Knowing when each plant should be sown is an important factor in growing a flourishing garden. Unfortunately, the planting guidelines on seed packets or in gardening magazines are rarely precise enough to be helpful. For better results, information from local gardeners, frost date guidelines, biological cycles, and even the phases of the moon can be used to pinpoint the ideal planting time for each vegetable, flower, or tree.
Many gardeners understand that getting each plant in the ground at the right time is vital for growing a healthy garden, but what do you do when the information on the seed packet just says ”plant in spring”? When the host of a national gardening program tells you it’s time to plant squash, how can you be sure that statement is accurate for your region? Correct planting times can’t be chosen according to a date on the calendar, but there are a number of reasonably accurate methods for determining them.
Contact Local Gardeners The easiest way to find out when a particular plant should be sown or transplanted is to contact a local nursery, garden center, or agricultural extension, or find an experienced gardener through a local gardening club. This way, you can simply provide the name of the plant and what part of town you live in and you’ll get a fairly accurate estimate. When asking for advice, don’t just accept a fixed date. Be sure you understand how the expert determined the planting date they suggested.
Planting Relative to the Frost Date Another method is to choose planting times relative to the last and first frosts in the region. The U.S. Department of Agriculture’s system of plant hardiness zones is the most popular guideline for predicting frost dates in North America. Similar maps have also been created for Europe, placing inland Britain in zone 8 and the British coasts in zone 9. Central Europe falls into zones 7 and 6, with the Mediterranean in zone 10. Detailed zone maps have been developed for individual countries and can be found through an Internet search or by asking at your local garden center. Soil temperature is another factor determining when a plant should go into the ground. For accuracy, rather than relying on weather forecasts to tell you soil temperatures, use a soil thermometer to take measurements exactly where you want to plant at a depth of 3-4 in (8-10 cm). While using predicted frost dates and soil temperature to choose planting times works most years, it still exposes plants to the risk of an untimely frost.
The Old Farmer’s Almanac This venerable old book, first published in 1792 by Robert Bailey Thomas, provides a planting timetable and detailed weather forecasts for each of 16 regions throughout the U.S. and Canada. The publishers claim Thomas’ weather forecasting methods, which are now supplemented by modern science, have been 78 to 80 percent accurate since their conception. Unfortunately for non-U.S. gardeners, the weather information will be difficult to use unless you know which region of the U.S. is similar to your own.
Phenology The name of this method is Greek for “the science of appearances”. Annual occurrences--or “appearances”-- in the growth of plants and the behavior of wild animals are used to determine when cultivated plants should be sown, fertilized, sprayed, or pruned. Although the principle has been used since ancient times, it’s becoming an ever more exact science with practitioners around the world keeping detailed records of the yearly cycles in their gardens. Because this method allows nature to indicate appropriate planting times, it’s quite precise.
Planting by the Moon While this system won’t tell you which month to plant in, it can help determine which week of the month the ideal planting time will occur in. To calculate this time, the system takes into account how the moon’s gravitational pull affects plant growth. In general, above-ground crops are best planted while the moon is waxing (rising), while root crops should be planted during the waning (declining) moon. For example, it’s recommended that flowers and fruit plants be put into the garden when the moon is waxing.
All five of these methods can be combined to pinpoint the ideal planting time for each species of plant within an individual garden. Naturally, though, each type of plant has unique requirements that must be considered.
Bulbs
Spring-flowering bulbs such as tulips, daffodils, and hyacinths should be planted in the autumn, four to six weeks before the first frost. Because spring-flowering bulbs need a period of dormancy to germinate, in climates with no winter frost, bulbs will have to be chilled in the refrigerator from approximately November to March or forced in pots. For summer-flowering bulbs, the planting time is late spring, six to eight weeks after the last frost. According to the tradition of planting by the phases of the moon, bulbs should be planted when the moon is waning, between the full moon and last quarter.
Perennials
Perennial flowers and herbs should be planted either in early spring or early autumn. Almost all can be planted in spring when there is no longer any danger of frost. Some perennials such as phlox (Polemoniaceae ssp.), alyssum (Lobularia maritima), and most wildflowers, along with cool-season herbs like dill and cilantro, can be planted in autumn. To give these plants time to establish themselves, plant them four to six weeks before the first frost. Turf grasses and ornamental grasses are also perennials. Cool-season grasses such as Kentucky bluegrass, fescue, and rye grow best if sown two or three weeks after the last frost in spring, but before the summer heat arrives. These grasses can also be sown in autumn four to six weeks before the frost, but should be kept watered and protected with mulch or a similar covering. Warm-season grasses such as Bermuda, big bluestem, and and zoysia prefer air temperatures between 70 and 90 F (20-30 C).
Annuals
Garden centers usually display annuals before the plants are ready to go into the garden, so don't assume that because you can by them they’re ready to make it on their own outdoors. Annuals planted too early in the spring may end up stunted by the chilly weather and never fully recover. They may also fall victim to a late frost. On the other hand, annuals planted too late in the season won’t have time to mature enough to bloom well. Nearly all annuals, especially warm-climate natives like bleeding heart (Clerodendrum thomsoniae), Amish cockscomb (Celosia cristata), and coleus (Coleus blumei), should be planted when air temperatures are in the 70 and 80 F (20-25 C).
Vegetables
Soil texture and temperature are the most accurate indication of when to plant vegetables. As a general guideline, vegetables that grow in spring should be planted in late winter, summer vegetables in early spring, and autumn vegetables in summer when temperatures are beginning to fall. Again, though, what type of weather determines “spring”?
For most vegetables, spring means when soil temperatures are consistently above 50 F (10 C). Even if the soil is warm, though, avoid planting if it’s still muddy, as wet soil tends to harden and make it harder for plants to put down roots. Soil is ready for planting when it can be formed into a ball that crumbles easily. Once soil temperatures are between 65 and 75 F (15-25 C), summer vegetables can be planted. Keep in mind, too, that the terms "cool-season" and "warm-season" refer to a plant’s preferred growing conditions, not planting times. If you live in a desert or tropical climate, some cool-season vegetables like beans and lettuce won’t survive the summer and should be planted as early in the year as possible. The good news, though, is that a second crop can be planted when the weather cools to the 70s F (20s C).
While it’s risky to sow too soon after the frost, the long growing seasons required by some vegetables make it critical to get these plants started early. Another benefit of an early start is that the earlier vegetables are planted, the less likely they are to experience insect problems. In areas with short growing seasons, plants can be started indoors so that they’re ready to be transplanted to the garden as soon as the appropriate weather arrives. Sow indoors just early enough to give the plants time to become strong seedlings. Plants sown indoors too early may become spindly from lack of light and space.
The Old Farmer’s Almanac and phenology are particularly useful for vegetable gardening. While the Almanac’s information is conveniently gathered in one book, phenology resources usually have to be sought locally. Some guidelines are relatively well-known, though. For example, tradition holds that Native Americans in New England planted corn when the oak leaves were the size of squirrels’ ears. Potatoes should be planted when the soil temperature is in the 50s F (10-15 C), which is approximately the temperature in which forsythia comes into bloom.
If you’re taking guidance from the moon, the new moon is the best time to plant fruits or vegetables that bear their seeds on the outside, such as strawberries, lettuce, spinach, and grains. Melons, peas, tomatoes, and other plants that carry their seeds inside should be sown or transplanted when the moon is waxing, between the first quarter and full.
Trees and Shrubs
Trees and shrubs bought from nurseries were usually dug during the dormant period. These trees can be planted in either autumn or spring, so long as they receive sufficient water. Otherwise, trees and shrubs should be planted in the autumn after they have become dormant (near the time of the first frost) or in early spring before new growth appears. If your region has mild winters, but hot, dry summers, autumn planting will give trees time to establish themselves while the weather is still cool. If your winters are relatively harsh, though, plant trees and shrubs during the spring after the snow has melted and the danger of frost has past.
Other Factors That Affect Planting Times
Frost guidelines can help determine ideal planting times, but local conditions like slopes, light levels, and frost pockets also matter. While the U.S. Department of Agriculture frost guidelines may work in New England, West Coast gardeners will want a more detailed zone map. The proximity of coastal, desert, and mountain conditions in the west mean that, for best results, each garden should be assessed individually.
High-altitude or high-latitude areas also have special requirements. In northern or mountain regions, short growing seasons mean warm-season vegetables will have a better chance if started indoors and planted in the garden three or four weeks after the last frost. However, what high-altitude summers lack in length they make up for in hot, dry weather. This means that until seedlings become established, they may need to be shaded from the mid-day sun.
Weather patterns can also vary considerably from year to year. Apart from asking local gardeners, the best way to learn the rhythm of your garden is to simply experiment and track your results. Keep your own phenology records of when wild plants flower or produce fruit and when certain insects or animals appear in the garden. It can also help to record the last and first frost dates and planting times as projected by The Old Farmer’s Almanac or your favorite gardening resource to see if they’re accurate for your garden.
Intricate as your plans may be, you can't predict Mother Nature's actions and from time to time new plantings will be lost to an unexpected cold snap. However, by using frost date guidelines and paying attention to the timing of annual occurrences in your garden, you’ll not only spare a few seedlings, you’ll have a healthier garden, as well.
External Links:
The Old Farmer's Almanac - Offers planting time guidelines, weather forecasts, pest control tips and other advice for home gardeners.
Life Cycles Phenology Software - Guidelines and tips for practicing phenology in your own garden. Shareware phenology software also available.
Gardening by the Moon - Detailed information on planting and caring for the garden based on the phases of the moon.
U.S. National Arboretum - Detailed map of the U.S. Department of Agriculture's plant hardiness zones