Water. The first step in the germination process is the imbibition or absorption of water. Even though seeds have great absorbing power, due to the nature of the seed coat, the amount of available water in the germination medium affects the uptake of water. An adequate, continuous supply of water is important to ensure germination. Once the germination process has begun, a dry period will cause the death of the embryo.

Light. The light reaction is a complex process that may either stimulate or inhibit seed germination. Examples of plants requiring light for seed germination are ageratum, begonia, browallia, impatients, lettuce and petunia. Conversely, calendula, centaurea, pansy, annual phlox, verbena and vinca germinate best in the dark. Other plants are not specific at all. Seed catalogs and seed packets often list germination or cultural tips for individual varieties. When sowing seed that requires light, do as nature does and leave the seed on the soil surface. If the seed is covered at all, use a light layer of fine peat moss or fine vermiculite. If not applied too heavily, these materials will permit some light to reach the seed and will not limit germination. When starting seed in the home, suspend fluorescent lights 6 to 12 inches above the seed for 16 hours a day.

Oxygen. Respiration takes place in all viable seed. In nongerminating seed, respiration is low but some oxygen is required. The respiration rate increases during germination; therefore, the medium in which the seed is placed should be loose and well-aerated. If the oxygen supply during germination is limited or reduced, germination can be severely retarded or inhibited.

Heat. Favorable temperature is another important requirement for germination. It not only affects the germination percentage, but it also influences the rate of germination. Some seeds will germinate over a wide range of temperatures, whereas others require a narrow range. Many seeds have minimum, maximum and optimum temperatures for germination. For example, tomato seed has a minimum germination temperature of 50°F, a maximum temperature of 95°F and an optimum germination temperature of about 80°F. When germination temperatures are listed, they are usually the optimum temperatures unless otherwise specified. Generally, 65° to 75°F is best for most plants. Sometimes, germination flats may have to be placed in special chambers or on radiators, heating cables or heating mats to maintain optimum temperature. The importance of maintaining proper medium temperature to achieve maximum germination percentages cannot be over emphasized.

Germination will begin when certain internal requirements are met. A seed must have a mature embryo, contain a large enough endosperm to sustain the embryo during germination and contain sufficient hormones or auxins to initiate the process.

Methods of Breaking Dormancy. One of the functions of dormancy is to prevent a seed from germinating before it is surrounded by a favorable environment. In some trees and shrubs, dormancy is difficult to break even when the environment is ideal. Various treatments are performed on the seed to break dormancy and begin germination.

Seed scarification. Seed scarification involves breaking, scratching or softening the seed coat so that water can enter and germination can begin. There are several methods of scarifying seeds. In acid scarification, seeds are put in a glass container and covered with concentrated sulfuric acid at about twice the volume of seed. The seeds are gently stirred and allowed to soak from 10 minutes to several hours depending on the hardness of the seed coat. When the seed coat becomes thin, the seeds can be removed, washed and planted.

Another scarification method is mechanical. Seeds are filed with a metal file, rubbed with sandpaper or cracked with a hammer to weaken the seed coat prior to planting. Seed scarification can also be accomplished using hot water (170° to 212°F); the seeds are left to soak in the water as it cools for 12 to 24 hours before planting. A fourth method involves storing seeds in a nonsterile, warm, damp container where the seed coat will be broken down by decay over several months.

Seed stratification. Seeds of some fall-ripening trees and shrubs of the temperate zone will not germinate unless chilled underground as they overwinters. This so-called "after ripening" may be artificially accomplished through the practice of stratification.

The following stratification procedure is usually successful. Fill a clay pot with sand or vermiculite to about 1 inch from the top. Place the seeds on top of the medium and cover with ½ inch of sand or vermiculite. Wet the medium thoroughly and allow excess water to drain through the hole in the pot. Place the pot containing the moist medium and seeds in a plastic bag and close the bag using a twist tie or rubber band. Place the bag in a refrigerator. Periodically check to make sure the medium is moist but not wet; additional water will probably not be necessary. After 10 to 12 weeks, remove the bag from the refrigerator. Take the pot out and set it in a warm place in the house. Water often enough to keep the medium moist. Soon the seedlings should emerge. When the young plants are about three inches tall, transplant them into larger pots until time for setting outside.

Another stratification procedure that is usually successful uses sphagnum moss or peat moss. Thoroughly wet the moss and squeeze out excess water. Mix seed with the sphagnum or peat and place in a plastic bag. Use a twist tie or rubber band to secure the top and put the bag in a refrigerator. Temperatures ranging from 35° to 45°F (2° to 7°C) are effective, and most refrigerators operate in this range. Check the bag periodically; if there is condensation on the inside of the bag, the process will probably be a success. After 10 to 12 weeks, remove the bag from the refrigerator and plant the seeds in pots to germinate and grow. Handle the seeds carefully; often, small roots and shoots are emerging at the end of the stratification period and care must be taken not to break these off.

Seeds of most fruit and nut trees can be successfully germinated using these procedures. Peach seeds should be removed from the hard pit. Care must be taken when cracking the pits as any injury to the seed itself can provide an entrance for disease organisms.

Media. A wide range of materials can be used to start seeds, from straight vermiculite or mixtures of soilless artificial media to the various amended soil mixes. With experience, you will learn what works best under your conditions. Always keep the desirable qualities of a germinating medium in mind. The medium should be rather fine and uniform, yet well-aerated and loose. It should be free of insects, disease organisms and weed seeds. It should also be low in fertility, low in soluble salts, and capable of holding and moving moisture by capillary action. One medium with these qualities is a combination of one-third sterilized soil, one-third sand or vermiculite or perlite, and one-third peat moss.

The importance of using a sterile medium and container cannot be over emphasized. The home gardener can sterilize a small quantity of soil mixture in an oven. Place the slightly moist soil in a heat-resistant, covered container or pan in an oven heated to 250°F. Using a candy or meat thermometer, make sure the mix reaches a temperature of 180°F for at least one-half hour. This process typically produces very unpleasant odors. Avoid overheating as this can be extremely damaging to the soil. This treatment should prevent damping-off and other plant diseases as well as eliminate potential plant pests. Wood or plastic growing containers and implements should be washed to remove any debris, then rinsed in a 10 percent bleach/90 percent water solution. Avoid recontamination of the medium and tools.

To sterilize soil media in a microwave oven, place the moist soil media in a shallow, covered dish. Heat for 10 to 15 minutes on high and allow to cool before using.

A good germination medium can also be had with an artificial, soilless mix. The basic ingredients of such a mix are sphagnum peat moss and vermiculite, both of which are generally free of diseases, weed seeds and insects. These ingredients are also readily available, easy to handle, lightweight, and they produce uniform plant growth.

Readymade "peat-lite" mixes or similar products are commercially available or may be made at home. One homemade combination is 4 quarts of shredded sphagnum peat moss, 4 quarts of a fine grade vermiculite, 1 tablespoon of superphosphate and 2 tablespoons of ground limestone. Another combination is 50 percent vermiculite or perlite and 50 percent milled sphagnum moss with fertilizer. Mix thoroughly. Since these mixes have little fertility, seedlings must be watered with a diluted fertilizer solution soon after they emerge. Do not use garden soil alone to start seedlings; it is too heavy, is not sterile, does not drain well and will shrink from the sides of containers if allowed to dry.

Containers. Wooden or plastic flats and trays can be purchased or can be made from scrap lumber. A convenient size is about 12 to 18 inches long, 12 inches wide and about 2 inches deep. Leave cracks about 1/8 inch between the boards in the bottom or drill a series of holes for adequate drainage.

Flower pots of clay or plastic can also be used. You can make your own containers for starting seeds by recycling cottage cheese containers or using the bottoms of milk cartons, bleach containers or pie pans, as long as proper drainage is provided.

Numerous types of pots and strips made of compressed peat for starting seeds are also on the market. Plant bands and plastic cell packs are also available. Each cell or minipot holds a single plant; this reduces the risk of root injury when transplanting. Peat pellets, peat- or fiber-based blocks and expanded plastic foam cubes can also be used for seeding. In these cases, the growing medium itself forms the container unit.

Seeding. The proper time to sow seeds for transplants depends on when plants can be safely moved out-of-doors in your area (Table 2.1). This period may range from 4 to 18 weeks prior to transplanting, depending upon the speed of germination, the rate of growth and the cultural conditions provided. A common mistake is to sow the seeds too early and then attempt to hold the seedlings back under poor light or improper temperature ranges. This usually results in tall, weak and spindly plants that do not perform well in the garden.

After selecting a container, fill it to 3/4 inch from the top with the moistened medium you have chosen. For very small seeds, at least the top ¼ inch should be a fine, screened mix or a layer of vermiculite. Firm the medium at the corners and edges with your fingers or a block of wood to provide a uniform, flat surface.

For medium-to-large seeds, make furrows about 1 to 2 inches apart and 1/8 to 1/4 of an inch deep across the surface of the container using a narrow board or pot label. Good light and air movement results from sowing in rows, and if damping-off fungus appears, there is less chance of it spreading. Seedlings in rows are easier to label and handle at transplanting time than those that have been sown in a broadcast manner. Sow the seeds thinly and uniformly in the rows by gently tapping the packet of seed as it is moved along the row. Lightly cover the seed with dry vermiculite or sifted medium if they require darkness for germination. A suitable planting depth is usually about twice the diameter of the seed.

Do not plant seeds too deeply. Extremely fine seeds, such as petunia, begonia or snapdragon, are not covered; instead, they are lightly pressed into the medium or watered-in with a fine mist spray. If these seeds are broadcast, strive for a uniform stand by sowing half the seeds in one direction and the other half in the opposite direction.

Large seeds are frequently sown into some sort of a small container or cell pack, which eliminates the need for early transplanting. Usually two or three seeds are sown per unit and later thinned to allow the strongest seedling to grow.