Although they have largely been replaced by plastic row covers and hoop structures, the traditional bell jar in the garden is still a beloved way to aesthetically (or cheaply) cover plants to extend a growing season or fend off early (or late) frosts. Bell jars can be purchased or made of both plastic and glass and many gardeners save money and make their own by re-purposing other plastic containers.
Benefits of the Bell Jar
Bell jars allow for earlier planting, faster germination, frost protection, water conservation, pest protection, and often lead to an increase in yields because of this.
Because bell jars protect against frost and create a miniature greenhouse effect within, they can allow earlier planting and often speed up seed germination by keeping the top layer of soil warmer. During the plant’s growth, water is conserved due to this same greenhouse effect with the moisture from the plant no longer being lost to the surrounding air outside.
Pest protection is obvious thanks to the physical barrier the bell jar creates around the plant. Yields are increased due to all of these things helping to build a stronger, better plant.
Using a Bell Jar in the Garden
Bell jars can be used on just about any plant, especially in the early germination and growth stages. Most plants will likely outgrow all but the most colossal of bell jars, but if the jars are used to cover smaller plants, they can extend harvests into the late fall or early winter without trouble.
Often, bell jars are also used to create small greenhouses to grow plants that would otherwise not thrive in the current climate. Bell jars are also used indoors to protect plants from children and pets or from drafts that might exist due to air conditioning or doors and windows.
Finally, bell jars are often (especially today) used as decorative items to cover arrangements of fresh or dried flowers, decorative plants, etc. This is the most common use of glass bell jars.
Plastic vs. Glass Bell Jars
Which to use depends on the intended use and the availability of the jars themselves. Plastic is much cheaper and easier to find today, so most bell jars in the garden are likely plastic. They are also easier to manufacture yourself by re-purposing other common items into bell jars.
Glass has the advantage of better insulation and generally stronger structure. It’s also more traditional and less likely to blow over (or away) or be knocked over by animals or birds. Glass also does not break down under solar exposure as plastic will eventually do.
The chief disadvantages of plastic are: it is light weight and eventually breaks down due to solar radiation. Plastic leaching is also a concern for many gardeners. Glass has disadvantages as well, including susceptibility to breakage and high expense.
Plastic bell jars can be created out of 2-liter soda bottles from which the bottoms have been cut off, from some types of planting pots, from readily-available containers and other items. Thus, plastic bell jars are a favorite amongst DIY and low-cost garden enthusiasts.
Glass bell jars are usually purpose-made and are often hand-blown. Many are purely decorative, but functional glass bell jars are still readily available to the gardening market.