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What Are the Best Tips for Indoor Seedlings?

Rebecca Mecomber
Rebecca Mecomber

For some gardeners, planting indoor seedlings is born of pure pleasure. Others view starting seedlings indoors as sheer necessity, since some plants have very a long growing season and need an indoor start. No matter the reason, all seedlings have the same basic needs: a sterile and nutrient-rich growing medium, warmth, sufficient but not excessive water, appropriate light, and room to grow. Once the seedlings are ready to go outdoors, they must be properly acclimated to the outdoor environment. The gardener who supplies these needs will enjoy abundant fruits of his or her labors.

The first step for healthy seedling growth is sterile potting soil with vermiculite or sphagnum moss. Usually purchased at home and garden centers, sterile soil protects the delicate seedlings from any fungus or parasites lurking in topsoil or used potting soil. The soil should be placed in flats, or wide-mouthed plastic containers. Clay pots wick moisture away from the growing seedlings and should be avoided. Seeds should be planted at the recommended depth according to the seed manufacturer package for best results.

Woman with a flower
Woman with a flower

A common tip among gardeners is to wrap the seedling containers with clear plastic wrap until the seeds germinate, creating a miniature greenhouse. Once the seeds sprout, the plastic wrap should be removed to allow air circulation. To prevent the highly damaging fungal growth common with indoor seedlings, it helps to set a fan on low blowing over the tops of the seedling containers. The fan circulates the air, preventing the dreaded "damping off" that encourages fungal growth and early seedling death. Though indoor seedlings need water excessive amounts promotes fungal growth.

Seeds do not require light to germinate, but once the first green shoot sprouts from the soil, proper light is essential to growth. Most vegetable and fruit seedlings need an environment with 12 to 16 hours of sunlight and a general temperature around 70°F (21°C). Some gardeners supply artificial light, but the bulbs must be fluorescent and emit a combination of blue and red spectrum rays for growing seedlings.

Transplanting seedlings can be tricky. Inexperienced gardeners take their tender indoor seedlings and plant them in the outdoor garden, then wonder why their seedlings have died overnight. After living in a controlled climate since germination, seedlings must adapt to the outdoor environment in stages. This is called acclimation. For one week before transplanting, seedlings should be carried outdoors for a few hours during the day to adjust to the direct sun and wind.

Some gardeners place their seedlings in a cold frame to acclimate their plants to the outdoor life. A cold frame is a wooden box with a glass top. Seedlings placed in this box are protected from extreme wind gusts and slowly adapt to sunshine and outdoor temperatures.

Another helpful tip is labeling the pots to prevent confusion later. In the beginning, watermelon seedlings look strikingly similar to zucchini and muskmelon plants but each requires different placement in the garden. It helps to write the name of each seedling on a discarded popsicle stick and tuck the markers in their appropriate containers. Plants also respond well to touch. Periodically brushing the tips of the indoor seedlings encourages strong stem growth.

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