All About Cloches

Gardeners are always trying to extend boundaries by squeezing in just one more tomato plant, or planting a shrub that should grow in a warmer climate zone. And we'd all like to find a way to stave off Jack Frost for a while before he ends our gardening season. You can improve the odds and extend the frost-free date: simply cover plants to retain heat and keep out cold.

Cold frames, greenhouses, and hoop houses are great protectors against the elements, but these semipermanent structures are not easily portable. For long rows of lettuce or greens, plastic row covers or floating row covers offer sufficient protection. If you have only a few tender basil plants or a prized hot pepper, you can simply throw a blanket over them, but a more effective way to keep them growing is to cover them with an individual plant protector, often called a cloche.

Cloches Up Close

Cloche (pronounced kl-osh) is the French word for "bell." The original cloches were large bell-shaped jars that 19th-century French market gardeners placed over plants in spring and fall to act as portable miniature greenhouses. At one time, these glass jars covered acres of fields outside Paris that supplied out-of-season vegetables to the city's households and restaurants. European gardeners also used barn-shaped glass cloches such as my favorite, the Chase cloche. These once popular cloches were constructed of panes of glass held together by cleverly crafted wires. They could be attached end to end to form a tunnel and cover rows of plants. Unfortunately, the glass barn cloches are no longer available, but home gardeners can use less elegant plastic row covers to fulfill the same function.

The classic glass bell jars are still available but have some significant limitations. Because they are made from heavy glass and are small, the air trapped within can quickly get too hot on sunny days and possibly kill plants. Pay close attention to ventilation. A professional gardening friend, trained in France, tells of trudging out to cloche-covered fields on bright, frosty mornings to slide a block of wood under one side of each cloche to vent it during sunny days. He'd return in late afternoon to kick out the blocks, so the cloches would sit flat on the ground and seal in the warm air for the night.

Although modern versions of these individual cloches are not as elegant as the traditional glass bell jars, some offer the same or a better degree of frost protection, are made of lightweight materials, and are easier to vent. Some are also convenient to store. Types of cloches range from those you can make from plastic milk jugs to elegant lantern cloches:

  • Solar umbrellas fold and unfold for easy storage. The spike handle holds the umbrella in place, and its height can be adjusted for venting.
  • The lantern cloche is made of an aluminum frame and double-walled, rigid plastic for optimum durability. The pyramidal top can be set ajar for venting.
  • A plastic version of the traditional glass jar cloche, the solar bell is lightweight, durable, and inexpensive.
  • Utilitarian plastic milk jugs with the bottoms cut out are vented by opening the lid. However, they offer only a few degrees of frost protection.
  • The plastic grow dome is sold as two halves that snap together. It's easily vented by snapping open the holes on the top.
  • The tomato plant cover has a clear plastic top that snaps on for frost protection and can be removed for venting. It needs support in high winds.

Cloche Considerations

In my garden, I use cloches in many ways. Obviously, they provide great protection for any newly planted seedlings, but they also protect mature plants in fall. My bell-shaped glass cloche offers winter protection to my one sea kale (Crambe maritima), a perennial that is both ornamental and edible but borderline hardy in my garden. Where the climate is too cool to ripen peppers or eggplants, they can bask all season long in a large lantern cloche.

When selecting a cloche, one point to consider is how airtight it is. The less permeable a cloche is, the warmer the trapped air remains on cold nights. On the other hand, airtight cloches demand more attention to prevent overheating and possible death to your plants. I generally opt to forgo a few degrees of cold protection for the freedom of leaving my cloches almost unattended. This means leaving a block that vents an individual cloche in place overnight or leaving the top open.

If you live in snow country and are planning to protect vegetables well into winter, also consider how well your cloches will stand up under the weight of snow. Waxed-paper Hot Kaps will be crushed in a snowstorm, whereas glass or rigid plastic cloches such as the Aqua Dome can withstand an early winter snow.

Consider also the material from which the cloche is made and its durability. Some cloches, such as Hot Kaps, last only one season. Lightweight plastics used to make Wall O' Waters, solar umbrellas, and tomato plant covers may last up to five years with proper care. Rigid polycarbonate plastics used to make the Aqua Dome and lantern cloches should last for many years, especially if the plastic has been treated with ultraviolet light inhibitors and the cloche is stored indoors out of the sun when not in use. Glass is forever -- if it doesn't crack first.

Finally, consider what you'll do with the cloches when they're not in use. If your garage is like mine, it's already overflowing with shovels, flats, rakes, and other garden-related items. You might not want to figure out what to do with a gardenful of glass bell jars. Hot Kaps, on the other hand, get tossed out after only one season. Rigid plastic cloches such as solar bells and Aqua Domes can be stacked. Wall O' Waters collapse when drained, solar umbrellas fold up like an umbrella and tomato plant covers unfold and store flat.

Visit the web site of garden consultant and writer Lee Reich at

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