A reader, and good friend, emailed me to ask about steps to take with her seedlings. Here are her questions:
I've started most of my herbs (basil, thyme, oregano, sage, rosemary) and a few flowering plants (dianthus and forget-me-nots) indoors. My seeds are all sprouting and doing well. So, I'm thinking now what? How long can they survive in those tiny little seed-starting pods? Do I transplant them into a larger container before hardening them and putting them in the ground or is that an extra step that'll stress them out? What should I be looking for to know when they're ready to go into the ground?
Since this is my first time doing anything from seed, I feel like I need some guidance with knowing when and how to take the next step and would greatly appreciate you sharing any of your wisdom on the subject! :)
First of all, all plants are different and any special directions on seed packets should be followed. However, there are general guidelines that I've found work most of the time.
When: If you start your seeds in something very small, like a peat pod or those small cell packs, you'll usually need to repot the seedlings before they go in the ground. I try to do so when the seedlings have a couple true leaves (the second set of leaves, not the first set that emerge from the soil). Until then, the plant doesn't really need the nutrition of potting soil because the first set of leaves are actually a food source for the seedling. Another sign to watch for is roots growing out of the pod/container. Repot as soon as you start seeing roots. Waiting too long can result in a root-bound plant or roots that have gotten tangled in the netting of your peat pod.
How: Be gentle with your seedlings as you repot and you should be able to avoid stressing them out too much.
For peat pods, gently tear or cut away the netting that surrounds the peat. If the roots have gotten tangled in the netting, cut away as much netting as you can without damaging the roots. You don't want the netting to restrict new root growth, but it's perfectly fine to leave a little if it's tangled in roots.
For seedlings in plastic containers, very gently massage the plastic in order to loosen the seedling from its little home. Then, place your hand over the soil and grasp the very base of the seedling, turn the whole container upside down, and let gravity help you as you gently gently gently pull the seedling out of the plastic.
If you've used something biodegradable, like a toilet paper tube, small newspaper pot, or small Jiffy Pot (though, Jiffy Pots are usually big enough to last a while), then this is going to be easy-peasy. These can just be gently placed right into the next container. Unless you can tell it's already breaking apart, it can also help to "open" the old biodegradable container first so your plant's roots can spread more easily. With the toilet paper tubes, I usually pull back the bottom folds so that it's open. With Jiffy pots, gently cut or tear away the bottom. Newspaper is probably less of an issue, unless you've made a very thick paper pot. Note that if you know a plant you're growing doesn't handle transplants very well (like cucumbers or peppers), it'll probably be easiest to opt for one of these biodegradable options for the least amount of stress.
Exceptions: Sometimes I'll keep small plants in their toilet paper tube or peat pods until transplant, usually if they're small plants in the first place. Strawberries from seed, for example, tend to stay small until they're outside in the sun. I just watch the roots to make sure they aren't outgrowing their homes. However, I also add some extra nutrition by occasionally spritzing them with liquid Terracycle.
Also, if you're determined to jumpstart a plant that is so sensitive to transplanting that they're supposed to be direct seeded into the garden, you should at least start them in a sizable biodegradable container so there's only one simple transplantation to be done.
Deciding When to Put Them in the Ground
This has more to do with temperature and seasons than anything else, so read your seed packets. They will usually say something along the lines of, "Transplant outside after the last frost date" or "Transplant after danger of frost has passed." In Oklahoma City, that's April 15th... but you still need to check the weather forecast and use common sense, because the "last frost date" is an estimate. Learn more about that date here.
Aside from that, I don't like to transplant seedlings until they have at least 3 or 4 true leaves (or are strong looking, if true leaves aren't a consideration such as with green onions). And you should never transplant without hardening off first. You can google for detailed instructions on hardening off, but the basic idea is to expose your plants to an outdoor environment little by little. I start with an hour, then a couple hours the next day, then a few hours, then all morning or afternoon, then all day a couple times in a row. Just make sure you pick mild days and keep them out of the wind until they're strong.