(Note that this article does not apply to seeds that have been sown directly outdoors. They are already used to outdoor conditions.)
Your little seedlings have grown nicely, and are healthy strong little plants. Now it’s time for them to move outdoors to their permanent homes, in containers (or in the ground – the same principles apply), each according to its proper time. What I’m referring to by “each in its proper time” is that some plants are cool weather plants (lettuce, spinach, others) that can be planted outside early and others (tomatoes, peppers, eggplants, others) cannot go out until danger of frost is over or you are prepared to take some protective action on cold nights. The obvious protective action with container plants is to bring them inside. But in any case, the warmth-lovers aren’t really going to take off and grow much until the weather is warm. So you will not gain much by putting them out much before the last frost date.
Ideally, you would “harden off” your little plants before transplanting them to the outdoors. This means to gradually accustom them to the stronger light outdoors, the breezes or winds, and the fluctuating temperatures. This applies only to seedlings that have been grown indoors (under lights or in a windowsill) or in a greenhouse or hoophouse: in other words, they’ve been in a sheltered environment. If you just plop them outside in the strong sun, breezes, etc., they’re going to be very shocked, decline, and probably not thrive. They may even die.
“Hardening them off” is the ideal way to do this (but not the only way, as we will see later). It’s done by taking the seedlings outdoors for one hour the first day, then two hours the second day, and gradually increasing the time they are outdoors until it’s almost an entire day, at which time you can transplant them out. This takes a week or two and it takes cooperating weather, really, for most of a week. It cannot be done in rain, serious cold, or serious wind.
I’m sure some people manage to do it: but it just doesn’t work in my life. Even if the weather cooperates (which rarely happens), taking all the little plants in and out all the time is a real nuisance and more time and trouble than I want to cope with. And I’m home most of the time! I just cannot imagine how people who work away from home could possibly cope with hardening plants off.
But if you can do this: it’s the ideal way. If you cannot manage it, don’t despair. There’s another way, and I (at least) find it much easier and much less trouble and very successful.
For the rest of us….. you can *protect* the little plants for about a week after they have been transplanted out rather than hardening them off prior to transplanting out. I find this much easier. The idea: you want to protect them from some of the strong sun, the wind, the cold until they gradually become more used to the wide world of the outdoors. So, we’ll discuss transplanting them out first, then protecting them.
The perfect time to transplant your little plants out would be on an overcast day, or in the early evening, so they can recover a bit from being transplanted before the strong sun hits them. Absent the perfect time: transplant them when it’s convenient for you. They’ll manage if you protect them.
See my article on compost, soil and fertilizer for directions on preparing the container. Then you just scoop a hole in the potting soil. Water your little seedling, upend its pot or 6-cell pack, and encourage the seedling to come out of the pot or pack. I do this by squeezing the sides of a pot, or by scooping the plant, and its root ball and soil, out of a 6-pack (using a table knife or teaspoon). Then put the plant’s root ball in the hole you’ve scooped, fill in around it with potting soil, pat the soil down gently with your hands, and water and feed the little plant (use water containing plant food).
Note that most little plants should be transplanted to be at the same level as they were in their prior container: however, tomatoes benefit by being buried deep. This may seem strange, but if you snip off the lower leaves of tomato plants and bury the plant up to its top clump of leaves, it will form roots all along the stem and will benefit in the long-run, producing tomatoes sooner for you.
OK, the little plant is transplanted. Now to protect it for a while. If the weather is cool and the plant is small enough, you can use a milk jug greenhouse, made by cutting the bottom off a milk jug. If the plant is in a really breezy spot, I generally stick a twig (or a small piece of bamboo) down inside the milk jug and into the soil, to ensure that it doesn’t blow over. In really warm weather, I don’t like to use these as I think they might cook the plants.
In really warm weather or for larger plants, you can just shade your plant from the strongest (overhead) sun, and shelter it from the prevailing wind. You can do this by using a little chicken wire cage around the plant, and covering all or part of the chicken-wire cage with plastic. I like to use white plastic kitchen-sized garbage bags for this. They are cheap, and easily available. The (often white) plastic bags you get in the supermarket to carry your groceries home will work nicely for this task, too. I leave the protection there for a few days, then tear part of it away, to leave a partial covering. A few more days later, I’ll remove the rest of the covering.
Rather than a chicken wire cage, you can just use a few stakes or a few pieces of small bamboo (maybe even chopsticks!) to support the covering. Rather than using plastic for the covering, you can use a bit of white or light-colored fabric (old t-shirt, torn old pillowcase, etc.), or of course you can use floating row cover. Some people buy “hot-kaps” which are special little tents made of waxed paper. I have never used these, so I do not know how well they work. There are various other gadgets available and various other home-made contraptions.
As a container gardener, you might have an even easier way to do this: if you can put the container in a spot that is sheltered from the wind and in shade, that should be sufficient protection for the little plants. Then gradually pull the container into the full sun and normal amount of wind. I’d do this over the course of a week. This sounds fairly complicated: but it might be as easy as giving the container a little shove as you walk in the door each day after work. It’s one of the things that’s probably more time-consuming to write about than to do.
I also pay particular attention to keeping the soil moist when the plants have first been transplanted outdoors and need to get over their shock at being transplanted.
Now your little plant has been transplanted outdoors, protected, fed, watered, has become accustomed to the wide outdoor world, and is well on its way to maturity.