The Golden Rule is to never handle plants by their stems, which bruise easily, but by their first seed leaves. Take care not to damage the delicate roots. To transplant, just ease the seedling out of the soil with a sharpened pencil. Use the pencil to make a hole, and then neatly place the roots in the hole. Gently press the soil into contact with the seedling while still holding the leaves. Start feeding with a diluted (half strength) all purpose fertilizer (20-20-20) a couple of weeks after transplanting. You can also use a “starter” solution when transplanting.
The final step before planting outside is to harden off young plants. The idea is to gradually get the seedlings accustomed to the harsher conditions outside. Allow approximately 10 days to do this. The coldest temperature most plants can handle is 50° F.
Start by putting the trays in a sheltered, sunny area outdoors for a couple of hours per day during the warmest hours of the day (usually between 1:00p.m. and 4:00p.m.). Slowly increase the amount of time, so when the fear of frost is gone (usually around June 1st) the plants are fully conditioned to being outside.
You can also use a cold frame to harden off your plants. Use glass or plastic to cover a frame.
Another great product for hardening off plants is floating row cloth. It is a thin felt-like product that you can cover your plants with. It protects them like a blanket, yet allows them to breath.
Here is a great trick I learned from a customer: Take anything on wheels, a truck, little red wagons, snow machine trailer, cart, whatever, and roll your seedlings outside. Store them in a garage at night and roll them out during the day. It works great. If you don’t have a garage, just carry them into the house for the night.