Congratulations. You are the proud parent of a tray (or more) of baby plants. Remember, though, with parenting comes responsibility.
Once your seedlings are up and growing, they’ll require almost daily attention. If your potting mix did not contain fertilizer, you’ll need to start a feeding schedule. Wait until the first true leaves appear. (The initial “seed leaves” are the cotyledons, which contain plenty of food to get the baby off to a good start.) Use any liquid all-purpose fertilizer at half-strength, twice as often as the directions tell you.
And speaking of water, don’t let them dry out! At this stage, wilting is fatal, Even if your plants survive, they will suffer the effects of this trauma all their days. The ultimate crop yield will be smaller, and won’t taste as good, compared to plants that grew unchecked. Continue to water from the bottom, using water that is room temperature or lukewarm. You don’t want to shock their little roots with ice water!
If you planted more than one seed per cell, you may need to do some thinning. Grit your teeth and pinch or snip off all but the most vigorous seedling. One healthy plant is much better than two crowded ones competing for the same resources.
If you are growing under lights, keep adjusting the distance from the bulbs as the plants get taller. You want to keep the lights as close as possible without touching the leaves. With the exception of lettuce and spinach, your veggies will thrive on 16 hours of light per day. (As I mentioned previously, lettuce and spinach will respond to such long days by flowering, so limit their light exposure to no more than 14 hours. The other plants will do fine on 14 hours, so there’s no need to separate them.)
If you are using a windowsill, turn your seedlings regularly. Otherwise, they’ll bend toward the light. Make sure they aren’t being fried on sunny days, or frozen on cold nights. It helps to keep their leaves from actually touching the glass.
In the absence of wind, stems can grow lanky and soft. A fun and easy way to solve this problem is to pet your plants. That’s right, gently run your hand over the tops of the seedlings a couple of times a day. Bending their stems a little will result in stockier transplants.
Eventually, your plants will begin to outgrow their containers. Look for roots growing out the drainage holes. Or slide the plant part way out of its pot. Are roots filling the space? It may be time to move them into their permanent spot in the garden. But don’t just grab your tray of tender babies and head outside. First, they need to toughen up a bit to withstand the rigors of outdoor life. This two-week process is called hardening off.
Wait for a mild day to introduce your plants to the real world. In the meantime, stop using fertilizer, and cut back a bit on the water. You don’t want your seedlings to wilt, but keep the pots on the dry side.
Sunlight is much brighter than the lights your plants are accustomed to. Therefore, start by carrying your seedling tray outside and setting it in some light shade for a few hours. A light breeze is fine, but shelter your babies from anything that will cause damage. Now bring them all back inside and let them rest. Repeat the process over the next several days, gradually exposing the plants to more and more direct sunlight, and leaving them out longer and longer. Be poised to rescue them should the weather become too severe. After a couple of weeks, your transplants will be as ready as possible to handle whatever Mother Nature can throw at them.
If you aren’t ready to move your seedlings into the garden, they may need to move into roomier quarters. Use pots that are only slightly larger than the ones they are currently growing in. If you started your seeds in typical nursery four- or six-packs, try moving them to recycled 8-oz. yogurt cups, or 8-oz. plastic cups. (Don’t forget to add some drainage holes.)
Water the seedlings to ensure that the potting mix keeps its shape when you slide the plant out of its container. With most crops, keep the plant at the same depth at which it is currently growing. However, with tomatoes, peppers, and eggplant, you can set the seedling deeper in its new pot, adding mix around the stems up to the first leaves. They have the ability to grow new roots along the buried stem, making for a heftier root system.
Partially fill the new container with potting mix. You can use more of the same mix you started the seeds in, or regular potting mix. Carefully slide the seedling out of its pot and place it in its new home. Add potting mix around the edges to fill the space. Water to settle the mix and you’re done. Don’t try to compress the mix around the plant; you need those spaces for air and water!
The two photos on the left show a cell pack of tomatoes that are feeling crowded, and a tomato seedling planted up to its seed leaves (cotyledons) in a larger pot. Don’t forget to keep the label with the plant!