Preparing and Planting in Seed Flats

Choose your sowing medium carefully. It should be porous and well drained, but absorbent and soft as well. Textured humus or compost is fine. You definitely should not use dirt from the garden, as it can bring in disease and weed problems, and seldom provides the best consistency or drainage for starting seed indoors. Please see "What is the Best Planting Medium to Use?" for more detailed information.

1. For each 5-1/2 X 7-1/2 inch flat to be filled, dip out four cups of growing mix and place in a plastic bag. Add 1-1/2 cups of water at room temperature.

2. Close the top of the plastic bag tightly and gently squeeze the moistened growing mix to help it absorb the water thoroughly.

3. Put the moistened growing mix into a seed flat and run a flat piece of wood (a ruler is good) over the top to level off the mix even with the top edge of the flat. Pat it down gently, but add more mix if the level goes lower than 1/4 inch lower than the brim of the flat.

4. Make shallow furrows one inch apart in the surface of the growing mix, using a pencil, your fingers, or a wooden label cut to fit the flat. Make the furrows 1/4 inch deep for small seed, 1/8 inch deep for tiny seed. Large seed can simply be poked into the medium without making a furrow, though you will want to keep them in lines for ease of transplanting. For extremely tiny seed like Begonia and Calceolaria, which are almost like dust, it is best to evenly broadcast them over the surface of the growing mix, since their size makes planting in rows impractical. If your seed are hairy or cottony, plant them as they are, hair and all.

5. Make labels for each kind of seed you plant, and be sure to include the sowing date. No matter how good your memory, it will most likely not be up to retaining all the information about every seed you’ve planted, and you will need the name and date of sowing to determine when and where to plant your seedlings out in the garden.

6. The size of the seed will make a difference in how you plant them, so please see Preparing and Planting in Seed Flats, pgs 2 & 3, to read about the treatment of tiny, medium, and large seed.

7. Water the flat from the bottom. Place the flat in a pan of water at room temperature (cold water can slow germination) until the top of the medium is very moist. Bottom watering in this manner helps to prevent seed being washed away by the force of sprayed water, helps minimize disease, and is one of the best ways to keep the planting medium evenly moist, but not overly wet.

8. Cover the flat with a clear plastic sheet, or place in a clear plastic bag. The plastic should not touch the surface of the growing medium, so you can use toothpicks, labels, wooden dowels, or other small supports to hold it above your tray.

9. Place where the seed are to germinate. Most seed require good light for proper seedling growth, but do not place in direct sunlight. A waterproof seedling heat mat will greatly improve the performance of your seed, and I really recommend having a thermostat to control the heat so you don’t inadvertently burn or stunt your seedlings.

10. As soon as you see the seed begin to sprout, remove the plastic covering and move to higher light – filtered sun light on a windowsill, or under a grow-lamp is ideal. Your little seedlings might benefit from a short transition to the brighter light conditions. Start with three hours a day in the brighter area for a couple of days and then add three more hours every two days until, at the end of 5 to 6 days, you have them acclimated to the brighter area.

Tiny Seed (Impatiens, Begonia, Petunia)

a. For extra protection and easier handling, most quality seed companies package tiny seed specially in a see-through glassine inner envelope, which you will find tucked inside the regular seed packet. Remove the glassine envelope from the seed packet. Handle it gently by the edges to prevent crushing or breaking the tiny seed. Hold the glassine envelope with one side crease facing up, and tap the end with your fingernail until you can see the seed inside collect along the downward side crease of the envelope. Then snip the end off with scissors.

b. Press the edges lightly between your fingers to hold open the mouth of the envelope. Sow seed thinly by tapping the glassine gently with your finger. Seed should roll along the crease and out of the envelope in a single thin line. You can also use a seeder to make handling these tiny seed easier and more exact.

c. Sow the seed into the rows, but DO NOT COVER THE SEED because they may be to small to break through the growing medium. To keep evenly moist, cover the flat with a sheet of clear plastic, or enclose in a clear plastic bag, held off the growing medium by toothpicks or wooden sticks. This also applies to seed that require light for germination.

d. Many tiny seed are pelleted, or coated in clay, to make them big enough to handle separately. Treat pelleted seed like medium-sized seed.

Medium Sized Seed (Salvia, Pansy, Cabbage)

a. Shake or tap the packet to make the seed settle on the bottom. Cut the seed packet open across the marked line at the top.  A clean cut makes smooth sowing easier.

b. Pick up the packet with one hand, thumb on one side and fingers on the other. Press at the edges so that the packet stays open, and crease the packet at the center of the lower lip to make a trough. To sow seed evenly along the length of the furrow, hold the packet level over one corner of the flat, close to the surface of the medium at the end of the first furrow. Move the packet slowly along the furrow, while tapping the packet lightly with a pencil or your finger. A few seed should roll out into the furrow with each tap. If too many seed fall too close together, simply separate them with the point of the pencil. If you are doing this for the first time, it may pay to practice sowing over a creased piece of paper first, to see if you are sowing your seed the proper distance apart. There are also seed sowing devices that make seed sowing easier to control.

c. To cover the seed, use your pencil or stake to press the seed gently into their furrow, and then push a little mix over them from either side of the furrow. You can also pinch the furrows closed with your fingers. A good rule of thumb is to make sure the seed are covered to four times their thickness. (Note: Some seed like to germinate in full light without being covered, so skip this step for them.)

Large Seed (Morning Glory, Sweet Pea, Zinnia)

a. Hold the top end of the packet between thumb and forefinger, shake seed to the bottom end of the packet, and cut or tear off the top of the packet.

b. Pour the seed out into your hand; use your finger or a pencil or pointed wooden stake to poke each seed 1/4 inch deep into the prepared growing mix. Space 1 inch apart in rows 1 inch apart, so there is 1 inch of space surrounding each seed.

c. Sprinkle dry growing mix evenly over the seed if cover is required (see packet instructions, or the individual listing in the Plant Reference Section). Seed should be covered to four times their own thickness. Fast-germinating large seed should not be covered with plastic; those that germinate slowly do benefit from a plastic cover, applied so it does not touch the surface of the growing medium.


Gardeners' Quotes

Should you be a cottage gardener, a Victorian gardener, an herb gardener, a plain dirt gardener, a natural gardener, a container gardener, a colorist, or an enlightened combination of all sorts of specialist dogmas?  It is my contention that if you wish to succeed in the gardening life, there is only one true path to salvation-be a realistic gardener.
Eric Grissell, Insects and Gardens, 2001