In winter, garden seed catalogs begin arriving by the dozens and we start thinking about starting seeds for flower and vegetable plants.

Growing your own transplants can be rewarding if you follow a few guidelines.

Seeds can be started in a wide variety of containers.

Many types of plastic flats and packs are available in garden centers.

You grow each plant in a cell and don’t have to remove the plant until you transplant it into your garden.

Other popular containers are peat pots, which are made from peat or wastepaper fibers.

The plant and pot are both transplanted into the soil.

Other types of pots that work well are wood flats, fiber trays, plastic trays and clay or plastic pots.

You can use a soil or a commercial potting mix to start the seeds.

The most important thing to keep in mind is that seeds prefer a loose, well-drained, fine textured medium in which to grow.

Some plant diseases are carried in the soil, so be sure that whatever medium you use it is sterile.

Choosing your seeds is often the most difficult part of starting seeds indoors.

However, once your seeds arrive you need to plan carefully when to sow them.

Plants grow at different rates and have different tolerances for cool weather.

Some plants are ready as soon as four weeks after sowing; others may take as long as 14 weeks.

Check the seed package for the number of weeks before the last frost date.

For the Lehigh Valley, the average last spring frost date is around April 26, but it’s safer to wait until early May (around May 6-10) for tender plants, as there’s still a chance of frost in early May, with a 90 percent chance of no frost by late May.

Fill the seeding container to within three-quarters inch from the top with moist soil.

Whatever container you choose, be sure it has adequate drainage for excess water.

If you are planting one kind of seed in the container, you can broadcast the seed onto the soil.

If planting more than one kind of seed in the same container, use a narrow board to make shallow rows in the container approximately one to two inches apart.

This will help you keep the different types of seed separated.

If using individual pots to plant your seeds, place two seeds in each pot.

After the plant begins to grow, thin to one plant per pot.

Cover the seeds according to the directions on the seed packet.

Larger seeds such as cucumber and melons will need to be planted deeper than small seeds such as tomato or marigold.

A general rule of thumb is to cover the seeds with soil twice the diameter of the seed.

Cover your seeding containers with a plastic bag to keep in moisture.

For larger containers, cover with a piece of window glass.

You should not have to water until after the seeds have germinated.

Place the seeds in a warm location.

The best temperatures for germinating are between 65 and 75 degrees, although some plants prefer cooler temperatures.

As soon as the plants germinate, move to bright light and remove the plastic or glass covering.

Water the seedlings when dry and add fertilizer to help them grow.

Don’t forget to harden off the plants before transplanting outside in your garden.

“Growing Green” is contributed by Diane Dorn, Lehigh County Extension Office Staff, and Master Gardeners. Information: Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-813-6613