Drum roll, please: We are six weeks away from the first day of spring. Recent warm Colorado days have previewed the changing seasons, but we know that along the Front Range, extreme cold weather events can occur in April or May.

No matter the weather, now it is time to get your indoor seed supplies ready to go.

Below are my most reliable seed-starting tips. Have there been years when germination has been spotty or not at all? Sure, errors happen, or the operator (me) uses seeds that a too old, which is frustrating because time is lost and a do-over is required.

Test your seed viability by scattering several seeds on a damp paper towel, then fold the towel and place in a sealed plastic bag near a sunny window. If less than half the seeds have sprouted after 10 days, buy new seeds. Or do as I do: Trek to your favorite garden center, purchase new seeds every year, or every other year, and rest assured that germination will be good to very good.

Timing

The most important seed-growing information is right on the seed packet. The correct time to directly seed indoors varies by plant type, generally ranging from two weeks to 16 weeks prior to the final spring frost (which is around May 10 along the Front Range). This time frame does not include the days to weeks the seed needs to germinate or emerge from the soil.

This indoor growing time also does not include the week it takes to “harden off,” or toughen up the transplant to outdoor growing conditions. For instance, if the seed packet says tomatoes should be started five to seven weeks prior to the last frost date and seed emergence is anywhere from seven to 21 days, add seven hardening-off days and the best time to directly seed this tomato variety indoors is mid-March.

If the outdoor soil is too wet, or if there is snow on the ground around planting time, then the transplant will need to remain indoors and well cared for with water and fertilizer. Weather in Colorado has taught many a gardener all about patience when getting the spring garden planted.

Indoor seeding tips

1. In addition to store-bought seed starting trays and kits, don’t overlook items from home like yogurt cups, egg cartons and plastic produce packages to start seeds. Be sure to clean and sterilize all previously used containers with soap and hot water, then wipe them with diluted hydrogen peroxide or bleach and rinse well prior to use.

Biodegradable pots are popular, but in Colorado outdoor soils are generally too dry to be planted with the new transplant. Remove the plant first from the biodegradable container before planting for the best growth outcome.

2. Poke or drill drainage holes in all containers if not already done. Then use a label system for each plant or tray with purchased plant markers or cut up some of the plastic tubs or lids and make your own.

3. Always use brand-new potting soil designated for indoor seeding. If the potting soil bag label says there is added fertilizer, then take care not to add too much more fertilizer while the seeds are germinating and during the plant’s early growth.

4. Moist soil is easier to work with before adding seeds. Either add water to the bag of soil if it is dry or fill the planting container and moisten with water prior to seeding.

5. Fill containers with potting soil, poke holes to drop the seed in using a sterilized chopstick or similar tool. The seed packet tells how deep the seed goes in the soil, or if they can rest on top of the soil only needing light to germinate.

6. For vegetables: Drop two seeds in each hole, and later, when the stronger one is up and growing, cut off the weaker one to avoid damaging nearby roots. Cover the seed tray with clear plastic or a dome until the seeds emerge. The tray does not have to be under lights or near a window during this stage.

7. Using a bottom heat mat under the seed tray is one of the best investments for starting seeds since they warm up the soil which can speed up seed germination. Some gardeners find warmth for the seed trays when they are placed on top of refrigerators or other appliances. If using a seed mat, be sure to plug the electrical cord directly into the wall socket and not into the light timer, since the heat mat should always be on until the plants are up and growing well on their own.

8. Remove the plastic wrap or cover domes immediately after germination and then place the tray(s) under grow lights. Growing results are generally more reliable with either LED or fluorescent lighting than solely depending on a sunny window.

Place the newly emerged seeds close, a few inches undernearth the grow lights. Keep an eye on the foliage and move the lights up if plants begin to brown at the leaf tips.

Use a timer and keep the lights on for 14-16 hours each day, off for the remainder of the day.

9. Place a small fan near, not necessarily directly over, the seedling trays. Keep it on 24/7 at the lowest setting until the plants are up and growing well, usually after two or three weeks. Air circulation is the best defense against seedlings suddenly collapsing and dying (called damping off disease).

Seedlings prefer to be watered with room temperature water so fill a clean watering can with water and leave it close by. Use half to quarter strength liquid fertilizer for watering every other time.

10. To prevent damping off, avoid overwatering and never let the trays or containers stand in water for any length of time. Water lapses can lead to plant death, too.

My go-to for watering is using a capillary mat under the seed tray. They look and feel like felt and are very absorbent. They are sold in rolls or sheets at garden centers and online. Cut the mat to the size of your tray. Mats are reusable from year to year and machine washable on the gentle cycle (air dry). Simply pour some room temperature water over the mat about every other day or as needed and leave it to the soil and seeds to soak up the water they need.

11. Transplants can be potted up to a larger container as they grow. Look for at least three sets of leaves on the plant. Use a dull knife or spoon to carefully loosen the soil edges in the smaller container and move the entire root ball with soil to the next size container, usually from a 2-inch to a 3- or 4-inch size. Moist soil makes for easier potting up.

Now is the perfect time to gather friends together to exchange garden seeds for the upcoming outdoor garden season. Make it a real seed party by serving food and drinks. Then talk about gardening and the good times ahead.

Resources

• More in-depth primers including videos on seeding indoors, outdoors plus seed saving can be found at https://growgive.extension.colostate.edu/grow/general-gardening-info/seed-starting-and-seed-saving/

• The Simple Trials of Seed Germination https://csuhort.blogspot.com/2019/02/the-simple-trials-of-seed-germination.html

Betty Cahill writes and speaks about gardening in the Rocky Mountain Region.