So, you’ve planted tomato seeds (Part 1) and are nurturing them along with appropriate levels of light and water (Part 2). If you followed my advice and planted two or three seeds in each growing cell, you will likely have two or more seedlings coming up in each cell.
You may have to brace yourself for the next step. You need to thin out all but the strongest plant in each cell. If you let more than one seedling grow in each cell you will have two plants competing for a small amount of resources.
The best way to do this is to use scissors and snip off the seedlings you don’t want near the base. This causes less disturbance to the roots of the remaining plant than trying to pull it out.
A single healthy seedling in each cell is what you’re after:
Grow them on, paying careful attention to providing adequate water, light and wind/stimulation until the plants and their roots start to outgrow their cells, which will take a few weeks.
The way I determine that the time is right to move the plants to bigger quarters is when I start to have difficulty keeping them adequately watered (i.e. I water them in the morning and they’re dry and thirsty again by evening) or when they’re jostling each other to get to the light (i.e. tray is crowded). Seeing roots on the top of the soil is another sign that they’re out of space and ready to move on.
At this point I water them once more, then use an old table knife or a flat-headed screwdriver to gently wedge each plant out of its cell, taking care to not damage the plant or its roots.
I then place the plant in a small pot (measuring about 4″ across the top), and fill the pot with potting soil. If you don’t have any pots available, you could use an old yogurt or cottage cheese container or even one of those red party cups–just make sure you punch several drainage holes in the bottom first.
Tomatoes will sprout extra roots along any portion of the stem that is buried in soil so they should be planted deeply. I like to put them to a depth so that the soil stops just below the first set of leaves.
If you’re growing more than one kind of tomato, label the plant pot with the name of the variety immediately.
Repeat with all of the tomato seedlings you have, water well, and place back under lights.
Continue to nurture with appropriate light, water and wind until you are ready to harden them off.
Hardening Off Tomato Plants
Tomato seedlings live a coddled existence. They cannot transition straight from the cushy confines of interior life into the garden without getting them used to the outside world. Transplanting them directly from inside without hardening them off will likely result in their death. At the very least, the leaves will become scorched and the plant’s growth will be set back considerably.
To help plants adjust to life outdoors they need to be gently introduced to the outdoors over the course of about a week. When the seedlings are big enough and there is a nice warm day they should be brought outside and placed in a shady spot that is sheltered from the wind for an hour or two, and then brought back in.
This should be repeated for a couple days, gradually extending the length of time they’re out and moving them from a fully protected area into direct sun and exposure to light wind. Remember that temperatures dip at night, so make sure not to forget them outside when you turn in for the night. Seedlings can be considered to have been fully hardened off when they are able to stay outside in a sunny, unprotected position for the better part of a day with no ill effects.
As soon as it is safe to do so (i.e. there is no more danger of frost), they can then be planted out, following the instructions in this post.