When the seedlings look robust and are about 4 inches high, you can transplant them into the garden. When you are ready to plant them outdoors, be sure the forecast is for mild weather. Rainy or overcast days are best for transplanting.
Hardening Off Seedlings
Hardening off is a method of toughening up seedlings started indoors so they can survive outside. Do this by spending a week or two (depending on the weather) gradually getting them used to the extremes of outdoor temperatures.
Begin a week before setting them outside by drying them up. Don’t let them wilt, but water them less frequently; a little water stress toughens them and prepares them for outdoor conditions.
When you’re ready to harden them off, place the seedlings in a sheltered spot but out of direct sunlight for three or four days, bringing them inside in the evening. Then place them in a spot with direct morning sun for another three or four days, leaving them out if the nights aren’t too cold. If the weather is cold or harsh, spend two weeks hardening them off. Be sure to keep them watered—they dry out quickly.
After this period of acclimation, they are ready to go into the ground.
Seedlings in Peat Pellets
Before transplanting seedlings growing in peat pellets, soak the bottoms of the pellet, then pull apart the bottom third of the pellet, leaving the top intact.
Seedlings in Peat Pots
Seedlings in peat pots are planted pot and all. Tear off the top edge of the pot just below the soil line before planting it. Bury the pot completely. If a peat-pot edge protrudes from the soil, it will wick moisture away from the rootball.
Seedlings in Flats
You can free seedlings that have become intertwined in a flat by cleanly slicing them apart with a sharp knife. Some gardeners prefer to grasp the rootball with their fingers and gently pull the seedling away from the others, keeping as many of the roots intact as possible.
Seedlings in Pockets
To transplant seedlings growing in pockets in a commercial “six-pack”, use your thumbs to push up the bottom of the pocket and gently lift out each rootball, one at a time.
Planting the Seedlings
Place small seedlings in a furrow made with a hoe. Place a few seedlings at a time in the furrow, then push soil over their roots; the roots dry out quickly, so don’t let them stay exposed too long.
Plant larger transplants in a hole made by stabbing with a trowel. Set the transplant so it is at the same level as it was in the flat and press the soil back around the root ball. Water the seedlings in well, even if the soil is damp. This “puddling in” helps to settle the soil around their roots.
Don’t let the seedlings dry out. Wind can be as devastating to a seedling as heat and sun. If threatened, arrange a makeshift wind screen of burlap, lattice, or old sheets. In cold regions keep a roll of row cover handy. You can tent it over tender plants if low temperatures are expected. See for more information.