Seed Starting & Transplanting

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The use of transplants enables the gardener to grow warm season vegetables to maturity outdoors, hasten maturity of cool-season vegetables and achieve a longer bloom period for many annual flowers. Based on usual home temperatures (68° to 72°F) with at least 10 hours of daylight, the average number of weeks needed to grow transplants to the proper sizes are indicated below. Subtract the number of weeks listed from the average date of the last spring frost in your locality to determine planting dates. Less favorable growing conditions may require the longer period of time.

FLOWERS

Flowers marked with an asterisk (*) do well in cooler temperatures of 50° to 55°F. Beginners will do well to try flowers from this group.

Six to Eight Weeks

• Butterfly flower Schizanthus
• English daisy Bellis perennis
• Feverfew Chrysanthemum parthenium
• Lobelia Lobelia sp.
• Nemesia Nemesia sp.
• Flowering tobacco Nicotiana sp.
• *Petunia Petunia hybrida
• *Snapdragon Antirrhinum majus
• *Sweet alyssum Lobularia maritima
• Verbena Verbena laciniata

Four to Six Weeks

• *African daisy (cape marigold) Dimorphotheca sp.
• *Ageratum (floss flower) Ageratum sp.
• Aster Aster sp.
• Godetia Godetia sp.
• *Larkspur Delphinium brownii
• *Nasturtium Tropaeolum majus
• Stocks Matthiola sp.
• *Bachelor button Centaurea cyaneus
• *Candytuff Iberis sempervirens
• *Clarkia Clarkia pulchella
• Dahlia Dahlia pinnata
• *Marigold Tagetes erecta
• *Phlox Phlox sp.
• Zinnia Zinnia elegans

For more detailed information on seed starting and plant propagation, see "Alaska's Sustainable Gardening Handbook," Chapter 4, Plant Propagation.

Four Weeks in Individual Containers

• Canary bird vine Tropaeolum peregrinum
• Mignonette Reseda odorata
• *Nemophila Nemophila sp.
• Sunflower Helianthus annus

VEGETABLES

SEED STARTING SCHEDULE CALCULATOR

Alternatively, plug-in your spring frost-free date into this online calculator: http://www.johnnyseeds.com/growers-library/seed-planting-schedule-calculator.html

Note that not everything in the seed starting calculator will reach maturity in Alaska, e.g., okra or watermelons. Crops with long maturity periods should be started earlier than suggested in this calculator.

MATERIAL NEEDED FOR STARTING TRANSPLANTS

Container

Almost any type of container can be used as long as it has adequate drainage and will last for up to three months when damp. Some possible choices include wood flats, plant pots, peat pots, peat pellets, tin cans, milk cartons, foil pie plates, plastic freezer cartons, etc.

Germinating Media

Although soil and potting mixtures may be used, they are NOT necessary to ensure germination. Vermiculite, sphagnum moss, sand, perlite or other STERILE material that can be kept uniformly moist is satisfactory. If a soil mixture is used, moisten and bake in the oven to sterilize (one-half hour at 180°F is sufficient). Sterilized media is required to prevent “damping off ” disease from killing seedlings. Fill containers to within ½ inch of the top. Seedling surface should be firm but not hard to provide good contact between soil and seed. All containers, tools and the working area must be clean and sterile to prevent reinfection. Wood and plastic can be sterilized with a mixture of one part chlorine bleach to nine parts water. Clean containers first and let stand in bleach solution for 30 minutes. Dry before reuse.

Seed Treatments

Many seeds from commercial sources are already treated with fungicides to prevent damping off. If they are not or if they are home-grown seeds, they should be treated. Contact your local district Extension office for recommendations on seed treating.

Damping Off

This is the major problem to watch for with new seedlings. Poor air circulation and/or crowded plants create ideal conditions for damping off. Increase air circulation and thin the plants at the first sign of trouble. Plants should have circulation of air at the soil surface. Cool, soggy soil and insufficient light also create conditions favorable for damping off.

SEEDING AND GROWING TRANSPLANTS

Seeding

Space or scatter seeds well apart. Nearly everyone plants many more seeds than can grow for even a short time. Plant in rows if more than one type of seed is used.

Covering Seeds

Cover very lightly. Fine seeds need no cover at all if kept moist. If covered, the surface should be firmed to insure good seed-soil contact. Cover should be to a depth of two times the seed diameter. Lettuce and celery seeds require light for germination.

Watering

Water seeds gently but thoroughly. Fog or mist is ideal to keep the surface moist. The container can also be put in a pan of water to absorb moisture from the base, which helps to avoid damping off by keeping the surface dry.

Covering the Container

A plastic cover, plastic wrap, or wet newspaper may be used to keep seeds moist until they germinate.

Heat

Place in an area where the temperature is about 70°F. Heat at the bottom of the container hastens seed germination. Avoid placing covered containers in direct sunlight. A few plants such as larkspur, snapdragon, sweet pea, cabbage, broccoli and cauliflower start best at about 55°F.

After Germination

New seedlings need light and fresh air. Remove newspapers, glass or plastic covers as soon as seedlings appear. If not all seeds germinate at the same time, keep ungerminated rows covered until seedlings appear. Strips of newspaper work well for this.

Light

Adequate light is essential for healthy transplants. Lights should be placed 2-4 inches above the plants. For more information on providing an artificial source of light, see "Controlling the Greenhouse Environment," HGA-00336.

Transplanting

If you didn't plant in individual cells, transplant seedlings to individual containers or flats filled with sterilized garden soil as soon as the first true leaves appear. Larger growing plants should be placed in individual containers. Handle plants gently by the upper leaves. Use a pointed stick (dibble) to roll out or "prick off " the seedlings. DO NOT PULL THE PLANTS. Avoid tearing the roots and replant at the same depth as the plant was growing in the seed flat.

SETTING PLANTS OUT IN THE GARDEN OR YARD

Hardening Off Plants

Before transplanting outdoors plants should be hardened off. Withhold water and carry them outside for progressively longer periods of time each day. As plants start to harden off, they may become slightly yellow with tinges of red at the edges of the leaves. Allow a week or more for this process. A cold frame works well for this procedure. Avoid wind or temperatures below 45°F. This transition period is important in harsh climates.

Starter Solution

Use a starter solution when transplanting to get plants off to a good start in their new environment. Follow mixing directions on the container carefully. Use ½ to 1 cup of solution per plant. A good solution is 1 tablespoon of high phosphorus water soluble fertilizer in 1 gallon of water.

Glenna Gannon, Extension Agriculture and Horticulture faculty, Originally prepared by Wayne Vandre, former Extension Agriculture Agent

Revised February 2023