How To Start Plants From Seeds, According To An Expert

Starting vegetables and flowers from seeds is a fun way to start gardening long before it’s time to set out a single tomato plant or flower in your garden. It’s also a great way to stretch your gardening budget. “Seed starting saves money because plants cost several dollars each, but a packet of seeds is far less expensive,” says Gary Pilarchik of The Rusted Gardener and author of The Modern Homestead Garden and co-author of Growing an Edible Landscape. “Most seeds last for three years or longer if you store them in a zipper-top bag in a cool place, such as the fridge.”

Seed starting also allows you to get a jump on the season. By starting plants early indoors, you’ll have larger seedlings to transplant when conditions are right, which means an earlier harvest, says Pilarchik. Another plus is that you can grow unique varieties of plants that you won’t find at nurseries. Plus, it’s just plain satisfying to watch your plants grow–and it’s a mental health boost to get you through the last days of winter!

Some plants do better if seeded directly into the garden when conditions are right. That includes beans, carrots, radishes, turnips, and flowers such as nasturtiums and cosmos. But heat-loving crops, such as tomatoes, peppers, and eggplants, benefit from an early start indoors.

Here's what else you need to know to start seeds:

What You Need To Start Seeds Indoors

In addition to seeds, you’ll need a few basic items to get started:

• Seed-starting pots. “You don’t need to buy special pots. Water bottles, yogurt cups, and other food containers with holes punched in the bottom for drainage work fine,” says Pilarchik. However, if you prefer neat and tidy rows of seedlings, invest in seed-starting trays, which can be washed and reused for five to ten years. Avoid peat pots, which wick water away from the seedlings, aren’t reusable, and don’t biodegrade quickly.
• Seed tray or flat. This plastic tray is used to keep the pots together and for bottom-watering, which Pilarchik recommends.
• Potting soil. Any potting mix works fine; you don’t have need a special seed starting mix.
• Light source. “This is the most important piece of equipment,” says Pilarchik. “A window sill does not work because the intensity of the sun and the hours of sunlight are not sufficient to grow a healthy plant.” Choose a dedicated grow light or basic LED shop light with 5000 lumens or higher and a “daylight” Kelvin rating, which most closely mimics sunlight.

When Should I Start Seeds Indoors?

Depending on the type of plant, it can take a few weeks to a few months to grow a plant big enough to transplant into your garden. Timing is everything because plants started too soon will become spindly and unhealthy, while those started too late will delay your harvest, says Pilarchik.

 To figure out when it’s time to start seeds:

• Find your area’s last expected frost date; that gives you a good idea of when it will be safe, give or take, to set out seedlings. Your local coop extension service (find yours here) can give you an estimate.
• Count backwards from that date. If the seed packet says a crop should be started eight weeks before your last expected frost, and your last frost date is mid to late April, start these seeds indoors in mid to late February.  
• Or use a seed starting date calculator. If that all seems too complicated, use this handy calculator from Johnny’s Selected Seeds.

How To Plant Seeds Indoors

Fill your containers about three-quarters full with potting soil. Plant two seeds per pot, lightly pressing them into the soil about ¼-inch deep, or follow the instructions for depth on the seed packet, says Pilarchik. Label everything (no, you won’t remember what you planted where!).

Place the pots in a seed tray or flat. Set up the grow light or LED about 2 to 4 inches above the pots. Bottom water the seeds, following the steps below.

How To Water Seedlings

Watering from the bottom is less messy because you don’t splash out seeds and soil. Pour water into the seed tray and allowing the pots to absorb it, says Pilarchik. Wait until the planting medium is dark brown and fully saturated, then dump out excess water in the tray.

When the top of planting medium is light brown, it’s nearly time to water again. Let the surface of the pot dry for another day or two to prevent the growth of fungus and mold. Then fill the seed tray with water about one-quarter of the tray depth. Let the containers absorb the water for 30 minutes, then dump out excess. Do not allow the containers to stand in water.

How To Care for Seedlings

Keep the lights on for 14 to 16 hours per day. Most plants will take from 5 to 14 days to germinate. Water when needed by watching the surface color of the planting medium. As the seedlings grow, raise the light, maintaining the 2 to 4-inch gap above the plants. Remove competing seedlings with snips to prevent crowding.

About a week after they germinate, start feeding seedlings with a water-soluble fertilizer at one-quarter strength the recommended dose on the label. Add the fertilizer to the water when giving them a drink, feeding about twice a week to start, then about 3 to 4 times a week as the plants mature, says Pilarchik.

If it’s too soon to transplant outdoors but the seedlings are outgrowing their pots (you’ll see roots circling around the bottom of the pot or poking out the drain holes), transplant them into slightly larger containers, says Pilarchik. Go up about twice the size of the current pot.

When Can I Transplant Seedlings To My Garden?

Cold weather crops, such as lettuce and broccoli, can take a chill, but heat lovers such as tomatoes and eggplants need warm soil temperatures before they can be set out. “As a general rule, you want day time temperatures in the 60s and nights in the 50s for setting out cool weather crops, and day time temperatures in the 70s for setting out warm weather crops, such as tomatoes and eggplants,” says Pilarchik.

You also should get your plants “hardened off,” or acclimated, before planting them in the blazing hot sun, which will scorch their delicate foliage. Set them outside for 10 to 15 minutes in mild morning sun, then slowly increase the time they’re receiving direct sunlight over the course of a week or two, says Pilarchik. Set a timer on your phone so you don’t forget about them and let them fry! Once they’re hardened off, plant them in your garden, and wait for the harvest.