A seed row cover is a thin fabric you lay over a bed right after you plant seeds. The cover holds in soil moisture and keeps the surface warm so seeds sprout faster than they would in open dirt. Most are made from spun-bonded polyester and weigh less than half an ounce per square yard. You can drape one straight on the soil or float it on light hoops above your bed.
I tested a germination cover on carrots last spring and the results blew me away. The covered row sprouted in eight days while the bare row took fourteen days to show green. I tried the same trick on beets and got the same fast jump. My radish patch under cover came up so even I almost did not need to thin the plants out at all.
The fabric works on two fronts at once for your seeds. First, it cuts surface evaporation so the top inch of soil stays damp through the day. Seeds need steady moisture to crack open and push out a root. Second, the cover traps heat from sun and soil to keep the bed a few degrees warmer overnight, which speeds up germ time.
Lightweight fabric is the right pick for fresh seeds in your bed. Per Maryland Extension, a 0.45 ounce per square yard cover transmits 90 to 95% of sunlight, which is plenty for young sprouts to grow. Heavier covers cut too much light and can slow your seedlings down once they break the soil surface.
You should choose a moisture retention fabric that breathes well so water still passes through when you irrigate. I water right over the top of mine with a wand sprayer and the fabric soaks the spray right down to the soil below. Skip plastic sheets because they trap too much heat and can cook your seeds on a sunny day.
Anchor the edges with soil or rocks so wind cannot lift the cover and dry out your bed. I use U-shaped wire pins every few feet along the sides to hold the fabric tight to the ground. This setup takes me about ten minutes per bed and pays off with stronger germ rates every single time I plant a new crop.
Pull the cover off at the right moment to avoid bent or crushed seedlings later on. For root crops like carrots and beets, take the lightweight row cover off when the first true leaves form on top. For lettuce or greens, lift the fabric once seedlings touch the underside. Wait too long and stems will twist sideways looking for more space and light.
Save your seed cover after you pull it and store it in a dry spot for next round. A good fabric will last three to four seasons if you handle it with care between uses. Fold it neat and keep it out of direct sun when not in the bed. You will get faster sprouts year after year for very little cost or work.
Read the full article: Row Cover Garden Guide: Weights and Timing
