Timely Tips on Starting Seedlings at Home

By E. E. Janne, Extension Landscape Horticulturist (deceased), and Dr. R. E. Roberts, Vegetable Specialist (retired), Texas A&M University, College Station, Texas

Starting transplants from seeds in your home is a good way to get a head start on the growing season. At least 4 to 8 weeks can be cut from the time required between planting and harvesting or of getting effective landscape color by setting vigorous transplants rather than seeds into the garden.

Growing your own plants may be the only way to obtain a new or special variety you want. Commercial plant growers cannot be expected to grow all of the hundreds of varieties offered by seedhouses. And, plant nurseries are often reluctant to offer varieties which have not been given widespread publicity.

Growing Media
Use of a loose, fertile, disease-free soil mix is a basic key to success. To prepare a mix of this type combine by volume one part sandy loam with one part sand or vermiculite plus one part Michigan or Canadian sphagnum peat. Anyone having clay loam should use one part soil to two parts sand or vermiculite and one part peat.

The mix must be pasteurized to kill harmful fungi,bacteria, weed seeds and nematodes which it may contain. This is easily done by placing the soil mix in a shallow metal pan, covering the pan tightly with aluminum foil and heating the soil to 160o in an oven. Keep the soil at this temperature for at least 1 hour or until a potato imbedded in the soil is baked. After cooling, the soil is ready for planting.

Premixed, soilless material can be bought in nurseries and stores. Soilless mixes are more expensive than the home mix but can be used right from the bag without pasteurization. These mixes are economical when used carefully. The following soilless mix can be prepared at home if the ingredients are available in a local nursery or through a catalog.

This "peatlite" mix is excellent for starting seeds and growing seedlings to transplant size.

The peat mixes with the other ingredients more easily if it is moist - not soaking wet. The night before, spread the dry peat out and sprinkle with just enough water to dampen it, or dampen in the bag. Follow these steps in mixing the ingredients:

  1. Pour the dampened peat moss or shredded pine bark and perlite or vermiculite in a rough pile. Sprinkle the fertilizer over the top.

  2. Shoveling from the base of the pile, make a second cone-shaped pile by pouring each shovelful directly on top so ingredients dribble down the sides.

  3. Shovel from the second pile and repeat the cone-shaped pile as before.

  4. Repeat the process again. It should now be well mixed. Store the mix in clean plastic bags or plastic cans to keep it moist and clean.

Any shallow wood, metal or plastic container at least 3 inches deep makes a suitable plant growing box. Milk cartons, foam cups, peat pots, and egg cartons make nice individual plant containers. Punch holes in the bottom of any carton, cup or pan to allow water to drain from the soil.

Sow seeds in rows 2 inches apart in a box of soil. If seedlings touch, remove some and transplant to give them more room to grow. If enough growing space is available, plant seeds directly into individual pots thereby eliminating the initial transplanting.

Regardless of the starting method, gardeners should allow proper space for each plant to develop. Crowded seedlings become stretched and unhealthy.

Consult Table 1 for the optimum seeding date. Peppers require 7 to 8 weeks and tomatoes 5 or 6 to grow to transplanting size. Squash and cucumbers require only 2 to 3 weeks to grow to an ideal size. Members of the cabbage and lettuce families need 4 to 5 weeks. Flowering annuals also vary in the time required to produce a size suitable for transplanting. Much depends on local growing conditions. It is important to keep a garden notebook and record seeding dates, length of time to germinate and time required to reach transplant size. Seedlings are ready to transplant when they have the first set of true leaves.

Table 1. Planting and growing information for vegetables.

Kind of vegetableWeeks needed to grow transplants*Seed planting depthOptimum temperature for germinationPlant-growing temperatures
Cabbage, broccoli and cauliflower5 to 71/4 to 1/28560-7050-60
Lettuce4 to 61/4 to 1/27560-7050-60
Onions8 to 101/27560-7045-55
Tomatoes5 to 61/4 to 1/28570-8060-65
Peppers7 to 81/4 to 1/28570-8060-70
Eggplant7 to 81/4 to 1/28570-8065-70
Cucumber, squash, muskmelon and watermelon2 to 33/4 to 18570-9060-70
*Depends on type of plant-growing structures used, heating facilities, and lighting available.

Soil temperature is important. Cool soil retards germination. Warm the soil to about 75o if possible until seedlings have emerged above the soil surface.

Provide an air temperature of 70o to 75o during the day and night temperature of at least 60o to 65o.

Cover the seed only enough to make it disappear from view [rule of thumb: 2X their diameter]. The seed packet usually gives correct planting depth. After seeding, water the soil gently but thoroughly until water drains out the bottom of the container, being careful not to wash seeds away. Place containers in plastic bags or cover the soil surface with plastic film until the first sign of seeding emergence. Then remove the plastic cover immediately and be sure the container gets maximum exposure to light. Most seeds do not require light to germinate, but seedlings need full exposure to light as soon as they emerge.

Begin transplanting when the first true leaves are forming, usually 2 to 3 weeks after sowing. Set the seedling at the same level it was in the seedling flat. When firming the soil avoid injuring tender stems.

Immediately after transplanting, water each seedling container thoroughly. Wilting at this point can damage young plants severely. To prevent excessive wilting, shade plants from strong sunlight for 2 or 3 days after transplanting.

Frequently, plant quality suffers from crowding too many plants into a small area. Crowded seedlings become weak and spindly and are more susceptible to disease. Wider spacing or larger containers permit stronger growth. As a rule of thumb, to produce high quality plants, space them so that the leaves of one plant do not touch those of another.

Add water to soilless media only when moisture can no longer be squeezed out by pinching the medium between the thumb and forefinger. Water soil only when it no longer feels moist when rubbed between the fingers. Apply enough water at each irrigation so that some drips out of the drain holes in the bottom of the container. Be sure the water is passing through the rootzone-not just down the inside wall of the container.

After seedling emergence and during early development, strong, rapid plant growth can be assured by watering the soil with a carefully prepared solution of a soluble fertilizer which is specifically designed for plant production. Prepare the solution exactly as prescribed on the label. Apply the solution as an irrigation when water is needed. Apply the solution as an irrigation when water is needed. Apply enough to allow some to flow out the drain.

Problems--An aid in diagnosing plant-growing disorders

SymptomsPossible causesCorrective measures
Spindly growth or leggy plants1. Shade causes excessive elongationFull sunlight whenever possible
2. Prolonged cloudy weather during growing seasonMaintain lower temperatures during cloudy weather. See Table 1
3. Excessive wateringWater when necessary to maintain a moist but never wet soil condition
4. Temperatures too highSkillful management of temperatures. See Table 1
5. Excessive fertilizerApply fertilizer less frequently and/or reduce the concentration
6. Poor plant spacingAt all times provide young plants with adequate space for stocky development
Dwarf plantsLow fertility. Severe cases will be accompanied by nutrient deficiency symptoms. See A1 and A2 belowNutrient levels difficult to maintain because of small volume of soil. Apply fertilizers often and in low concentrations.
A. Leaves discolored1. Phosphorus deficiency. plants dwarf early in growth; stems are slender, fibrous and hard. Underside of leaves and stems becomes reddish-purple. Leaves are small and roots stunted. Soil may be too acid.Apply a high-phosphorus plant-starter solution, such as a 10-55-10, 10-52-17 or 15-30-15 analysis. Use 2 tablespoons to 1 gallon of water.
2. Nitrogen deficiency. General indication of nitrogen deficiency is lack of green in the retarded growth with stems and leaves. If the soil is very deficient in nitrogen, symptoms may appear early in the seedling stage. If there is adequate nitrogen to support early growth only, deficiency symptoms may appear later.Apply nitrogen in water. Dissolve 2 teaspoons of ammonium nitrate or 3 teaspoons of ammonium sulfate per gallon of water. Be sure to wash solution from foliage with plain water after fertilizing.
B. With root discoloration1. Excess soluble salts from overfertilizing. Plants wilt in bright sunshine. Lower leaves turn yellow and drop off, and plant finally dies or has very small root system which is often discolored.Leach excess salts. Not generally a problem where regular feeding schedule is maintained. Maintain a moist soil condition.
C. Without root discolorationLow temperature. Retarded growth.Maintain proper day and night temperatures. Do not start plants too early.
Tough, woody plantsPlants likely to be over-hardenedApply plant starter solution 3 to 4 days before setting out. Use analysis such as 10-55-10 or 10-52-17 at the rate of 2 tablespoons (1 ounce) to a gallon of water.
Decay or rotting of the stems of young plants near the soil surface.Damping-off. Disease organisms attack germinating seeds and young plants, especially during prolonged cloudy weather.Use of sterilized soil-mix, skill in watering and ventilating and proper regulation of temperature.
Retarded root growth1. Poor soil mixtureAll factors influencing root growth are especially important. Root growth and formation of new roots are dependent on the food supply from the plant top, good aeration, ample supply of nutrients, adequate moisture and temperature.
2. Poor soil aeration
3. Poor drainage
4. Lack of fertility
5. Excess soluble salts
6. Low temperature
Green algae and mosses growing on soilSuch growth usually occurs on soils with a high moisture content. It is more evident in shade and when prolonged cloudy weather exists during the plant-growing season. Under these conditions, moisture is retained near the soil surface, making conditions favorable for its growth. Poor soil structure, poor aeration.Increase air movement around plants and practice morning watering. Add coarse, aggregate material to loosen the media, to decrease its water-holding capacity and to increase its air space.

Planting and Growing Information for Flowering Annuals

Columns A, B, C and D in the table refer to the following:

Column A--Optimum soil temperature for best germination.
Column B--D-Seeds germinate best in darkness; DL-No light requirements; L-Seeds germinate best in light.
Column C--Usual number of days required for uniform germination at optimum temperature.
Column D--Time (in weeks) needed to grow transplants.

Ageratum70oFL5 days6-8
Alyssum70oFDL5 days3-5
Calendula (pot marigold)70oFD10 days7-8
Carnation (annual)70oFDL20 days11-12
Celosia70oFDL10 days8-9
Coleus65oFL10 days7-10
Cosmos70oFDL5 days6-8
Dahlia (from seed)70oFDL5 days6-8
Dianthus (annual pinks)70oFDL5 days6-7
Dusty Millers
Centaurea gymnocarpa65oFD10 days7-8
Others75oFL10 days6-7
Gaillardia (annual)70oFDL20 days7-9
Impatiens (sultana)70oFL15 days4-6
Lobelia70oFDL20 days5-6
Marigold (dwarf types)70oFDL5 days6-7
Marigold (tall types)70oFDL5 days3-4
Pansy65oFD10 days10-12
Petunia70oFL10 days5-7
Phlox drummondi (annual phlox)65oFD10 days5-6
Portulaca (rose moss)70oFD20 days4-6
Rudbeckia (coneflower)70oFDL10 days6-7
Salvia splendens70oFL15 days5-6
Snapdragon65oFL10 days5-7
Verbena65oFD20 days5-7
Vinca rosea (periwinkle)70oFD15 days7-8
Zinnia70oFDL5 days3-5

This article appeared in Horticulture Update - January-February 2001, edited by Dr. William C. Welch, and produced by Extension Horticulture, Texas Agricultural Extension Service, The Texas A&M University System, College Station, Texas.

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