Are Fall (and late Summer) Really a Good Time to Plant?
By Jan Cashman • Posted on September, 9th 2010
In the spring, after a long winter, we are all thinking of gardening and planting. And we know, in Montana, spring is a good time to plant. But, is fall also a good time to plant? We, at Cashman Nursery, have had good success with late summer and early fall planting. For spring flowering bulbs, it is the only time to plant, and for grass seed, the best time. And for trees and shrubs, the soil temperatures are perfect for root establishment as the weather cools and they enter dormancy.
Trees and Shrubs
Although bare root trees and shrubs are not available in our area in the fall, as they are in the spring, most nurseries do have potted trees and shrubs available. These potted trees and shrubs will transplant well as long as they are not planted too late. One reason late summer and early fall planting works well is because root development is at its best after vegetative growth has stopped and soil temperatures have cooled some (50-55 degrees is optimal for root activity.). If you wait too late into the fall to plant, the soils are too cold and not enough root growth will take place to give the tree the roots it needs to make it through the winter.
Some trees and shrubs do better with fall planting than others. Spruce and ash seem to transplant especially well in the fall. Cottonwoods (Populus) and oaks may not do as well when fall planted.
We have found that between August 15 and September 10 is the best time to seed a lawn in our area. During this time the soil temperatures are still warm enough for rapid seed germination, yet the weeds are starting to go dormant. Because it tends to be so dry during this time of year, however, you will have to take extra care to keep the grass seed moist enough for it to germinate—sometimes having to water it several times a day. We do not recommend seeding after September 10 because we cannot be insured of enough warm days for the new grass seedlings to develop size and strength to make it through the winter.
Spring flowering bulbs such as tulips, daffodils, hyacinth, allium, and crocus, can only be planted in the fall. The bulbs grow leaves and bloom in the spring, store food in the bulb after blooming, and then can be dug in mid-summer. Once planted in the fall, the bulbs will grow roots and get ready to flower before going dormant during the cold winter. Do not plant tulips too early in the fall—warm weather could fool the tops into starting to grow.
German bearded iris are not true bulbs but rhizomes. They should be planted as soon as they arrive in the nurseries, usually mid-August because iris do not store long once dug.
When fall planted, daylilies, hardy lilies, and peonies all get a jump on spring. Fall planting allows the flower to put its energy into root growth in fall. Then in the spring the strong root system supports more top vegetative and flower growth.
Many people associate mums with fall. Hardy varieties of mums can be fall planted even when in full bloom but should be planted in a sheltered location and mulched in order to make it through our winters.
Clifford Shipp, who grows over 300 peonies south of Bozeman, recommends fall planting for peonies for a couple of reasons. The fall and winter months are when the buds are developing and the roots are processing nutrients taken in after the summer bloom is over. These nutrients will feed next year’s flowers. Clifford feels spring planting of peonies puts undue stress on the root to develop root hairs, foliage, and blooms.
So go ahead and plant this fall. Get a jump on spring. But remember, early fall works better for trees, shrubs, and grass seed.
Autumn Watering Tip
What does “decrease watering trees and shrubs” really mean?
Deciduous trees and shrubs should receive very little water now, only enough to keep the ground from cracking. (Deciduous trees are the ones which lose their leaves every winter.) Since evergreen trees do not lose their leaves over the winter, they continue to photosynthesize at cooler temperatures and not go dormant yet, water these trees regularly. This means to apply as much water as needed to saturate the entire root zone, and then wait until the top couple of inches of soil dries before watering again. For newly planted trees and shrubs, use the latter watering pattern. About Halloween, after the leaves have fallen, give all evergreen and deciduous trees and shrubs a thorough soaking to go into winter with a moist root zone. If throughout winter snow pack is low and the ground exposed, give any exposed areas a thorough soaking to keep the soil from cracking and allowing freezing air to the root zone.