I sowed my tomato seeds a few weeks ago and they're strong enough to move (see my blog, "Growing Tomatoes From Seed"). The first set of leaves that appear on a new sprout are the cotyledon leaves. They begin the photosynthesis process and get the plant growing. Typically they're oval shaped and don't look like the leaves of the adult plant; that's why it helps to label your seeds so you know what's growing. Soon after, true leaves develop. At that point there is enough root growth to support the plant and avoid the stress of transplanting. Wait for one or two sets of true leaves before transplanting.
|Lots of seedlings ready for transplant|
To begin, fill the new containers with fresh, sterile, moist, potting soil. Place the new pots and old pots together on your workspace. You don't want to be walking across the room carrying a tender seedling. Keep all of your activity confined to a small area.
Using a fork, a chopstick, a spoon, a popsicle stick, a knife, or any other small utensil, gently dig out out the seedling or group of seedlings that you are ready to move. Try to dig deep enough that you don't disturb too many of the young roots. Digging out the seedling with a clump of soil attached is fine.
|Digging out a clump of seedlings|
If there are multiple seedlings in the same clump, lay them down on a clean surface and gently pry them apart. Try not to tear the little roots. I use a wooden skewer for this. Gently grasp one or more of the seedlings with the tips of your fingers. It's important that you hold them by the leaves. Don't grab the stem! Pulling or holding these young plants by the stem can crush it and cut off all nutrients. This is a primary reason some transplanted seedlings don't survive the process.
|Gently separating seedlings|
Dig out a small hole in the new container and gently place the seedling in it. I use the same wooden tool to rough up the soil and then cover the roots lightly while I support the seedling with my fingertips. Most seedlings should be planted at about the same depth as in the old pot. For tomatoes you can plant them deeper because roots will develop along the buried stem and help make a stronger plant.
|Placing a seedling in the new pot|
I always sow more seeds than I'll use in my garden. I also transplant more seedlings than I know I'll plant. When I move them to a new pot I'll put two or three in the same one. This helps ensure that at least one plant will endure the stress. I may be overcautious because I rarely lose a plant. What results is multiple plants growing strong and I choose the strongest, removing the weaker ones.
|From seven pots to 19|
After the seedlings are in their new homes, water all of the pots, old and new. If you're using fluorescent grow lights, go ahead and put all of the plants back under the light. If you're growing on a windowsill, keep the plants out of direct sunlight for a few days while they adjust to their new pot.
|All of the seedlings back under the light|
If you moved them to bigger pots they won't need to be moved again until they're ready to go outside. If they begin to outgrow the new pot before the weather cooperates, you can repeat the transplanting process again by choosing a new, bigger pot.
That's all there is to it. Transplanting seedlings will double or triple the amount of space required to store them, maybe more. Anticipate where you'll put the new pots before you begin the process. If you don't have adequate light for all seedlings, it may be better to leave them in the original pot and just thin out the smaller seedlings. That's one reason I recommended starting seeds in pots and avoiding transplanting.
With proper water and light all of the seedlings will continue to grow and be strong enough for the garden soon. I'll cover that step in a few weeks.