Seedlings will eventually run out of room in their original containers and must be thinned or transplanted before they become root bound or so interwined with their flat mates that you will never get them separated. Removing plants from their original flats or containers for transplant is called pricking out. Removing plants from a flat to a pot or a pot to a larger pot is called potting on. Some plants, like tomatoes and peppers, may be potted on 2 or 3 times before finally being transplanted into the garden.
Prick out seedlings when the first true leaves appear, or the second set at the latest. Young plants transplant better than older ones and suffer less from transplant shock. Water the seedlings the day prior to pricking out so they are moist and soil sticks to the roots. But don’t over water or they will be a sodden mess.
When pricking out use a widger, knife of other tool to carefully dig up the seedlings. Always hold the seedling by the cotyledons or true leaves, never by the stem. Leaves can grow back; stems cannot. Gently disentangle the seedling roots as necessary. If roots are hopelessly tangled, “block” the flats by cutting lengthwise and crosswise with a knife as if cutting brownies. Then lift the blocks for replanting. All but the strongest seedling will be thinned out later.
If potting up, turn the pot upside down holding the seedling between your fingers without touching the stem. Gently tap the pot bottom until the seedling drops out. Make room for the roots in the planting hole. Don’t coil them to fit the hole or container. If they don’t fit make a bigger hole or use a bigger container. Snip off the cotyledons and set the plant in the hole almost up to its first set of true leaves. Carefully fill in the hole with soil and firm it gently. You want to ensure soil contact with the roots but you don’t want to damage them.
Water lightly, then set the transplanted seedlings in indirect light for 24 hours to let them recover from their ordeal.
Pricking out and potting on can be a tedious chore, but focus on the dozens of beautiful little seedlings that you are taking from a single flat. With good care they will flourish and you will have a variety of seedlings that would have cost you hundreds of dollars at a nursery, all for the cost of a few seed packets and a container of growing mix.
Special tip: although thrifty gardeners do use various items like knives or spoons for pricking out, nothing works better than the proper tool - which is a widger. You can purchase a widger from Bountiful Gardens, located in Ukiah, for $5.00 plus shipping (order some of their heirloom and organic seeds at the same time), or get one at the Common Ground garden shop in Palo Alto. Common Ground has other great gardening tools to choose from and you can also purchase seeds, organic fertilizers, amendments, and plant starts.
Be sure to read the final article in the grow your own seedling series: Hardening off.