Some winter sowers plant just a few winter sowing containers but sow the whole packet of seeds because they don't see how more than a few could possibly survive. Others get carried away and plant hundreds of soda bottles, milk jugs, and other containers in an effort to winter sow every possible seed in their stash. But no matter how they get there, many enthusiastic winter sowers reach a point where they look out at a sea of 10,000 spring sprouts and wonder what they can possibly do with all those tiny plants. Don't panic!
As soon as seedlings start getting their first set of true leaves and the weather starts warming up, you'll want to harden off your little plants to get them ready to transplant. Although being grown outside means they're already halfway hardened off compared to plants grown inside under lights, winter sown seedlings have still been sheltered by the greenhouse like environment of their enclosed containers. Exposing them gradually to increased amounts of wind and sun will keep them from going into shock.
Seedlings can go directly into the garden from their winter sowing containers, or they can be potted up to grow a little bigger first. The choice depends on the type of seedling and on your own gardening style. Many winter sowers never pot up any of their seedlings, and they tell me I baby my plants needlessly. However, my success rate seems better if I grow seedlings on for a while in pots before planting them out. An in-between option would be planting winter sown seedlings in a nursery bed, where you can keep a close eye on them.
Those who plant their seedlings directly out into the garden usually use the HOS or "Hunk ‘O Seedlings" method. With this method, do not prick out tiny individual seedlings to transplant into the garden. Instead, transplant large clumps of seedlings as a group. The tangle of stems gives the plants structural stability, and the larger mass of roots makes them better able to take up water from the surrounding soil.
For those faced with 10,000 spring sprouts, an additional benefit of the HOS method is that an entire container of winter sown seedlings can be divided into a few hunks for planting. Upending a milk jug filled with seedlings into the palm of your hand and then quartering the rootball will give you 4 large hunks of seedlings, for example. There's usually no need to thin the seedlings after planting out the HOS. Competition means that the strongest seedlings will survive.
I find that when I put tiny seedlings out into the "wild blue yonder" to fend for themselves, I simply don't pay enough attention to them. More often than not, they end up getting overrun by weeds, eaten by bunnies and slugs, or dried up when a splash from the hose would've saved them. Except for a few plants (like poppies) best planted out as tiny seedlings before they develop tap roots, I up-pot nearly everything I winter sow.
Winter sown annuals may only get potted up briefly in cell packs, giving them a chance to form really good roots before planting out. Perennials usually get potted up in quart or gallon pots. By fall, they'll have nice root systems, and I'll plant them out into the garden. I'll often overwinter potted perennials seedlings in a sheltered location for planting out the following spring. It does make for a lot of watering of pots over the summer, but I get a lot of sturdy plants for my garden with this method.
Potting up is also useful if you're trying to maximize the number of plants from your winter sown container. I often winter sow plants such as dianthus or alpine strawberries that I want to use for a border, which means I'd like to have a flat or two of plants. If I use the HOS method, I may only be able to divide my container into 6 or 8 clumps of seedlings. But by transplanting clumps of just 2 or 3 seedlings into each cell of a 36 or 48 cell flat, I can turn that one winter sowing container into many more plant divisions.
I use a good quality soil-less potting mix for potting up seedlings. Adding time release fertilizer provides nutrients for strong growth. I generally use a 3 month fertilizer such as Osmocote (14-14-14) for plants that will stay in containers until this fall. For plants that will overwinter in their containers, a 9 month fertilizer such as Dynomite's general purpose 13-13-13 might be a good choice.
Regular water from rain or a hose is crucial to good growth of plants in containers. Polymer moisture crystals can be a tremendous help in keeping moisture levels more even. Follow the application instructions when adding the crystals to your potting mix–more is not better!
Don't get overwhelmed by that wonderful abundance of greenery in your winter sowing containers. Start dividing the seedlings into hunks, either planting them out or potting them up. One or two containers at a time, just get started and work your way through them. Before you know it, your sea of winter sowing containers will dwindle, and your garden will start looking lush. This fall and next spring, you'll be able to "shop" among the pots on your patio rather than at your local nursery.
Turn 10,000 spring sprouts into an abundance of wonderful new plants for your garden!
Photos by Jill M. Nicolaus.
(Editor's Note: This article was originally published on May 15, 2008. Your comments are welcome, but please be aware that authors of previously published articles may not be able to promptly respond to new questions or comments.)