14 Tips For Growing Healthy Seedlings

Ensure that your plants are organic from start to finish by starting your own seeds.

April 13, 2017
how to start seedlings
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When you start your own seeds, you can be sure that your plants have been raised organically from first to last. And by sprouting and nursing your own seedlings, you don't have to wait for warm weather to get your hands dirty. Best of all, it's easy and fun—but when seedlings die, it can be extremely frustrating. Here's what you need to know to keep them alive and healthy.

(Whether you're starting your first garden or switching to organic, Rodale’s Basic Organic Gardening has all the answers and advice you need—get your copy today!)

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1. Pick The Right Plants

Some plants lend themselves to home germination better than others. Surefire vegetables include basil, broccoli, brussels sprouts, cabbage, cauliflower, chives, leekslettuce, onions, peppers, and tomatoes. Some reliable annual flowers are alyssum, cosmos, marigolds, and zinnias. Perennials include Shasta daisies, columbines, and hollyhocks.

2. Plant At The Right Time

To calculate when to sow your seeds, go to our seed-starting chart, print it out and then fill in the blanks. Then you will have a planting plan you can follow through the season.

plant seedlings at the right time
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3. Choose The Right Containers

Biodegradable pots work great, but you can also reuse last year's nursery flats or even plastic clamshell containers like the ones berries and salad greens come in. Otherwise, any container 2 or 3 inches deep will do. Punch holes for drainage into the bottom of containers and set them into trays. Protect against plant disease by thoroughly cleaning all used containers: Wash them in hot, soapy water, and rinse with a dilute solution of household bleach and water. If you want a less-irritating substitute for the bleach, use distilled white vinegar.

Related: 26 Plants You Should Always Grow Side-By-Side

4. Choose Good Soil

You can buy bags of seed-starter mix or you can make your own seed-starting mix by blending equal parts of perlite, vermiculite, and peat. Add 1/4 teaspoon of lime to each gallon of mix to neutralize the acidity of the peat. You'll eventually want to repot most of your seedlings into larger containers before setting them into the garden. But lettuce, melons, and cucumbers are finicky about being transplanted and should go directly from the original containers into the garden. When starting these fussier plants, always add two parts well-aged, screened compost to your mix to give them a healthy beginning.

right pots for seedlings
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5. Sow Carefully

Moisten your medium in the containers before sowing the seeds. Next, drop seeds onto the surface of the mix, spacing them as evenly as possible. Cover the seeds to a depth about three times the thickness of the seeds. Some seeds, such as ageratum, alyssum, impatiens, petunias, and snapdragons, should not be covered at all because they need light in order to germinate.

6. Top Off The Pots

Lightly sprinkle milled sphagnum moss, a natural fungicide, over everything to protect against damping-off, a fungal disease that rots seeds and seedlings. In the case of seeds that need light to germinate, sprinkle the moss first and then drop the seeds onto the moss.

Related: A Simple Step-By-Step Guide To Starting Your Own Seeds

keep seedlings warm
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7. Keep Them Warm

Cover the flats with plastic wrap or glass to keep the environment humid and place them near a heat vent or on a heat mat made especially for seed starting. Most seeds germinate well at about 70 degrees.

8. Keep Them Damp

Mist with a spray bottle or set the trays into water so the mix wicks up the moisture from below.

tips for growing seedlings
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9. Keep Them Well-Lit

At the first signs of sprouting, uncover and move the containers to a bright spot—a sunny window, or beneath a couple of ordinary fluorescent shop lights (4-footers with two 40-watt bulbs). The lights are worthwhile, especially if you live in the North. They provide a steady source of high-intensity light. Short days restrict window light, and your seedlings need 12 to 16 hours of light a day. Suspend the lights just 2 inches above the plants and gradually raise them as the seedlings mature. If plants have to stretch or lean toward the light, they can become weak and spindly. To turn the lights on and off at the same time each day, hook them up to an electric timer.

Related: Everything You Need To Know About Starting Seeds Indoors

10. Then Cool Them Down

Seedlings don't have to stay as warm as germinating seeds. Move them away from radiators and air vents, or off the heating mat, as soon they have germinated.

growing seedlings
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11. Fertilize

If you're using a soil mix without compost, begin to fertilize your seedlings as soon as they get their first true leaves. (These leaves emerge after the little, round cotyledon leaves.) Water with a half-strength solution of liquid fish/seaweed fertilizer every week or two. Use either a spray bottle or add the fertilizer to the water you set the trays in if you're using the wick-up method described above.

12. Give Them Space

If the seedlings outgrow their containers or crowd one another, repot them into larger containers filled with a mix that includes compost. Extract the seedlings with a narrow fork or flat stick, and handle by their leaves and roots to avoid damaging the fragile stems. Tuck the seedlings gently into the new pots, and water them to settle the roots.

Related: 10 Plants You Need To Grow If You're Suffering From Depression, Stress, Or Anxiety 

choose right soil for seedlings
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13. Pet Them

Lightly ruffling seedlings once or twice a day with your hand or a piece of cardboard helps them to grow stocky and strong. Or, set up a small fan to gently, continuously blow on your seedlings.

Related: 5 Biggest Seed-Starting Mistakes You're Making

14. Toughen Them Up

About 1 week before the plants are to go outside, start acclimating them to the harsh conditions of the big world. Gardeners call this hardening off. On a warm spring day move the containers to a shaded, protected place, such as a porch, for a few hours. Each day—unless the weather is horrible—gradually increase the plants exposure to sun and breeze. At the end of the week leave them out overnight; then transplant them into the garden.