All-purpose potting mix has composted bark, peat moss or peat humus added to loamy soil. Gardeners usually add ingredients to customize mixes - like extra peat moss, sand, perlite, etc.

Ready-to-use premium mix contains similar material but in different proportions. More bark and peat and less soil make it lighter. Perlite and vermiculite give it better drainage and aeration. Many contain a wetting agent for uniform water distribution. Some are billed as "soiless mixes" - these can be the safest to use because they will not harbor fungi or bacteria, but you must fertilize because there are NO soil nutrients in them!

Professional mix has the same materials as the premium types but is more finely processed. It works well for starting seeds or transplanting delicate seedlings.

Plant-specific mixes are used when you have a certain plant in mind with special requirements. Orchid, African violet and Cactus are just a few of the special mixes available.

Light

All plants need light to grow, but young seedlings will benefit from more intense light than adult plants. You can raise seedlings on a shelf or windowsill in a sunny, south-facing window with good results. You do have to remember to keep rotating the plants in the flats a quarter turn every day or seedlings will keep growing toward the window and get lopsided.

You'll have healthier, less spindly plants if you can provide some supplemental light. Although they provide excellent lighting for plants, expensive, full-spectrum growth lights aren't necessary.  Ordinary fluorescent tubes will work just fine if you use one warm-white and one cool-white bulb. Hang a two-bulb shop light fixture with a reflective hood over the bulbs. The fixtures and bulbs can both be bought inexpensively at home-supply stores.  The height must be adjustable to keep the lights 2 inches or less above the tops of the plants at all times.

Plants need periods of darkness as much as they need light to grow and develop. For young seedlings, a cycle of 18 hours light and six hours dark is ideal. Use an inexpensive timer set to come on at or before sunrise, and off at or after sunset.

Get creative - you don't have to buy those plastic trays with the domed lids and the inserts for them. Plastic or metal  containers with clear

To make sure your tomato plants are well anchored, you should bury their stems up to the lowest leaves. Pastor Mustard plants his tomatoes the right way from the start - odd looking, but effective. Use deep containers, such as frozen concentrate juice or soup cans.  Poke drainage holes in the bottom of a clean can. Then fill the can about half full of potting soil and add a seed (see illustration 1). As the plant grows, keep adding more and more potting soil to encourage root development  (see illustrations 2 and 3). Finally, when it's time to transplant, simply take off the bottoms of the cans and push out the plants.

Peppers also benefit from deep rooting, but do not require the depths that tomatoes do. Usually, just planting them slightly deeper should do the trick.

Seeds store enough nutrients to germinate and grow cotyledons - leaf-like structures also called seed leaves, that are different from the true leaves the plants have in their adult lives. 

After one set of true leaves emerges, fertilize  seedlings twice a week with a balanced, water-soluble fertilizer at half the strength indicated on the label. If you've used soil in your medium, it will provide many of the nutrients the seedlings need, so you only need to fertilize every 10 days or so. Using an oscillating fan on medium setting helps simulate the wind, making the plants stronger and stockier.

Finally, after several weeks of nurturing your seedlings, you should have healthy, stocky plants with a good foundation to thrive and produce. But they need to be toughened up to deal with the outdoor environment. About 2 weeks before it's time to plant in the garden, decrease the plants' water and stop fertilizing. 

A slightly lower temperature is a good idea, too. This slows growth and makes foliage less succulent. Then spend another week hardening the plants to the outdoors. Start with a few hours exposure to shade each day, increasing to full sun over the course of a week.

Fortunately, there are lots of places around the home that can provide a little extra warmth.  Gentle bottom heat under the flat is preferable because it's applied directly to the medium, where the seeds are. Try the top of a refrigerator, water heater or furnace. Spots near radiators and heating registers are fine, but not too near - too much heat can be as detrimental as cold. And check flats in warmer spots often because they may dry out quickly. 

It's easier to use an electric heat mat specially made for putting under flats of seedlings. It works much like a regular heating pad. Heating cables are another option. Since they're flexible and come in various lengths, and can be customized to fit the space.

Both types of heating come either with or without thermostats to control the temperature. As soon as the seedling shoots emerge and stand up straight, they prefer cooler temperatures, so you can remove artificial heat and concentrate on putting the flats in the best available light conditions. This fact also helps you economize on buying heat mats or cables. 

Since you start different types of seeds at different times, the early ones are through with their bottom heat in time for the next batch. For those that require more warmth while growing, try using an old aquarium! It doesn't matter if it's leaky.

Moisture is required for seed germination. Most seeds remain dormant until they are in a warm environment where they can soak up water. Keep seeds and young seedlings constantly moist but not wet; otherwise  they could rot or their pots might get moldy. It's also best to avoid a sudden gush of water that could displace seeds or knock over tiny seedlings. One way of doing this is to use a fine-nozzle sprayer to gently mist seedlings.

Bottom watering works even better. This is where using peat pots in a plastic tray comes in handy. Both peat pots and peat-based seed-starting mix are highly absorbent. Pour water into the tray around the pots and let it wick up, moistening the medium indirectly. You can also leave one pot empty and water all the plants through there. This ensures even bottom watering, cutting down on the possibility of getting afflicted with mold.

Don't leave excess water standing around the bases of the pots. Try putting small amounts of water in at a time, letting that soak up and then adding a little

Transplant seedlings with a metal fingernail file. The pointed end will lift out even the smallest seedling while the curved end separates seedlings that are growing in clumps. Look in kitchen drawers for tools you can use. You may even find some that prove more useful in the yard and garden than in your kitchen. Or, use bamboo shish kabob skewers or Japanese chopsticks. They're useful for prying the seedlings out of the starting mix when transplanting. The thin, pointed tip works well for teasing roots apart on seedlings which have grown together.

Hold seedlings by their first leaves rather than the stems. At this tender stage, the stems can be easily bruised or broken. Using the the  leaf from tearing away from the plant. Also remember to replant each seedling as you move it. Even a short time out of the soil will dry the roots and slow down the re-establishment of the young plant. After they've been watered in, some of the starts fall over and lay on the soil. The skewer makes a good tool for carefully lifting each plant and holding it upright. Then, a second skewer comes in handy for gently firming the soil to help the seedling stand up until the roots take hold.

In late spring, cutworms can devastate vegetable and flower gardens by mowing down tender seedlings at ground level. One way of protecting plants is with cutworm collars. Recycle honey, peanut butter tubs, and yogurt containers for this purpose. In the event of a cold snap, the collar also can double as a mini greenhouse by popping on the lid.

You could also make cutworm collars from old lawn edging, cutting strips, rolling them into a circle, and stapling the overlapping edges. As you slip a collar around a plant, press it into the soil so at least an inch of it is buried and at least 2 inches are above soil level. This way critters can't crawl under or over the barrier.

Cutworms are hairless caterpillar-like critters that treat your garden like a midnight buffet - munching off the young seedling at or just below the soil surface.  Don't forget to weed, feed and water your seedlings in the garden! 

If you've made this far, you're on your way!