When you start your seedlings indoors, they are in very sheltered conditions. This is a very good and happy thing for them, as it allows them to devote their energy to sprouting and getting a good start growing. If they’re going to be transplanted outside, though, they need some help in developing the strength they’ll need to make that transition successfully, and you can start giving them a little extra help in that department as soon as they’ve developed their first set of true leaves.
When your seedling emerges from the soil, it will have a single leaf or pair of leaves called ‘seed leaves’. Think of them kind of like baby teeth- they’re there to allow the seedling to begin its journey to maturity, and are usually photosynthetic, but they’re not what are referred to as ‘true leaves’. Seed leaves will not develop into the shape that is characteristic of your mature plant- they are a transition mechanism between the stages of seed and plant. The next leaves that you see after the seed leaves are the first of the ‘true leaves’ and will develop into the characteristic leaves of your plant.
Once you see these true leaves, it is time to begin looking at ways you can help your seedlings become strong and healthy for their eventual transition to the outdoors. Most people know about ‘hardening off’ (which I’ll discuss later), but there is something you can do to help strengthen them even before you’re ready to start the hardening off process, and it’s very simple- either brush your clean fingertips across their tops a few times each day, so you’re just rustling their leaves a bit, or turn a low fan on them for 15-30 minutes at a time, 1-2 times per day (preferably changing the direction each day).
When your seedlings are growing indoors, there is likely to be very little in the way of breezes or wind, and that means that they could become ‘leggy’. All that means is that the stems are long and thin. While that may be a desirable thing for a human body in our culture, I can assure you that it is not at all desirable for a plant. Leggy stems are weak, and that means they could easily break or sustain irreparable damage from typical outdoor conditions. By brushing your fingertips gently across them or allowing a fan to mimic outdoor breezes, you are stressing them ever so slightly. That stress causes the seedling to put some energy into strengthening the stem and roots.
Now, if you’re growing tomatoes from seed, there is another trick to helping ensure they will grow into strong, healthy garden producers. When the true leaves on a tomato plant have grown, you will also notice a fine down of little hairs on the stem. All of these little hairs are roots that are just waiting to touch some dirt to develop. To get a strong tomato plant, you want to start with the best root system possible. Repotting the seedling into a deeper pot can help your tomato plant have a better, stronger root system prior to transplanting. You can safely put dirt up to just below the seed leaves, so don’t be shy about it- your tomato plant will thank you with a better yield of those lovely luscious fruits come harvest time! (Do keep in mind, though, that any time you disturb the roots, you’re traumatizing a tender young plant and it will need a few days to adjust to the new digs before experiencing any more trauma.)
Okay, so now your plants have nice strong stems, well developed true leaves, your tomatoes are in dirt up to their seed leaves, and you are thinking it’s going to be time to transplant them into their home outside very soon. Now what? The next step is called hardening off, and it is simply the process of gradually getting your seedlings acclimated to the outdoor conditions before sticking them out there 24-7.
I usually follow a schedule that involves a day or 2 of about 4 hours outside, during mid-day. Days 3 through 7-9 they go out as soon as I get up (okay, I’ll admit it- they wait until I’m done my first cup of coffee) and then come in just as the light begins to dim at the end of the day. They still get a couple more hours under the growing lights after that. Then, starting around day 8 to 10, they stay outside overnight. Somewhere around day 10 to 14, they get transplanted into what will be their permanent home. It can be tedious to carry them back and forth, especially if you’ve got several trays of seedings, but it is well worth the effort. Hardening off is crucial to the plant’s ability to make a healthy and successful transition into the garden, and healthy plants are less prone to attracting certain pests and developing certain diseases.
Oh, and don’t forget! Crush up some eggshells or add some other calcium booster into the soil where your tomato plants will go- the plants will grow more vigorously, produce a higher yield, and be less susceptible to blossom end rot (a nasty fungal disease that calcium deficient tomato plants are prone to.)
So, do you have any tips or tricks to helping plants grow strong and/or thrive after transplanting? Are there any easy soil add-ins you use or have heard of people using that help keep the plants healthy as they grow? I’d love to hear about it if you do!