by Jorge Cervantes
Seedlings
During seedling growth, the root system grows rapidly while green aboveground growth is slow. Water and heat are critical at this point of development. The new, fragile root system is very small and requires a small but constant supply of water and warmth. Too much water will drown roots, often leading to root rot and damping-off (rotting at the soil line). Lack of water will cause the developing root system to dry up. As the seedlings mature, some will grow faster, stronger, and appear healthier in general. A little heat now will help nurture small seedlings to a strong start. Other seeds will sprout slowly and be weak and leggy. Most growers cull sickly, weak plants during the third to fifth week of growth, and focus attention on the remaining strong survivors.
Speed root growth by keeping the soil 2-5F warmer than the ambient air temperature. ideally the ambient air temperature should be 75F and the growing medium temperature 77-80F. Use heating cables or mat to raise the temperature of the growing medium.
If you have just a few seedlings, you may want to save weak, slow-growing plants. Baby such small plants along and let them grow longer until they catch up with the others before moving them into the next stage of growth.
Seedlings need at least 16 hours of light daily. Many growers give seedlings 18-24 hours of light per day so they will grow as fast as possible. Seedlings that receive 16 hours of light and 8 hours of darkness tend t grow more female plants.
Seedlings require less intense light now and grow well under fluorescent tubes or compact fluorescent lamps (CFLs) for the first two to three weeks. Keep fluorescent lamps two to six inches above seedlings and CFLs 12-18 inches above foliage.
Metal halide or HP sodium HID lights can be used to grow seedlings. Growers prefer metal halides because the color spectrum of HP sodium lamps tends to make seedlings stretch between branch internodes. Keep HIDs three to four feet (90-120cm) above seedlings for best growth.
The seedling stage is over when rapid foliage growth starts. Rapid growth above ground is the beginning of the vegetative growth stage. Plants need more room to grow; transplanting into a larger container hastens development.