoop tunnels, row covers, or portable cold frames is my secret to a bountiful and healthy vegetable garden. These versatile covers allow me to increase production, reduce pest and weather damage, and extend the harvest season into fall and winter. In my book, Growing Under Cover, I write about the many ways both small and large covers can be used in a home vegetable garden. Read on if you want to learn more about using protective covers in your garden.
6 reasons to use garden bed covers
There are many benefits to growing under cover. For me, the main reason is that covers allow me to create a microclimate around my plants, capturing heat and increasing production. Here are other benefits to using garden covers:
- Protect from frost – Frost protection was my initial goal when I began using garden covers and I still use them to shelter vegetables from a sudden dip in temperature. Frost covers, like row covers, polyethylene sheeting, and cloches are mainly used in spring and fall.
- Protect from bad weather and control the environment – While I use covers to prevent frost damage, I also use them for other types of extreme weather like hail, downpours, and strong winds. Covers for bad weather are generally temporary and used just for a few hours or perhaps a day or two. For example, a metal or plastic bucket overtop a newly planted tomato seedling offers effective temporary protection from inclement weather. Or you can set up a quick mini hoop tunnel over a raised bed to shield vegetables from sudden storms.
- Reduce pest damage – Garden covers can protect from insect pests like flea beetles and cabbage worms, but also larger pests like deer and rabbits. Unlike those used for temporary frost protection, covers for pest prevention are typically left in place for weeks or months and must therefore allow light to pass through. Insect netting and barrier fabrics are perfect for the job.
- Enjoy a year-round crop – A garden bed cover like a mini hoop tunnel or cold frame can protect from temporary bad weather like frost or hail, or you can use them to stretch the harvest season into autumn or even winter. It’s not just about winter harvesting however as many covers and structures give you a jump on the spring planting season so you can harvest months earlier.
- Save money – Using garden covers to maximize production helps me grow more food and save money. Plus, I get to enjoy a hyperlocal harvest and reduce the need to buy greens and vegetables trucked in from far away.
- It’s easy! Yup, it’s easy to be an undercover gardener. I keep row covers, shadecloth, and polyethylene sheets folded and stacked in my garden shed. Wire, metal, and PVC hoops are lined up outside the shed. If the weather take a sudden downward turn, it only takes me a couple of minutes to set up a few hoops and cover them with a length of row cover.
Types of garden bed covers
There are many types of garden bed covers you can use in your food garden. When I first began to extend my season almost two decades ago, I started with row cover, a fabric-like material easily sourced from garden centres. Since then, I’ve experimented with many types of garden covers in both in-ground and raised bed gardens including portable cold frames, shade cloth, mini hoop tunnels, and an unheated polytunnel. Below is a list of some of the more common types of garden covers.
Also known as reemay, these are lightweight, fabric-like covers often used for frost protection. They come in a variety of weights and sizes and can be cut to fit your garden space. There are three main types of row covers: lightweight, medium-weight, and heavy-weight. Keep in mind that the heavier weight fabrics only allow 30 to 50% of light to pass through and are meant for temporary or winter protection. I generally use lightweight row covers (which allow 85 to 90% of light to pass through) as longer-term garden bed covers.
Insect barrier fabrics, netting, and meshes
These materials are usually floated on hoops over a bed to omit insects or other pests from accessing your crops. I use bird netting or chicken wire on top of hoops to prevent deer or rabbit damage. They can also be used to keep cats, dogs, and chickens out of beds. For insect pests like squash bugs or cabbage worms, you can buy insect netting or translucent insect barrier fabrics that allow water, air, and 95% of light to pass through to your plants but block insect pests.
There are various grades of plastic sheeting you can buy to use as garden covers. Construction grade films, like those used as drop cloths when you’re painting are very thin and tear easily. They also don’t offer much protection against frost or cold weather. I prefer 6 mil greenhouse plastic which is sold in pre-cut sizes, by the running foot from select garden centres, or by the roll. I usually buy a roll and cut it into the sizes I want. It saves money and I can always split the cost with gardening friends. Greenhouse plastic is also UV treated and doesn’t break down quickly in the sun like cheaper plastic sheeting.
Shade cloth is an underappreciated cover that has a place in both southern and northern gardens. I use lengths of shade cloth when the weather heats up in late spring to delay bolting of salad crops like lettuce, arugula, and spinach. I also use it in summer over beds that have been newly seeded or transplanted with successive crops. The temporary shade keeps the soil from drying out too quickly which boosts germination rates and reduces transplant shock. In warm climates, a length of shade cloth can be hung over an entire garden or greenhouse to reduce temperatures and minimize heat damage to plants.
Mini hoop tunnels
While garden covers like row covers or insect barrier fabrics can be laid directly on top of crops, I prefer to float them on hoops. It looks tidier and it’s easier to vent and care for the crops beneath. Depending on the season, the reason for the cover, and whether it’s temporary or long term I use different materials for the hoops. For a quick, short term tunnel, 9 gauge wire can be cut and bent into U-shapes and inserted into raised or in-ground beds. For sturdier hoops, I use half-inch diameter PVC or metal conduit. To bend metal conduit, you’ll need a metal hoop bender. Metal hoops are very strong and I rely on them for my winter tunnels. They stand up to a heavy snow load far better than PVC or wire hoops. Read more about bending metal hoops here.
Cold frames (portable and permanent)
Cold frames can be DIY’d or purchased online or in garden centres. I’ve used many types of cold frames over the years and found all have their place. Permanent frames made from wood and topped with a sheet of polycarbonate or an old window are sturdy structures. I’ve placed them on top of a garden bed or sunk them down into the soil to boost heat retention. If you live in a cold climate and wish to winter harvest, stick to wooden-sided frames. For lighter protection – spring and autumn seed starting or harvesting – you can use a polycarbonate cold frame where the sides and top are made from 4 mm thick polycarbonate. I consider these portable frames and often move them around my garden placing them on top of crops like lettuce, carrots, and kale.
Cloches are a temporary garden bed cover but one that can be effective in spring and fall. Traditionally, cloches were bell-shaped glass jars that were placed over plants to protect them from cold weather. And while you can still buy these stylish cloches for your garden, they’re more decorative than practical as they’re expensive and breakable. Instead, I like to upcycle milk and water jugs, juice containers, and other items to use for cloches. I place them overtop newly transplanted pepper and tomato seedlings in spring, removing the cap to prevent heat build-up. Packs of plastic cloches are also available online and in garden centres. Cloches do a fine job of protecting a few plants but if you have a lot of seedlings or entire beds to cover, I’d suggestion a mini hoop tunnel instead.
How to use garden bed covers effectively
Using covers like plastic sheeting and shade cloth is pretty straightforward, but I’ve got a few tips to help you get the most out of your garden covers:
- Vent – This is the most important task to remember when using garden covers like mini hoop tunnels, cold frames, and greenhouses. It’s amazing how quickly the temperature can climb beneath a cover, even on an overcast day. For example, it may be just 40 F (4 C) outdoors in early spring but if the sun is out the temperature inside a mini hoop tunnel can quickly climb to 68 F (20 C). You can use an indoor/outdoor thermometer to keep an eye on the temperature or just plan to open the ends of mini hoop tunnels and the tops of cold frames when the temperature is a few degrees above freezing.
- Water – Certain covers, like row covers and shade cloth are porous and allow water to pass through. Others, like plastic sheeting are not and you’ll need to keep an eye on soil moisture if they’re left in place for more than a few days. I’m often asked about winter watering. I don’t irrigate in winter when plants are tucked beneath their protective covers as the soil is frozen and the frigid weather reduces transpiration.
- Secure covers well. It goes without saying that once you have covers over your beds you want them to stay in place. Strong winds, winter weather, or even pests can knock covers off. I use snap clamps to hold row covers, shade cloth, and plastic sheeting to hoops, but you can also weigh the sides of the cover down with rocks, logs, and other heavy materials.
- Watch for pests. A cozy cold frame or greenhouse bed may prove tempting to a family of mice in late autumn as outdoor temperatures plummet. If you’ve had rodent problems before, it’s helpful to install metal mesh hardware cloth at the bottom and sides of a cold frame when you build to prevent mice from entering the structure.