Sometimes seeds will sprout and the seedlings will chug along for a while and then seem to stop growing. Here are possible reasons why, and what to do:
Seedlings not developing because conditions are too cold. Seedlings of heat-loving plants (such as coleus, zinnias and peppers) may stall if the air temperature is not warm enough. Boost the heat or move your seedling setup to a warmer room. Or bide your time and they will likely accelerate as the days lengthen and temperatures rise.
Seedlings not developing because of too much competition. If you have several seedlings to a pot or cell, they may be growing slowly (or not at all) because there’s not enough resources to go around. Cull the seedlings to one per growing unit by snipping the extras off at the soil line. Alternatively, transplant each seedling to its own larger container.
Seedlings not developing because of lack of nutrients. Seed-starting mixes are usually not fertile enough to support continued seedling growth. Transplant your seedlings into a nutrient-rich potting mix.
Seedlings not developing because they’ve outgrown their container. Even if your seedlings are in a rich growing medium and they each have their own pot, they may stall if they’ve grown too big for that container. Gently tip them out to inspect the roots; if there’s a crowded mass of roots (possibly taking on the shape of the container) it’s time to move to a bigger pot. Seed-starting mixes are usually not fertile enough to support continued seedling growth. Transplant your seedlings into a nutrient-rich potting mix.
Image credit: Sunflower seedlings by James A. Guilliam / Taxi / Getty Images