Plant or transplant seedling by selecting the best date for the specific plant depending on its hardiness, hardening off the seedling, using well-drained soil and adding mulch. Immediately add a light starter fertilizer to the soil to encourage root growth.
To harden off or acclimatize a seedling to the outdoors before planting it, stop fertilizing it, and reduce watering 10 days prior to planting. Place the seedling outdoors for a few hours a day, bringing it in at night. Place it in the shade for the first few days, and then move it to a sunny spot in the mornings. After day seven, allow the plant to stay outdoors all night as long as the temperature is above 50 degrees Fahrenheit.
After 10 days, test the soil in the new planting spot or garden bed, making sure it's moist but not damp. It also needs to be well-drained and aerated to prevent root rot. Mix a generous amount of manure or compost into the soil before digging a hole big enough to fit the seedling's root ball. Gently slide the plant from its tray, and plant it in the hole.
Immediately water the seedling and give it a diluted phosphorus-heavy 15-30-15 ratio starter fertilizer. Spread mulch around the plant to help keep the soil warm and moist.