The practice of covering a raised garden bed is a technique for actively managing the growing environment. Raised beds themselves offer advantages like improved drainage and warmer soil, and adding a cover can substantially amplify these benefits. By creating a controlled microclimate, gardeners can significantly extend their harvest periods, protect vulnerable crops, and manage external threats. The strategic use of various covering materials transforms a simple raised bed into a more sophisticated system for year-round cultivation.
Determining the Purpose of Covering
Defining the specific objective for covering the bed is necessary, as the goal dictates the required structure and fabric. One primary reason is season extension, using covers to warm the soil for earlier planting or shield crops from frost for later harvesting. This temperature manipulation allows for successful cultivation outside of the natural growing window.
Another common purpose is pest exclusion, where a physical barrier prevents insects, birds, and small animals from accessing the plants. This management method avoids chemical treatments by blocking the threat. Finally, covers can be deployed for soil preparation, notably through weed suppression or solarization.
Constructing Covers for Climate Control
Covers for climate control, such as frost protection and season extension, require a robust structural framework to support heavier materials and withstand weather. The most common structure is the hoop house or low tunnel, built by bending flexible material over the bed to create a series of arches. Materials like half-inch electrical metal tubing (EMT) or half-inch PVC pipe are commonly used for this purpose.
These hoops are anchored by slipping the ends over short pieces of rebar driven into the soil or by securing them directly to the bed frame. Clear polyethylene (PE) plastic sheeting is a popular choice for maximum heat retention. This plastic traps solar energy, creating a greenhouse effect that can raise soil temperatures by 10 to 15 degrees Fahrenheit above uncovered beds.
For a more permanent structure, a cold frame involves building a box with a hinged or removable top made of glass or twin-wall polycarbonate. This offers better insulation than single-layer plastic. Alternatively, heavy-duty fabric row covers, typically non-woven polypropylene, provide substantial frost protection without the high humidity associated with plastic. A heavyweight cover can provide an insulation benefit of approximately 6 to 8 degrees Fahrenheit, preventing damage during hard frosts while still allowing air and water to pass through.
Barrier Methods for Pest and Weed Management
When the objective is to exclude biological threats, cover materials focus on being light-permeable and non-heating, requiring less structural support. Lightweight floating row covers, often spun-bonded polyester, are ideal for insect exclusion, including pests like cabbage moths and flea beetles. These covers can be placed directly over the plants, though using hoops is preferable to avoid plant contact.
Fine mesh netting provides a barrier with better airflow than fabric row covers, useful in warmer weather when heat buildup is a concern. The mesh size is calibrated to block specific pests while allowing sunlight and rain to reach the plants unhindered. These methods are effective when applied immediately after seeding or transplanting to prevent pests from establishing populations.
For managing weeds or sterilizing soil, opaque or clear plastic is applied directly to the soil surface. This process, called soil solarization, is most effective during the hottest part of the summer, requiring four to six weeks of high temperatures. Clear plastic is used to trap solar energy, raising the soil temperature to a lethal range of 120 to 140 degrees Fahrenheit, which kills many weed seeds and soil-borne pathogens.
Installation and Maintenance of Covers
Effective installation requires securing all edges to maximize the cover’s utility and prevent wind damage. For hoop structures, the cover material should extend several inches beyond the bed’s sides, where it can be secured using spring clips to hold it firmly to the hoops.
The excess material at the base must be weighed down to create an airtight seal that prevents pests from crawling under or wind from lifting the cover. This seal is necessary to prevent pests from crawling under or wind from lifting the material. Common securing materials include:
- Soil
- Sandbags
- Bricks
- Specialized ground staples
For any enclosed cover, especially those using plastic for climate control, managing ventilation is a constant requirement to prevent the internal temperature from exceeding safe levels. Temperatures inside a cold frame can rise rapidly on a sunny day, even when outside temperatures are low, potentially overheating and damaging plants. The cover must be opened or propped up when the interior temperature rises above 50 degrees Fahrenheit, often requiring daily manual adjustment in spring and fall.
Proper removal and storage extend the life of the materials when the cover is no longer needed. Row covers and plastic sheeting should be thoroughly cleaned, dried completely, and folded or rolled up to prevent mildew or rodent damage. Storing these materials out of direct sunlight in a dry place ensures they remain viable for use in subsequent growing seasons.