Getting Started With Seeds
Gunpowder and Bibles made history in the Old West, but garden seeds made pioneering possible. In a letter Narcissa Prentice Whitman mailed from the nascent community of Vancouver, Washington, in 1836, she wrote: "We brought an assortment of seed from Cincinnati with us over the mountains. . . . When Brother Weld comes, please remember to fill his pockets with peaches, plums, and pear seeds, some of the best kind, and some good seed; what they have here is not of the best kind nor a great variety. Another very important article for us housewives, some broom corn seed."
Gardening life is much simpler now, at least when it comes to seeds of "the best kind" and "a great variety." You'll never be asked to fill your pockets with peach pits. But if obtaining seeds is easier than ever (see "Seed Sources"), growing from seeds is much the same as it's always been, a process that still turns all of us into pioneers.
We adventurers have one thing going for us. A seed may have a low profile, but its entire business in life is to grow into a plant. The catch is that it doesn't want to waste its only shot by sprouting under the wrong circumstances. Giving it the go-ahead may be no more difficult than soaking it and waiting for the root to pop out, much the way you do when you grow bean sprouts.
Soil blocks are cubes of planting mix compressed in special molds. (Photo: Karan Davis Cutler)
Beans are typical of the seeds that have had a long working relationship with humanity. They've become domesticated, the vegetable equivalent of a Holstein cow or a poodle. A domesticated seed, given enough warmth and water, will obligingly proffer a root pretty well any time of year. It's fortunate that the seeds people have grown for a long time are likely the ones you, too, will want to grow. Some of those seeds, such as apple seeds, take more coaxing: a number of hardy perennials, shrubs, and trees are downright fussy about sprouting. The cones of Rocky Mountain lodgepole pines (Pinus contorta var. latifolia), for instance, need the heat of a forest fire to open and free their seeds to germinate; seeds of Oregon-grape (Mahonia aquifolium) require four to six months of warm temperatures, then three to four months of cold to sprout. But when you grow common garden annuals, both flowers and vegetables, you're like a pioneer following a well-worn trail. Simply stay on the path and you'll end up with flowers and vegetables, just as your forebears did.
To find the trail, you'll need a supply of quality seeds. Old seeds or seeds that have been improperly stored may be dead. Some seeds last for a very long time, but others need to be sown when fresh. Most members of the dill family (Umbelliferae), for instance, should be sown fresh every year. On the other hand, a seed of the sacred lotus (Nelumbo nucifera) germinated after 1,200 years in storage. Closer to home, basil seeds remain viable for at least five years if stored in a dry, cool location, and sunflowers for at least seven. If you're in doubt, buy or harvest a fresh supply, then store your leftovers properly (see "Collecting and Storing Seeds").
You'll also need to fulfill a few seed requisites. Many species don't need much, but even easy plants like beans have two requirements for sprouting: a suitable air temperature and a certain amount of moisture. Once germination takes place—unless your goal is crunchy sprouts for a sandwich—the seedlings will need containers holding soil or a similar porous medium in which the roots can grow. You can garden hydroponically in nutrient-enriched water, but this chapter assumes you are growing your seedlings for an eventual life in soil. Sooner or later, your plants will also need bright light and moisture.
Timing Is (Almost) Everything
When should you sow your seeds? This depends upon three variables: the type of seeds, your climate, and when you want your flowers to bloom or your vegetables to mature.
Type of Seeds
Seeds vary greatly in the length of time they take to germinate. Given moisture and an optimum temperature range, some species, such as cress (Lepidium sativum), sprout in as few as two days; most garden seeds germinate in a week or two. If conditions are close to ideal and nothing has sprouted in a month, give up and start again. The longer the seeds take to germinate, the earlier you should be sowing them.
Different plants also take different lengths of time to mature, so you should pace your sowing accordingly.
The last spring frost and the first fall frost in your garden are benchmarks around which all planting dates are calculated. Plant growth slows or stops when temperatures drop to freezing. Furthermore, many plants are killed by frost, so they must be protected if their lifespan overlaps the frost dates. In spring, the customary means of protection is to start seeds indoors then transplant them outdoors when the weather is warm. Much later—around or after the frost-free date—the seeds of frost-tender plants may be sown outdoors. (See "A Time to Sow") To find out the frost dates for your area, contact the local horticultural society, Extension Service, or weather bureau.
Timing the Bloom or Harvest
While late winter through early summer is the main seed-sowing time -- and the time when the best selection of fresh seeds is available—some species can be sown any time of year. Certain hardy annuals, for instance, can go into your garden beds any time in winter or spring, though they won't germinate until the soil warms to their liking. Some of these flowers include Shirley, or field, poppy (Papaver rhoeas), California poppy (Eschscholzia californica), cosmos (Cosmos bipinnatus), and clary salvia (Salvia viridis). Once you grow these flowers, you may never have to sow them again. They drop their seeds in summer, and these seeds again wait until conditions suit them to germinate. Fewer vegetables self-sow, but you might want to stagger plantings of certain vegetable seeds to extend the harvest. In regions with cold winters, lettuce and radishes can be sown every two weeks from early spring until early summer, then again in autumn, to provide salads for many months.
A Time To Sow—Indoors
These are suggested timings for indoor sowing of common plants. The number of weeks in the lists that follow refers to the time before the average date of the last spring frost in your area. For example, if your frost-free date is May 15, sow celery 12 weeks earlier, February 20. (Alternately, all of these plants can be seeded directly outdoors around or after the last frost date, al-though they will probably mature later.)
- Ten to twelve weeks: celery, eggplant, leek, onion, pepper, eustoma (Lisianthus), impatiens, lobelia, pelargonium, verbena, and many perennial flowers
- Seven to nine weeks: early lettuce, globe artichoke, parsley, ageratum, begonia, coleus, nicotiana, petunia, salpiglossis, and salvia
- Five to six weeks: early cabbage, cauliflower, late celery, early leaf lettuce, and most small-seeded annual flowers
- Four to five weeks: basil, cucumber, gourd, melon, pumpkin, squash, large-seeded annual flowers, and annual flowering vines
A Time To Sow—Outdoors
- Five to seven weeks: broad bean, carrot, pea, spinach, turnip, onion sets, dill, parsley, alyssum, candytuft, pansy, poppy (Papaver and Eschscholzia species), black-eyed Susan (Rudbeckia hirta), clary salvia, snapdragon, annual stock, sunflower, sweet pea, and shrubs such as pea-tree (Caragana) and bush-clover (Lespedeza)
- Three to four weeks: all in the list above; also beets, broccoli, Brussels sprout, cabbage, collard, chard, kale, lettuce, potato eyes, radish, Canterbury-bells, clarkia (Godetia grandiflora), hollyhock, and mallow
- Two to three weeks: All in lists above; also sweet corn, gladiolus and other summer bulbs, morning glory and other annual flowering vines.
- Around the last spring frost: All of the above; also bean, peanut, cauliflower, cucumber, summer and winter squash, lavatera, marigold, and zinnia
- One to two weeks after the last spring frost: All in the lists above; also lima bean, soybean, muskmelon, watermelon, sweet potato slips, basil, summer savory, sweet marjoram, and castor bean
Unless you use soil blocks, seeds sown indoors will need containers. Because these containers will be used for only a short time, they don't need to be deeper than two or three inches. However, they must allow water to drain out the bottom, and they should hold enough soil so the seedling will not be constantly drying out or instantly rootbound. Either give each seedling its own container, in which case the containers can be as small as an inch wide (the cells of the plastic four- or six-packs in which commercially grown seedlings are sold are fine, but the cells of an egg carton are not deep enough), or grow seedlings together in undivided containers or flats. Seeds can be sown fairly thickly, either in rows or in a cluster of several seeds, but once they germinate, they should be thinned so that each plant never touches its neighbor.
Plant pots, plastic dairy containers, plastic baked-goods containers, or cardboard milk cartons (either on their ends or on their sides, the top cut away, and the bottom perforated) all make suitable containers. Just make sure they are clean before you plant, and punch some holes in the bottom. Cover these holes with a single piece of newsprint to prevent soil from flowing out with the drainage water.
Absorbent or permeable containers, such as terra cotta or peat pots, are much more susceptible to drying out than plastic containers. Soak them before sowing, and afterwards, if necessary, keep them in a shallow bath of water to prevent drying, which will happen from the outside in. If a container has held soil in the past, it may be contaminated with fungal spores. Scrub previously used containers in a solution of one part household bleach to nine parts water.
Soil for seeds sown indoors should be porous, lightweight, and sterile. All three demands can be met if you purchase a seed-starting mixture from a garden store (to make your own seed-starting medium, see "Make & Bake"). Unlike commercial potting soils, which are too heavy for starting seedlings, these special mixes are a combination of ingredients, usually peat, vermiculite, and perlite, perhaps with the addition of limestone and wetting agents. Vermiculite and perlite are mineral products that expand with heat; they are lightweight, sterile, and will hold several times their weight in water. Soil for seeding need not include fertilizer, as seeds don't require nutrients to germinate, but many seedling mixtures do include fertilizer because the seedlings will require it later on.
Seed-starting mixtures may be damp when you first open the bag, but they will soon dry out. Before using them for seeding, pour the amount you need into a pail or large bowl and stir in enough warm water to make a doughy, wet mixture. Then pack the containers lightly to within 1/4 inch of the rim so that when you water, it won't overflow. Water again before seeding.
Some Like It Hot
You may have noticed that certain weeds sprout outdoors early in spring, while others appear much later. That's because some seeds can germinate in soil as cold as 40°F, while others require a soil temperature of 55°, 60°, or higher. So it is with the seeds that you sow. If the temperature is right for them, they'll germinate relatively quickly. If temperatures are cooler than they like, germination will be slower. If the soil is too cold—or wet—the seeds may not sprout at all. Soil that is too hot can prevent germination also.
For most common plants sown indoors, a room temperature between 60° and 80° is fine for sprouting. The optimum temperature range for germination is often listed on the seed packet or in the seed catalog. Incidentally, this temperature is that of the soil medium, not necessarily the air, although the two are usually within a few degrees of each other.
If you keep your thermostat turned down or your flats on the floor, you may have to provide additional heat to germinate seeds. Heat is most efficiently used and most beneficial to the seeds and seedlings if it comes from below. There are electric seed-starting mats and cables on the market that provide a gentle bottom heat to containers placed on top, or you can set seeded containers over a mild heat source, such as the top of a refrigerator. Don't place your containers where their seeds or seedlings will bake—temperatures over 95°—and remember that bottom-heated soil dries out more quickly, so check daily to see if watering is necessary. Also stay away from the warm top of your furnace, as its fumes inhibit germination of many species.
Getting A Headstart
Presprouting seeds, which is germinating seeds before they are planted, has two advantages. One, it means that you plant only viable seeds and thus won't waste good seeds by overplanting and then having to thin. Two, it means you can germinate your seeds in a warm place indoors even if you don't have room for a half-dozen flats or pots. For most households, an entire garden's worth of tomatoes, peppers, or tender flowers—some of the best candidates for this treatment—can be presprouted on a surface area not much bigger than a loaf of bread. Don't try to presprout tiny seeds, which are difficult to handle, and don't presprout seeds that dislike handling, such as cucumber and other members of the squash family.
To presprout seeds, you must keep them moist and warm. It is easiest to use a damp paper towel spread on the bottom of a covered container, such as a cottage cheese tub. Before you wet the towel, write the cultivar names on it in ballpoint pen. Press the towel into the container, dampen it with lukewarm water, sprinkle the seeds over it -- about 25 percent more seeds than the number of plants you want, to make up for poor or slow germination—and cover the container. Put the container in a place that is warm but never hotter than 90°. Check the seeds every day, moistening the towel if necessary, then transplant the seeds to flats or other containers as soon as a tiny root emerges. The planted seedlings can stay in the same warm place until a green shoot shows above the soil surface; then they must be moved into bright light.
Most seeds need darkness to germinate and must be covered with moist seedling mix, usually twice as deep as the thickness of the seed. To sow in flats, make furrows with a knife blade or with the edge of a ruler pressed into the soil; for individual containers, make an indentation with a pencil or your fingertip before setting the seed or a few seeds in place. Cover seeds lightly. Sow roughly twice as many seeds as the number of plants you want, since you will lose about half to nongermination, thinning, and transplanting. Seeds of a few plants, such as celery, dill, bellflower, coleus, nicotiana, and stock, germinate better in light than in darkness and should be scattered on an uncovered, moist soil surface rather than covered.
If the seeds are very fine, as those of ageratum, begonia, and petunia are, make sure the planting surface is damp, level, and lightly pressed before sowing. Sprinkle some seeds into the palm of your hand and wipe them as evenly as possible over the soil surface with the fingers of your other hand. Don't let the soil surface dry out—a spray bottle turned to its finest setting is good for daily misting. Set the containers in an area with diffused light, such as a few feet from a window or near but not under fluorescent lights.
There are a few species, such as primulas, whose seeds need darkness but don't want to be covered. Sprinkle these seeds on the surface of a dampened soil mix and press them down lightly. Then place the containers in a dark spot or cover them with pieces of cardboard or newsprint. Check under the covers daily. As soon as you see green shoots, remove the covers and move the containers into light.
If seeds have unusual germination needs, such as light or especially high or low temperatures, they will usually be described on the seed packet or in the seed catalogue. If nothing is said and the seeds are for familiar species, you can assume that they require the typical light covering of damp soil.
Seeds sown directly outdoors should also be kept moist until they germinate. Wet the ground and then make furrows or indentations. Sow about three times as many seeds as the number of plants you want, covering to the depth recommended on the packet, or about three times the diameter of the seed. Space small seeds like carrot about 1/8 inch apart, medium-sized seeds like beet about 1/2 inch apart, and large seeds like pea 1 or 2 inches apart. If you're sowing in a permanent location, create rows that are far enough apart to allow for easy weeding and walking. Seeds of plants that will become large, such as cabbage, broccoli, or cucumber, can be sown in stations, a few seeds together in a cluster that is eventually thinned to only one or two plants. Stations, or hills, are usually spaced a foot or two apart.
Check the seeded area every day, and water the surface with a fine spray if it dries out. In a very dry, windy climate, you may need to cover areas sown with fine seeds, such as carrot, with boards or fabric to hold in moisture. Leave the covers in place for a few days, then check for signs of sprouting. As soon as green shoots appear, remove the covers but continue to water as needed.
Moisture is necessary to trigger germination. It is important that the seed-starting mixture be uniformly damp before you plant into it. Flats and other containers can be placed in a saucer or pan of warmish water for constant bottom watering, although too much wetness encourages fungus diseases. Bottom watering works best with containers like terracotta or peat pots that dry out quickly. In other cases, it is better to use a fine mist to spray the soil surface whenever it begins to dry. Remember, finally, that the temperature of the water you use to water seeds—and the emerging seedlings—is just as important as soil temperature. Indoors, the water should be at least room temperature; outdoors, the water should be the ambient (air) temperature.
The seeds of some species will germinate more quickly if given special treatment. Among the germination-speeding methods you may see recommended on seed packets and in garden books are:
Some hard-shelled seeds, such as sweet pea and balloon vine, benefit from the outside coating being scratched or nicked to speed germination. One easy way to scarify seeds is to rub them lightly between two pieces of fine sandpaper. Abrade only the outer coating—you don't want to harm the embryo within.
Some seeds requiring scarification
- Camellia species, Camellias
- Cercis canadensis, Redbud
- Cladrastis kentukea (C. lutea), Yellow-wood
- Cornus florida, Flowering dogwood
- Gleditisia triacanthos, Honey locust
- Koelreuteria paniculata, Golden raintree
- Paeonia suffruticosa, Tree peony
- Rosa blanda, Meadow rose
The germination of some seeds can be speeded up if they are soaked in lukewarm water for several hours before planting. It is important to plant these seeds immediately after soaking and to water them thoroughly after planting. They must not be allowed to dry out again before germination occurs.
Some seeds requiring soaking
- Abelmoschus esculentus, Okra
- Albizia julibrissin, Mimosa or silk tree
- Armeria species, Thrift
- Cytisus species, Brooms
- Helianthus species, Sunflowers
- Ipomoea species, Morning glories
- Lupinus species, Lupines
- Pastinaca sativa, Parsnip
- Pisum sativum, Pea
- Wisteria species, Wisterias
The seeds of many plants that are native to regions with cold winters require a period of moist coolness before they will germinate. This process of applying moist cold, called stratification, can be mimicked indoors and need not take all winter. Three to five weeks are usually sufficient, and the temperature in a refrigerator, just above freezing, does the job. Mix the seeds with damp peat moss and place in a small, labelled plastic bag tied with a twist tie, or a sealed glass jar. When rootlets appear inside the bag or jar, take it out of the refrigerator and plant the seeds in pots. Place the containers under grow lights or in a cool, bright window.
Seeds can also be stratified outdoors, either by sowing them directly into garden beds or in plastic pots in the fall. Pots should be overwintered against a north-facing house wall or in a cold frame -- some place that offers protection against full sun and wind. Set the pots into a bed of straw, fallen leaves, or grass clippings, which will insulate them and allow drainage. Water if their soil becomes dry.
Some seeds requiring stratification:
- Acer species, Maples (except red maple [A. rubrum] and silver maple [A. saccharinum])
- Aesculus species, Buckeyes, horse-chestnuts
- Amelanchier species, Shadbushes, serviceberries
- Cornus species, Dogwoods
- Iris species, Irises
- Magnolia species, Magnolias
- Pinus species, Pines
- Rosa species, Species roses
- Thalictrum species, Meadow rues
- Vitis species, Grapes
Seeds of the bean, or pea, family (Leguminosae) may germinate and grow better if they are inoculated with certain strains of soil bacteria. In many cases, these bacteria are naturally present in the soil, especially if the plant or a relative has grown there before. Otherwise, inoculants can be purchased from suppliers of farm and vegetable seeds. The inoculant is a powder that is mixed with the seeds just before they are sown. Inoculation is usually done only when it's important that the harvest be as large as possible; for instance, in the commercial growing of soybeans. (Don't confuse seeds that have been inoculated with Rhizobium bacteria with seeds that have been treated with Captan or other toxic pesticides. Avoid seeds that have been doused with chemicals; seed catalogs that offer treated seeds usually offer untreated seeds as well.)