Seed starter trays are a great way to promote seed propagation and control the environment needed for seeds to sprout. Seeds planted directly in the ground are susceptible to rain runoff, temperature variations and bird and animal foraging. Trays isolate the sprouts within the cells and allow tender plants time and the conditions they need to blossom. Starter trays can be purchased from home and garden vendors, home improvement stores, trade shows and online. Some models have moisture control pads and humidity regulating devices.
A standard tray has two parts. The lower part has a ribbed bottom so that water does not pool beneath the peat moss cells. The second part is a transparent or clear plastic lid. If not provided at purchase, fill the tray with peat cells.
To compose a good seed soil, blend thoroughly in a bucket one part vermiculite, one part sterile peat moss and one part potting soil. This mixture allows new roots to penetrate through the soil with ease. After blending, grab a handful and squeeze. It should be light, moist and have a degree of elasticity.
Pack the soil mix firmly into the cells to where it has a sponge-like feel. Leave ½" clearance at the top.
Place the seeds, only one or two per cell, gently on top of the soil. If the tray is not filled with all the same seeds, write a seed schedule to identify the seeds of each cell.
Read the seed package requirements. Different types of seeds have different fill requirements. Some seeds need no soil coverage to root. Many seeds need very little, 1/4-inch at most, soil coverage.
Use a squirt bottle to soak the cells thoroughly. Pouring water on the cells moves the seeds around and sometimes washes them out of the cells. The mist setting on a squirt bottle assures a steady flow and saturates both the cells and the soil. Use fresh rainwater if possible.
Poke seeds that have reemerged after soaking beneath the surface. Cover lightly with soil and squirt again. Tape two opposing sides of the tray down so that the cover does not blow during high winds.
Place the tray in a position of filtered sunlight; beneath a tree or under a covered deck is ideal. Direct sunlight builds up too much heat too fast. Keep cells moist and allow air to occasionally circulate through the tray.
Check the germination schedule. Some seeds (radishes for example) will sprout within a week, while others may take 21 days. Once seedlings start to show, they will want to take off. When they reach two or three inches, cut cells from the tray.
Prepare a new home in the garden. Use a sharp knife to cut away cells from the pack. The cells are moist and easy to cut, so make precision cuts without disturbing the other cells.