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Starting Seeds Indoors

Starting Seeds Indoors

By Ashleigh Smith, True Leaf Market
Photographs courtesy of True Leaf Market

If you have experience gardening, you are likely acquainted with starting seeds indoors. If just starting out, you may wonder why this is necessary. It all comes down to the length of your growing season. Regions experiencing frost have a shorter season. A short growing season means you can only grow certain plants or specific varieties when directly planting into the ground. I don’t know about you, but I don’t like feeling limited.

Using season-extending tools and practices, like starting seeds indoors, can add weeks to your growing season. Familiarize yourself with the needs of each seed and make plans ahead of time for planting, transplanting, and for properly caring for plants throughout the season. Some seeds may need specific conditions in order to germinate, while others may not grow indoors or transplant well at all. As a rule, vegetables should be started indoors 6-8 weeks before your last spring frost. Flowers are often closer to 10-12 weeks, but vary widely.

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When starting seeds indoors, choosing the right trays and inserts is key. In my opinion, a sturdy container that can drain excess water is ideal. If you are regularly growing from seed, a reusable 6-cell container is a must. You will always have a tray ready for the next season, saving you time and money. If you are growing a lot of seed starts, such as flowers, I would recommend a 288-plug tray. These trays allow you to save space during the initial germination and sprouting phase of seed starting. Then, transplant your seed sprout to a larger sturdy container until you are ready to plant. For easy tray transport, be sure to use a mesh tray that allows you to move them as you please, while still draining excess water.

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Once you have chosen your trays, move on to picking the right seed-starting soil. A seed provides enough energy to support plant development until the true leaves start developing. Then, it starts to rely on nutrients in the soil. This is why seed-starting mixes focus on providing a light and spongy environment ideal for root development rather than nutrient support. For indoor seed starts that won’t be transplanted for several weeks, prioritize finding an amended seed starting mix including nutrients to support vegetative growth into the flowering stage. Or use a reliable fertilizer when the seedling reaches at least three inches tall. Seeds started in plug trays or pellets can be grown in an unamended soil growing medium, as they will be transplanted to a larger container before the seedling requires additional nutrients.

Germinating seeds is a simple process that nature has mastered, and we must imitate. Generally, seeds like moist, dark and temperature-appropriate surroundings. Usually, seeds germinate best in warm temperatures. A cool and moist environment may lead to rotting before the seed can germinate. However, cool-season seeds that sprout quickly, like leafy greens, grow well during the cool spring months. Support your seeds with a heating mat if needed. Check the growing requirements of your seeds for special circumstances such as direct sunlight, cold stratification or heat. The seeding depth will usually indicate if sunlight is needed. A surface level up to one-eighth of an inch indicates sunlight is required for germination. A light dusting of soil can help maintain needed moisture levels. For keeping seeds moist, I recommend using a hand or pump spray bottle.

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Stratification is the process of mimicking seasonal change. Thawing soils and an increase in precipitation are an indication that seeds will survive if sprouted. You can mimic this by storing your seeds in a freezer for 3-4 weeks before planting. As the seed warms to the moist soil, your seeds will recognize it is time to sprout. Because the seed is waiting for the appropriate signal, germination may take longer than other seeds. You can find stratification requirements on either the seed packaging or the website product page. Most seeds will benefit from a brief soaking in water to encourage germination by softening the seed coat. Avoid soaking extra small or pelleted seeds.

Once seeds have been selected, soaked or stratified (if needed), they are ready for planting. Follow your planned schedule and the provided growing instructions. Either sow into a tray insert with individual cells or plugs, or broadcast into a 10x10 or 10x20 tray. Each germinated seedling may be transplanted into its own container, making sure every available space is filled with a successful seedling.

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Plants started indoors may be transplanted to their final growing location when they have at least two sets of true leaves, an established root system and are hardened off. The first “leaves” developed are cotyledons, with rounded, small leaflets from the stored seed energy. True leaves follow. When grown indoors, plants are tender and sheltered from the quick changes of the outdoors. By exposing them to the open air for increasing amounts of time each day, a protective “thick skin” is developed. This process is called hardening off. The process can be compared to developing a tan. If a person spends twenty minutes sitting in the sun after being cooped up all winter, they may get a sunburn that quickly subsides. However, spending increasing amounts of time outside each day will result in a darkening tan. Continuing to increase the time plants spend outdoors will strengthen them.

When starting seeds indoors, remember to select, plan, sow, care, and transplant. Select seeds that meet your needs and are appropriate to your growing location. Make plans, including when to plant, specific needs, and when to transplant. Care for the young seedlings. Harden off, and transplant at the appropriate time. If low temperatures, hail or heavy rains are expected after transplanting, you may need to protect your crops from damage. I find that using a tarp or large sheet of plastic is easiest for covering a large area. Overall, starting seeds indoors isn’t difficult. The key is to mimic the ideal outdoor growing conditions and understand special growing requirements.

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Ashleigh Smith is the Managing Editor at True Leaf Market with a bachelor's degree in Horticulture from Brigham Young University - Idaho. True Leaf Market is a national certified organic, non-GMO seed and horticultural company based in Salt Lake City, Utah. The True Leaf Market staff specializes in supplying a large selection of conventional, heirloom and organic seeds to home gardeners everywhere. Learn more about our seeds, supplies and other growing ideas:

All articles are copyrighted and remain the property of the author.

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