Garden fabric, aka row cover or floating row cover, can be very handy to have on hand in your garden, as it can serve many purposes!
Garden fabric can . . .
* slow evaporation from a plant and its surrounding soil
* act as a thermal barrier, protecting plants from the cold and the wind
* help to shade the plants, protecting them from overheating
* prevent insect damage, by keeping munching insects away from the plants
* stop birds and other critters from helping themselves to your harvest
* control pollination, in case you want to try very specific cross-pollination experiments
Available in different thicknesses, the heavier garden fabrics are better in the colder months (for heat retention), while the lighter fabrics are a much better choice when the weather gets hot.
Also, remember that many vegetable and fruit crops require cross-pollination and, since the fabric will limit access to the plants' flowers, pollination must be done by hand, or the fabric must be removed for an hour or two each day to allow pollinators to do their job. Once pollination has taken place, the row cover may be left in place to protect the maturing crops.
In some cases, garden fabric should be cut into strips, and the strips wrapped around the stems of plants to protect them from boring-type insects. E.g., most types of squash are susceptible to attack by the squash vine borer (SVB). As the name states, the SVB (in its large caterpillar form) bores its way into the main stem of squash plants, and then eats its way through the stem, usually until the plant wilts and dies. This attack may be prevented with a garden fabric wrapping of the stem. The best time to apply garden fabric in this manner is before a seedling is put in the ground. Start wrapping the stem about an inch below ground level, and wrap it all the way to the top, avoiding the side branches as you go. As the plant grows, more fabric may be added, and the fabric already in place may need to be loosened to avoid restricting growth of the stem. In this way, the stem is protected from vine borers, but the entire plant does not have to be covered, thereby using much less fabric.
For more info on this very versatile tool, see: www.gardeners.com/Row-Covers/5111,default,pg.html