Plan early to start your transplant seedlings. This includes ordering or purchasing the seeds as early as possible. Typically plants will require 6 - 8 weeks of indoor growth before being set out in the garden.
Have all other supplies on hand as well. The following are the basics:
Transplant containers (paper/styrofoam cups)
Labels & Pen for marking
Trays to hold containers/cups (old cookie sheets, baking pans, dish pans work well)
Moisture cover to keep moisture in during germination (plastic food wrap or glass)
Preparing to Plant
Prepare the growing mixture by dampening the mixture at a ratio of approximately 8:1. This can easily be done in the original plastic bag. The mixture should be uniformly damp.
Make sure containers and tools are clean so as to not transfer any harmful organisms to the seedlings. Cleaning can be done by using soapy water and soaking in bleach water.
Planting the seeds
Fill seedling containers to within one-quarter inch (1/4") of the top with the prepared soil.
Level and flatten the soil. (If you are using peat pots, be sure to wet them first as they will draw the moisture from the soil leaving the seed dry.)
Plant 3-4 seeds per hole (if using a flat) or per container if using individual pots. Planting more seeds than needed allows you to select the best seedling - and not all seed will germinate.
Cover the seeds by pushing dirt from the side of the hole to cover the seed. Only cover to a depth of 1-2 times the thickness of the seed.
Lightly spray the surface with water from a clean spray bottle.
Label the pots (or flats) unless you've only planted one type of seed.
Covering the Containers
Cover the pots (or flat) with clear plastic wrap, clear glass or acrylic. (Discarded bags from dry cleaning also make serviceable covers, however, make sure the plastic does not touch the pots by using some sticks to hold the cover up.)
Light & Heat
If you don't have a soil heating mat, seedlings can be kept warm in the house - assuming you have the space. On top of the refrigerator is a good place and keep the moisture in and the top of the refrigerator clean by placing layers of old newspaper under the seedling pots.
Other warm places in the home are near the furnace, water heater - however, do not place the pots (or trays) on top or under any heat source - and DO NOT use any paper or flammable material near a heat source.
Do not place seedling containers in direct sunlight. Having the plastic wrap, glass, etc. on top will trap the heat and be fatal for most seeds.
Pots and containers should be checked daily for dryness, mold and growth. To water seedlings water from the bottom, do not pour water on top. To water from the bottom, place the containers in a dish/tray of lukewarm water. Leave there until the top of the soil appears moist. Remove from water tray and replace plastic cover. While condensation on the plastic is expected, if you begin to see mold, remove the cover a couple of times a day for about fifteen (15) minutes.
Once seedlings appear, remove the cover and move to a light source. This can be a sunny south window, greenhouse, fluorescent lights. Seedlings should be turned every few days if in a window for even growth. Care should be used with fluorescent lights to avoid curled leaves.
Do not allow seedlings to dry out. Use the bottom watering discussed above to keep them moist. Overhead watering is usually safe once the seedings have developed a root system and have their second set of leaves. If you have your containers in a tray, do not allow the plants to sit in water this may cause root rot.
After a few weeks, allow the soil to dry out some (1/2 - 3/4 inch) before watering. The helps prepare them for the outdoor garden. When to water is not critical as long as the seedlings are not wet through the evening.
When watering use room temperature water.
If possible use an organic fertilizer. Also, more frequent but less concentrated applications are better. This can be accomplished by doubling the dilution recommended on the fertilizer container.
Thinning - Transplanting
When thinning remember the more plants the more tangled the roots. Thin the seedlings leaving only the strongest looking plant.
Seedlings should have an adjustment period before moving to the garden. This procedure should be started about two weeks before actual transplanting into the garden begins.
This can be accomplished by setting the plants outside in a sunny area for about two hours (middle of the day) and then replacing them in their previous environment. Next day leave them out for 3-4 hours, next day leave them out all day and bring them back in. On the fourth day take them out and leave them out for the rest of the two weeks.
During this time monitor their water needs.
Once the seedlings have been completed their adjustment period, they are ready to be transplanted.