By Kathy Widenhouse, award-winning writer and owner of Tomato Dirt, a leading online source of for growing tomatoes in the home garden.
How do you know when to transplant tomato seedlings? You want a healthy crop. Yet there’s not a one-size-fits-all answer for transplanting tomato seedlings. Think of all the variables …
There are plenty of answers for each of those different scenarios. Here are tips to help you know when it’s time to transplant tomato seedlings of all stages.
If you start tomato seedlings in a seed tray – either one with cells or one without – you’ll need to transplant them into larger pots. A newborn tomato plant does not have a lot of room in a seed tray.
Tomatoes need that room in order to grow strong root systems. Plus, if you’ve started plants in a seed tray without cells, then there’s a good change that tomato seedlings’ roots will intermingle. The longer seedlings stay in trays, the greater the shock they’ll experience when you move them into their own “apartments.”
When tomato seedlings have 2 sets of leaves the second set is at least ½” long, it’s time to move them up to 3-6” transplant pots. You may need a bit of ingenuity in the process. If two tomato seedlings have germinated in the same cell or closely together, then use tines of a fork to separate stalks and roots.
Peat pellets are disks of dehydrated peat, held together by biodegradable fine mesh netting, that are used for starting seeds. The pellets are available in three sizes: 36mm (1.4 inches), 42mm (1.65 inches) and 50mm (about 2 inches). The largest size works best for starting tomato seeds.
And since tomatoes need lots of strong roots to be healthy and strong in the garden, it’s rare to place peat pellet seedlings directly in your garden. Instead, you’ll almost always need to transplant tomato seedlings from peat pellets into a bigger pot in the 3-6” range. Let the seedling accumulate branches, leaves, and height in these individual pots before beginning the process of hardening off.
Let’s say your tomato seedling is no longer a seedling … it’s a small plant. Your plant is root bound or it’s too big for your 3-4” pot. Yet it’s not yet time to set your tomato plants outdoors.
It’s time for something else – for transplanting tomato seedlings to a bigger container. Choose a pot that’s 2-3 times the size of your tomato’s current home – like a 6” pot or a quart container. But make sure your pot is no bigger than one gallon or else transplanting the seedling to the garden or to a patio container will be a significant shock.
You’ve transplanted your baby tomato seedlings to 3-6” transplant pots and over the last few weeks, they’ve flourished. They’ve got multiple branches and leaves. But how do you know when to set out your tomato seedlings into your garden plot?
Check your local extension or a region map. What is your area’s last frost date? Tomatoes are heat lovers. They do best when planted about 10-14 days after the last frost date so that the soil can warm further. Consult the calendar and calculate the optimum date to transplant tomato seedlings outside by adding 10-14 days to your region’s last frost date.
But before you move your tomato seedlings directly from their safe and comfortable indoor home on that magic date, prepare them for the adjustment. About 7-10 days before planting tomatoes outdoors, begin setting them outside in a protected area for a few hours at the time. Increase their exposure each day to help acclimate them to temperatures, sunlight, and wind. This process, called “hardening off,” helps prepare tomato seedlings for the shock of transplanting.
That means you can start the hardening off process right around the last frost date in your region – provided your tomato plants are ready.
The foundational rule of thumb for growing tomatoes in pots: from the outset, choose the biggest container possible for your plants. Tomatoes have large root systems. When you give them room to develop, they can flourish and produce.
That said, maybe you chose a container that was appropriate for a particular type of tomato, such as a 3-gallon pot for a patio bush tomato variety. However, as the season progresses, the plant clearly fills out the pot. You discover you must water it at least once and often twice a day, or it droops.
Those are indicators that transplanting to bigger pots is in order. Choose a significantly larger container than the original – at least twice the size. Make sure the pot has good drainage. Add plenty of rich soil and organic matter to the new container to make the change worthwhile for the plant. And then carefully extract the tomato plant with its entire root ball intact. Water thoroughly. And baby your plant for a few days with extra shade so it can adjust to transplant shock.
True, there’s an optimum to time to transplant tomato seedlings. Seedlings that wait to long to be transplanted turn into mature plants and get leggy. They may even put out blossoms. But unless your tomato plant has passed away, you still have the opportunity to transplant it.
Use the extra length to your advantage. Plant the stem deeply in a bigger pot or in the ground. The buried branch will sprout extra roots. With a bit of TLC (and some shade and extra water those first few days to ward off tomato transplant shock), your plant can thrive.
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