sowing seeds indoors

Used with permission of Ohio State University Extension, Master Gardener Volunteer Manual.

Sowing seed indoors is the easiest and least expensive method of producing vegetables, annual flowers and some perennial plants. Plants with extremely small seeds or those that need a long growing season make excellent candidates for starting indoors.

Very small seed is difficult to plant outdoors because of size. Plants that require a long growing season may not have enough time to reach maturity unless started indoors in winter or early spring.

Supplies needed for indoor seed sowing include fluorescent or grow lights, disinfected containers with excellent drainage, pasteurized (sterile) seed-starting medium and a location with proper temperature and ventilation.

Choosing seeds
When choosing seed, be sure to select varieties or cultivars that meet your requirements for size, color and growth habit. Choose varieties that will mature before frost. This can be estimated by using the number of days to maturity (found on the seed packet or in the catalog) and comparing it to the days between probable planting date and the average frost date of the area.

When considering seed not packaged for the current year, remember that the germination rate of most seeds drops dramatically after the first year.

Seed catalogs are not only helpful in purchasing seed, but they are also excellent references for cultural information. Catalogs and seed packets may provide information on country of origin, bloom time, specific germination requirements, cultural requirements and disease resistance. Some seed packets indicate if seeds have been chemically treated to prevent disease. Read packets and catalogs thoroughly and follow their recommendations. The more information the gardener possesses, the greater the chance of growing plants successfully.

Growing media
Choose a medium with a loose, uniform, fine texture. A pasteurized mixture that is 1/3 soil, 1/3 sand, vermiculite or perlite, and 1/3 peat moss has the qualities of a good seed-starting medium. Retail garden centers carry mixes labeled for seed starting. Whatever is selected, be sure it is pasteurized (sterile). Using pasteurized soil prevents damping-off, a fungal disease that kills young seedlings. Pasteurized soil also helps to avoid weeds, diseases and pests.

Seed-starting media are usually low in fertility. This means that a regular fertilization program is very important once seedlings emerge.

Containers
Any recycled containers are adequate for seed starting provided they are disinfected, have good drainage and are at least 2 inches deep. Other container options include compressed peat pellets, peat pots, paper pots, plastic cell packs and flats.

Peat and clay containers tend to dry more quickly than plastic containers because they are very porous.

Sowing seed
The correct timing of seed sowing is an important factor in successful indoor seed starting. In winter months, overanxious gardeners may sow seeds too soon. Seedlings that are held indoors too long perform poorly once transplanted into the garden. Most seeds should be sown 4 to 12 weeks prior to transplanting into the garden. The time it takes for seedlings to be ready for transplanting outdoors will vary.

An acclimation period before placing seedlings directly into the permanent growing site must be included. However, readiness for outdoor planting will vary with how quickly germination occurs, the growth rate and weather conditions. Quality and quantity of light, temperature and nutrients affect the growth rate. Seed catalogs and packets provide information on days to germination and weeks needed to reach transplant size.

How to
Fill the container to within 1/4 inch of the top of the container with moistened seed-starting medium. After sowing seeds, keep the medium moist, not wet. To keep the medium moist, you may place the container in a plastic bag just large enough for the container. Seal the bag. The plastic bag keeps moisture in, but allows air exchange. The plastic bag method should not require any further watering until germination. Provide proper light and temperature conditions.

Once seedlings germinate, remove the container from the plastic bag. Place the container in a location that has high light intensity and cooler temperatures.

Use the following rules to sow seed, depending upon seed size. Sow very small seeds by sprinkling on top of the medium and pressing in. Use a fine mist of water to gently wash seed into the growing medium. Sow medium-size and larger seed in rows 1 to 2 inches apart, and 1/8 to 1/4 inches deep. If no depth is specified on the seed packet, use the general rule of planting the seed at a depth twice the diameter of the seed.

When sowing in a tray or flat, sowing in rows is preferred over scattering seed. This method provides better air circulation than scattering of seed. When seedlings are crowded, they may become tall and spindly. To avoid the need to transplant seedlings from a seed flat to pots, you may sow seeds directly into cell packs or peat pots. Plant two or three seeds per cell or pot. When they germinate, remove the two less vigorous seedlings.

Transplanting
Once the seeds have germinated, you will see two seed leaves or cotyledons. Eventually, these seed leaves will wither. Next, true leaves will form. These true leaves look like the plant's typical leaves. Transplant the seedlings to individual containers once the first set of true leaves appear.

Use a pencil, small stick or other narrow tool to lift seedlings from the seed flat. Plant each seedling in its own small pot filled with pasteurized growing medium. The new container should be no larger than a 2-1/2- to 3-inch pot.

Hold the seedlings by a leaf between the thumb and forefinger. Handling by the leaf avoids damaging the fragile stem, which would kill the seedling. If a small leaf is lost in transplanting, the plant can recover and grow normally. Expose seedlings' roots to air as briefly as possible. Lightly firm the soil around the seedling.

Transplanting temporarily slows or stops the growth of seedlings. Sowing into cell packs bypasses the need to transplant the seedlings.

Watering seeds indoors
Watering can be a cause of seedling failure. Keep soil moist but not wet. Small, tender seedlings dry out rapidly and can die. Remember that roots always must have oxygen, as well as water; therefore, do not keep the soil soaked. Water when the surface of the soil begins to dry out.

Bottom watering helps prevent damage to the seedlings caused by a hard stream of water. Bottom watering also encourages deep root development and ensures that the entire depth of soil receives moisture. Do not let the pot or flat sit in water longer than it takes for all of the soil to become moist.

Seedling temperature
Keep seedlings in a well-ventilated, cool location. The temperatures should be 55 to 60 degrees F at night and 65 to 70 degrees F during the day. These temperatures encourage compact, bushy, vigorous growth while minimizing disease.

Light requirements
Seedlings require bright light immediately after germination. One warm-white, 40-watt bulb and one cool-white, 40-watt bulb used together are adequate for seed starting and seedling growth. Fluorescent lights can be used for one year before replacement is recommended.

Special grow lights are also suitable, but more expensive. The lights should be no more than 6 inches above the top of the seedlings. Mount the light fixture so it can be raised as the plants grow in height.

Day-length requirements vary with different plants. Petunia, snapdragon, phlox and China aster require short daylight periods of 10 to 12 hours. However, most plants that are started from seed benefit from 16 to 18 hours of light.

Fertilizing
Because the growing medium used to start seedlings is usually low in nutrients, a regular fertilization program is important for proper plant growth. Apply a liquid fertilizer high in phosphorous weekly. Fertilizer with a 1-2-1, N-P-K ratio is recommended. Dilute fertilizer 1/4 to 1/2 the label's recommended strength and apply sparingly. Always use a liquid form of fertilizer.

Pinching seedlings
Pinching the growing tips of seedlings will result in more branching. This produces a fuller, stockier plant.

Hardening off seedlings before transplanting into the garden
Plants grown indoors must be gradually introduced to outdoor conditions. If seedlings are not hardened off, leaves may be burned by the intensity of the sun or damaged by wind. Acclimate plants by first placing them in a cool, protected location, such as a porch or shaded cold frame.

This first step in hardening off allows plants to adjust to outdoor temperatures. After 7 to 10 days, move seedlings into a shaded area of the garden for 2 to 3 days. This will prevent sunscald. Finally, hardened seedlings can be planted directly into the garden as weather permits. Planting on a cloudy day or late in the evening is a sensible precaution.

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