Top 10 gardening tips for starting your seeds indoors
Starting seeds indoors is about as much fun a vegetable gardener can have in late winter in Greater Columbus. Starting seeds indoors will allow you to grow seedlings into transplants or starts in just two to eight weeks, depending upon the crop and the rate of growth, and then transplant these plants outdoors in your garden where the plants will mature and yield fresh, nutritious vegetables later this spring and summer.
Here are my top ten tips for successfully starting seeds indoors:
#1 – Select the correct seeds to grow indoors - Vegetables that can be successfully started indoors include Brussels sprouts, eggplant, kale, lettuce, greens, onions, okra, peppers, tomatoes, broccoli, cauliflower and cabbage. Some seeds which can be a little more difficult to successfully seed indoors include celery, chard, cucumber, melon, pumpkin, spinach and squash.
#2 – Seed at the proper time – The proper time to sow seeds indoors for transplants depends upon when they can be safely planted outdoors after the last frost in Greater Columbus. Coolseason crops such as lettuce and kale can be transplanted outdoors as early as March and can be started indoors in late February and through March. Warmseason crops such as tomato, eggplant, pepper and others should be seeded indoors approximately six to eight weeks before the typical date of last frost, which typically occurs around May 1. That means you can start seeding these crops indoors this coming week!
#3 – Avoid the use of native soil – Soilless seeding mixtures are the best media to use when starting seeds indoors. Even good-quality, loamy native garden soils with adequate organic matter are simply too heavy for proper germination and seedling growth when starting seeds indoors. These soils will also contain weed seeds and may harbor pathogens.
Many soilless seeding mixtures are available for purchase at local garden centers. These mixtures are sterile and typically contain a combination of peat moss, vermiculite and perlite. I prefer mixes containing vermiculite as this naturally occurring mineral aids in germination.
#4 – Only use clean containers – Many different types of containers are suitable for starting seeds indoors, including containers which you may already
have on hand. I like to use black plastic take-out food containers after I punch drainage holes in them. Small peat pots and plastic cell packs designed for planting seeds can be purchased
online or at local garden centers.
All containers must have drainage holes, and you will need to place trays under containers to catch excess water. Be sure that containers are properly sterilized before using them. Wash them in soapy water and then rinse with a solution of one part chlorine bleach and 10 parts water. Dry thoroughly before adding the growing mix.
#5 – Keep seedlings out of windowsills – The natural light from a window is seldom enough for good strong seedling growth. Seedlings grown in windowsills will produce thin spindly, and stretched stems which lean toward the light and the plants will lack vigor. Acceptable plant growth can sometimes be achieved in windowsills of south-facing, large bay windows and in solariums.
A better approach for growing seedlings indoors is to grow them under fluorescent light fixtures and grow lights, which allows you to adjust the duration of time that the light is available and the quality of the light, which includes blue and red wavelengths. Grow light kits suitable for seedling growing are available at local garden centers and online.
#6 – Temperature of soil is critical – The temperature of the seeding mix is more critical than the ambient temperature of the room in which you start your seeds. For optimum germination,
the temperature of the soilless seeding mixture should be a minimum of 70 degrees Fahrenheit, particularly for warmseason crops such as tomato, pepper and eggplant.
Consider purchasing an electric seed starting mat which will evenly heat your planting media to 10 to 20 degrees above the ambient temperature in the room. This is particularly important if you are growing your seedlings in a cooler room such as a basement.
#7 – Don’t over-fertilize – Seedlings draw energy for germination from nutrients stored in the seed. They don’t need to be fertilized until they have several sets of true leaves. Soilless mixtures do not contain nutrients, so a general-purpose water-soluble fertilizer should be applied just once a week when seedlings develop true leaves. Choose a fertilizer
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#8 – Keep seedling mix moist – Be sure to keep the seeding mix moist at all times, but not overly wet. Depending upon room temperature and light, you will need to water once or twice a week. Spray bottles can be useful for watering, particularly before and during germination.
#9 – Up-pot – If your seedlings outgrow the containers in which they are planted, you can transplant them into larger containers. Lift seedlings by the root ball using a spoon for support if necessary. Never hold the seedling by the stem as you may crush it or harm the growing point. Larger seedlings in larger containers will require more space and often another set of lights.
#10 – Harden off seedlings - Plants started indoors will not have been exposed to full sun, wind or fluctuating temperatures. If they are not gradually accustomed to the outdoor environment, a process called "hardening off," their leaves may be scorched by sun or wind. They may even wilt and die.
Two weeks before planting outdoors, move seedlings outside. Start by putting them outside for a few hours in the shade during the warmth of the afternoon, protected from wind. Bring them back inside before temperatures start to drop at night. Each day, leave the plants out a little longer, and expose them to a little more direct sunshine. By the end of two weeks, unless freezing temperatures are forecast, the seedlings can stay outside in a sunny area until you are ready to transplant them into the garden.
Mike Hogan is Extension educator, Agriculture and Natural Resources, and associate professor with Ohio State University Extension.
hogan.1@osu.edu