Now’s the time to get those seeds started and under lights

Now is prime time to get busy if you’re getting a jump on the season (and saving money) by starting some of your own flowers and vegetables inside from seed.

The way to know when to start what is to count backwards from when you’d like to have planting-sized plants ready.

Decide on that date and count backwards eight to 12 weeks to determine a plant’s seed-start date (one to two weeks for the seed to germinate, six to eight weeks of growing time, and another week to 10 days to gradually acclimate the seedlings outside before planting).

Varieties that can take frost and slow-growers that need a long lead time can be started as early as late January through mid-February. Examples: veggies such as broccoli, cabbage, kale, leek, onion, lettuce, parsley, and cauliflower, and flowers such as pansies, violas, snapdragons, and most perennials.

The bulk of flowers and vegetables, though, can’t go outside until after all danger of frost. Historically, that’s been around mid-May for most of the Harrisburg area, although our average last-frost dates have been creeping steadily earlier. The average over the last 23 years is actually April 11, according to National Weather Service data from Harrisburg International Airport, while last spring the last 32-degree night was March 25, 2024. (Spring dates are later in outlying areas and areas north of Harrisburg.)

• See the NWS chart on the Harrisburg area’s first and last frost dates for each year since 2000

Depending on your location, frost-risk tolerance, and target planting dates, early to mid-March is prime indoor seed-starting time for warm-weather veggies such as tomatoes, peppers, eggplants, basil, cucumbers, and melons, and summer annuals such as marigolds, zinnias, petunias, impatiens, ageratum, celosia, gloriosa daisy, nicotiana, and vinca.

• See George’s plant-by-plant list of when and how to plant each type of edible

Seed-starting isn’t as hard as you might think. You don’t need a greenhouse, a fancy store-bought contraption, or even special “grow lights” to start plants from seed.

Here’s an eight-step how-to, involving recycled and inexpensive materials:

1.) Gather some used plastic containers, such as margarine tubs, cut-off milk containers, or yogurt cups. Clean them well, and drill or poke eight to 10 small holes in the bottom for drainage.

Fill the containers two-thirds full with vermiculite, which is a light, fluffy, water-holding mineral sold in bags in garden centers.

2.) Scatter seeds over the surface of the vermiculite. Then cover with a light layer of more vermiculite, according to recommended depths listed on each seed packet. (Some varieties should be pressed into the surface, not covered.)

Label the containers so you know what’s what.

3.) Wet the vermiculite. Place your seeded containers on a tray (either store-bought plastic trays or cleaned, recycled foam meat trays are fine), and gently sprinkle the surface with water. Add enough water so the vermiculite is saturated and draining out the bottom.

An alternate technique that’s less disruptive to seed depth is setting the vermiculite containers in a tray with water until the vermiculite has soaked up enough to become damp at the surface.

4.) Cover and wait for sprouting. Keep moisture in by lightly covering the containers with plastic wrap. Set the trays near a sunny window at room temperature, and watch for the seeds to sprout.

Seed packets will tell if a variety needs warmer temperatures to sprout. Those can be set on top of an appliance (water heater or refrigerator) or on top of a heat mat (available from garden centers or through garden catalogs).

If the vermiculite is drying before the seeds are up, add water to the tray so the vermiculite can soak it up and become damp at the surface again.

5.) Transplant the seedlings. Once the first set of leaves have unfurled, use a pencil or similar pointy object to transplant seedlings into individual pots or cells. (Label these, too.)

Recycled plastic four-packs and six-packs from past purchases are fine, so long as you’ve cleaned them and soaked them in a 10-percent bleach solution for 15 minutes to head off disease.

For bigger transplants such as tomatoes, pepper or a specimen annual flower, use recycled four-inch pots – also cleaned and bleach-sterilized.

Fill these pots and six-packs with slightly pre-moistened potting mix. Buy fresh, quality, light-weight mix – not used or cheap mixes or garden soil.

Set the seedling pots/packs in trays (with no holes), and gently water.

(Note: Some people skip the two-step process and seed directly into the pots and packs, using scissors to snip off excess seedlings.)

6.) Set the trays under lights. Even sunny windows aren’t bright enough to yield stocky seedlings. You’ll get better results by investing in tubular fluorescent or LED workshop lights and hanging them on chains so you can keep the lights just two or three inches above the plants as they grow.

Lights should run 14 to 16 hours per day, then go dark overnight to mimic summer outdoor lighting.

Cool rooms at temperatures around 55 to 60 degrees are perfect.

If you’re willing to invest more money, higher-performing T5 fluorescent lights are available that are brighter than, more efficient than, and equipped with a better light-spectrum profile than the basic tubes from the home center.

• Read more on the right light for seedlings

7.) Water and fertilize. Keep the seedlings damp by “bottom-watering.” This means adding water to the tray and allowing the potting mix to soak it up instead of watering over the top.

Add only enough water to the trays so that the plants soak it all up in 15 or 20 minutes. Pour out excess after that time and water less next time.

Add quarter- to half-strength fertilizer to the water every watering or two. Go with a balanced-formula fertilizer, something along the lines of 10-10-10 or 20-20-20 on the label.

8.) “Hardening off.” Once plants have reached transplantable size, give them increasing light and wind exposure each day over a seven- to 10-day period to get the tender seedlings used to the harsher outdoor conditions.

Set them in shade for a couple of hours the first day, then gradually give more light and more time out until they’re outside round the clock for a couple of days before planting.