In the Beginning
Potting Up and Hardening Off
Part 6 of 8
Now that your seedlings have reached a few leafsets high, it may be time to transplant them into larger containers before their roots outgrow the little cells you had started them off in. A good rule of thumb to go by is their height. If the plant is more than two times taller than the container it is in, it’s time to pot up to taller and wider pot. (If you see roots coming out of the bottom of the cells, it is definitely time to pot up!) A twelve-ounce container or larger is a good size to use. Be sure that the container has adequate drainage through the bottom.
If you have leggy or lanky stems at this stage, here is another opportunity to correct that problem and build healthier roots. There are a couple of methods. The first is to bend the main stem into a “J” shape and carefully bury the hook part of the stem under the soil level. This takes up extra stem space and builds more roots off of the stem that is planted under the soil.
Another method that works very well if you have a lot of stems to work down into the pot is the “spiral”. This one is a bit trickier, if you’re not careful you could snap them stem. Just as it sounds, you can gently spiral the main stem down into the sides of a larger pot, making sure the main stem comes up the center of the pot and then fill in with soil. After each of these two methods of transplant, I recommend a light feeding of half-strength liquid fertilizer with higher potassium and phosphorus which will help build strength in the root system and keep them from becoming stressed. (My fertilizer of choice is Espoma “Bloom!”.)
After two to four weeks in their larger pots, your seedlings may be ready to be planted outside, but there is one more important step to take before putting them in the ground- hardening off. This is the process of acclimating them to full exposure to the sun. For two to three days, place your seedlings in filter sunlight/shade for three or so hours a day, then bring them back in under the lights for the rest of the day. Then for another few days place them in full sun for a few hours before bringing them back under the lights. Continue to add to their sun exposure for a few more days, taking about a week to fully acclimate them to the full strength of the sun.
If you skip this important step, your plants can be sunburned, which looks like a larger tan, dehydrated spots on the leaves and stem. Most plants can survive a sunburn, but it will set them back quite a bit as they take time to recover, while properly hardened off plants will be thriving and getting ready to produce.
Please check back soon for the next article in this series!