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.