Light: Plants need light in sufficient quantity and intensity to grow. You will need supplemental lighting since few windows are enough. An ordinary shop light works great. Use 1 cool and 1 warm light bulb in the light fixture. Hang the lights 2-3 inches directly above the plants and raise the lights as the plants grow.
Air Circulation: Once they are up, seedlings need proper air circulation to prevent disease. Uncover during the day. A small fan might help move the air in the room if it is too damp. Make sure the fan doesn’t blow directly on the plants.
Temperature: Plants need warmth to germinate and cooler temperatures to grow in your house. This is critical! If it’s too warm the seedlings will become too leggy and worthless. Day temperatures should be 65-70° F and nighttime temps should be 55-60° F. This will help grow sturdy, compact plants.
Water: Seedlings like tepid water. Here is a good rule of thumb. Small plants like small particles of water. Larger plants like larger particles of water. Water with a fine mist from a squirt bottle or mist nozzle for small seedlings and use a “rain” style watering can spout for larger seedlings. Check with your finger to determine if watering is necessary, it’s the best indicator.
Food: Fertilize seedlings after they have their true leaves. The first set of leaves that grows is the “seed leaves.” They will drop off later. The next set of leaves are the true leaves. We recommend an all-purpose fertilizer such as 20-20-20. Excessive phosphorus at this point in development can lead to stretching of plants. After they have several sets of leaves or are beginning to bud, switch to a bloom booster fertilizer such as 10-50-10.
Damp-off: This is a soil born disease that manifests itself under the right conditions. Excessive heat, poor air circulation, insufficient light, and excessive humidity can all contribute. Damp-off shows up in several ways. The seedlings can wilt and rot almost right before your eyes, or the seeds may never germinate. This can be discouraging, to say the least!
Spindly Plants: Excessive heat or not enough light can make the seedlings grow spindly.
Remember, it is easier to prevent problems than fix them!