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How to Start Seeds
A comprehensive guide to growing vegetables and flowers from seed
There are many ways to start seeds, but a seed-starting system, such as the GrowEase Seed Starting Kit ensures good results.
Keep it Simple
Growing plants from seed is a great way to start gardening earlier in the season. With the right light and some simple equipment, it’s easy to grow from seed to harvest.
Because each plant has unique seed-starting requirements, it helps to start small by growing just a few varieties. Some seeds — such as tomatoes and marigolds — are especially easy to start indoors. Other good choices for beginners are basil, zinnia, coleus, nasturtium and cosmos. If you’re a beginner, choose those first, and then move on to more fussy seeds, such as petunias.
Marigold growing among vegetables
Seven Steps, from Seed to Garden
Get the timing right
The goal with seed starting is to have your seedlings ready to go outside when the weather is favorable. Start by looking at the seed packet, which should tell you when to start seeds inside. Usually, it will say something like, “Plant inside six to eight weeks before last frost.”
Some types of vegetables, such as beans and squash, are best started outdoors. There is little benefit to growing them indoors because they germinate and grow quickly. Some flowers, such as poppies, are best planted outdoors, too. These seeds are usually marked “direct sow”.
Find the right containers
Prepare the potting soil
Choose potting soil that’s made for growing seedlings. Do not use soil from your garden or re-use potting soil from your houseplants. Start with a fresh, sterile mix that will ensure healthy, disease-free seedlings.
Before filling your containers, use a bucket or tub to moisten the planting mix. The goal is to get it moist but not sopping wet; crumbly, not gloppy. Fill the containers and pack the soil firmly to eliminate gaps.
Remember that most mixes contain few, if any, nutrients, so you’ll need to feed the seedlings with liquid fertilizer a few weeks after they germinate, and continue until you transplant them into the garden.
Check the seed packet to see how deep you should plant your seeds. Some of the small ones can be sprinkled right on the soil surface. Larger seeds will need to be buried. For insurance, I plant two seeds per cell (or pot). If both seeds germinate, I snip one and let the other grow. It’s helpful to make a couple divots in each pot to accommodate the seeds. After you’ve dropped a seed in each divot, you can go back and cover the seeds.
Moisten the newly planted seeds with a mister or a small watering can. To speed germination, cover the pots with plastic wrap or a plastic dome that fits over the seed-starting tray. This helps keep the seeds moist before they germinate. When you see the first signs of green, remove the cover.
Water, feed, repeat
As the seedlings grow, use a mister or a small watering can to keep the soil moist but not soggy. Let the soil dry slightly between waterings. Set up a fan to ensure good air movement and prevent disease. I use a fan that’s plugged into the same timer as my grow lights. Remember to feed the seedlings regularly with liquid fertilizer, mixed at the rate recommended on the package.
Light, light, light!
Seedlings need a lot of light. If you’re growing in a window, choose a south-facing exposure. Rotate the pots regularly to keep plants from leaning into the light. If seedlings don’t get enough light, they will be leggy and weak. If you’re growing under lights, adjust them so they’re just a few inches above the tops of the seedlings. Set the lights on a timer timer for 15 hours a day. Keep in mind that seedlings need darkness, too, so they can rest. As the seedlings grow taller, raise the lights.
Move seedlings outdoors gradually
It’s not a good idea to move your seedlings directly from the protected environment of your home into the garden. You’ve been coddling these seedlings for weeks, so they need a gradual transition to the great outdoors. The process is called hardening off. About a week before you plan to set the seedlings into the garden, place them in a protected spot outdoors (partly shaded, out of the wind) for a few hours, bringing them in at night. Gradually, over the course of a week or 10 days, expose them to more and more sunshine and wind. A cold frame is a great place to harden off plants.
A seed starting tray with a built-in watering system makes seed starting foolproof. Good-quality “potting soil” for seed starting doesn’t actually have any soil in it. This sterile, free-draining mix is perfect for seedlings.
Only one-quarter of my seeds germinated. What went wrong?
There are a number of factors that affect seed germination. Check the seed packet to determine if all the requirements for temperature and light were met. If the soil was cold and excessively wet, the seeds may have rotted. Dig up one of the seeds and examine it. If it is swollen and soft, the seed has rotted and you will need to start over. If the soil was too dry, the seeds may not have germinated or may have dried up before their roots could take hold. If the seeds were old, they may no longer be viable. Try again and be sure to provide consistent moisture.
My seedlings are spindly. What can I do?
Plants grow tall and leggy when they do not receive enough light. Use grow lights to ensure that they receive 15 hours of bright light each day. Warm temperatures can also stimulate leggy growth. Try lowering the room temperature and reducing the amount of fertilizer you apply. For more on this topic, see the article Growing Under Lights.
From our Garden Lab: The seedlings on the right were grown on a windowsill. You can see how the stems are long and spindly, with tiny leaves. On the left are seedlings grown under lights.
The tray on the left was grown with water-soluble fertilizer.
The leaves on my tomatoes are starting to look purple along the veins and on the underside of the leaves. What’s happening?
Purple leaves are an indication that the plant is not receiving enough phosphorus. If you have been using half-strength fertilizer for the first three to four weeks of the seedling’s life, it may be time to increase the fertilizer to full strength. The phosphorus content (the middle number on the fertilizer analysis) should be at least 3.
My seedlings were growing well until all of a sudden they toppled over at the base. What happened?
When the stems of young seedlings become withered and topple over, they have probably been killed by a soil-borne fungus called “damping off.” This fungus is difficult to eradicate once it is present in the soil, but you can avoid it by using a sterile, soilless growing medium, and by providing good air circulation.
Mold is growing on the top of the soil surface. It doesn’t appear to be hurting my plants, but should I be concerned?
Mold is an indication that the growing medium is too wet. It will not harm your plants as long as you take action. Withhold water for a few days and try to increase air circulation around the containers by using a small fan. You can also scrape off some of the mold or try transplanting the seedlings into fresh soil.
Growing plants from seed is a great way to start gardening earlier in the season. With the right light and some simple equipment, it's easy to grow from seed to harvest.
How to Grow Plants From Seeds Step by Step
Maybe you want grow plants from seeds to save money. It’s definitely cheaper than buying transplants. It will also be easier to find seeds of varieties not typically available for sale as transplants. Whatever the reason, starting plants from seeds is probably not a hard as you think. And growing plants all the way from seed to maturity is one of gardening’s most rewarding endeavors.
Here are the basics in 10 steps.
1. Choose a container.
Seed-starting containers should be clean, measure at least 2-3 inches deep and have drainage holes. They can be plastic pots, cell packs, peat pots, plastic flats, yogurt cups, even eggshells. As long as they are clean (soak in a 9 parts water to one part household bleach for 10 minutes), the options are endless. You can also buy seed-starting kits, but don’t invest a lot of money until you’re sure you’ll be starting seeds every year. If you start seeds in very small containers or plastic flats, you’ll need to transplant seedlings into slightly larger pots once they have their first set of true leaves. Keep in mind that flats and pots take up room, so make sure you have enough sunny space for all the seedlings you start.
2. Start with quality soil.
Sow seeds in sterile, seed-starting mix or potting soil available in nurseries and garden centers. Don’t use garden soil, it’s too heavy, contains weeds seeds, and possibly, disease organisms. Wet the soil with warm water before filling seed-starting containers.
3. Plant at the proper depth.
You’ll find the proper planting depth on the seed packet. The general rule of thumb is to cover seeds with soil equal to three times their thickness – but be sure to read the seed packet planting instructions carefully. Some seeds, including certain lettuces and snapdragons, need light to germinate and should rest on the soil surface but still be in good contact with moist soil. Gentle tamping after sowing will help. After planting your seeds, use a spray bottle to wet the soil again.
4. Water wisely.
Always use room-temperature water. Let chlorinated water sit overnight so chlorine can dissipate or use distilled water. Avoid using softened water. It’s important to keep soil consistently moist, but avoid overwatering, which promotes diseases, that can kill seedlings. Try not to splash water on leaves. An easy way to avoid this – as well as overwatering – is to dip base of your containers in water and allow the soil to absorb moisture from the bottom until moist. Some seed-starting kits supply a wicking mat that conducts water from a reservoir to dry soil. This may be the most goof-proof method of watering seedlings but you still have to be careful that the soil doesn’t stay too wet. Whatever you do, don’t miss a watering and let seeds or seedlings dry out. It’s a death sentence.
5. Maintain consistent moisture.
Prior to germination, cover your container to help trap moisture inside. Seed-starting kits typically come with a plastic cover. You can also use a plastic bag, but it should be supported so it doesn’t lay flat on the soil. Remove covers as soon as seeds sprout. Once seedlings are growing, reduce watering so soil partially drys, but don’t let them wilt.
6. Keep soil warm.
Seeds need warm soil to germinate. They germinate slower, or not at all, in soils that are too cool. Most seeds will germinate at around 78°F. Waterproof heating mats, designed specifically for germinating seeds, keep soil at a constant temperature. You can buy them in most nurseries and garden centers. Or, you can place seed trays on top of a refrigerator or other warm appliance until seeds sprout. After germination, air temperature should be slightly below 70°F. Seedlings can withstand air temperature as low as 50°F as long as soil temperature remains 65-70°F.
Start feeding your seedlings after they develop their second set of true leaves, applying a half-strength liquid fertilizer weekly. Apply it gently so seedlings are not dislodged from the soil. After four weeks, apply full-strength liquid fertilizer every other week until transplanting.
8. Give seedlings enough light.
Not enough light leads to leggy, tall seedlings that will struggle once transplanted outdoors. In mild winter areas, you can grow stocky seedlings in a bright south-facing window. Farther north, even a south-facing window may not provide enough light, especially in the middle of winter. Ideally, seedlings need 14-16 hours of direct light per day for healthiest growth. If seedlings begin bending toward the window, that’s a sure sign they are not getting enough light. Simply turning the pots won’t be enough – you may need to supply artificial lighting. Nurseries and mail order seed catalogs can provide lighting kits. Follow instructions carefully.
9. Circulate the air.
Circulating air helps prevents disease and encourages the development of strong stems. Run a gentle fan near seedlings to create air movement. Keep the fan a distance away from the seedlings to avoid blasting them directly.
10. Harden off seedlings before transplanting outdoors.
Before moving seedlings outdoors, they need to be acclimatized to their new, harsher surroundings. This procedure is called “hardening off.” Click here to learn more.
Want to start your plants using seeds? Following these 10 simple steps in the gardening process will teach you how to grow plants from seeds step by step.