Q: I always think of spring as planting season. Why do gardeners say fall is actually a better time to plant?
A: Spring gets most of the attention, but in DC, September and early fall can be an even better time to add plants to the garden. By September, the worst of summer’s heat is usually beginning to ease, while the soil remains warm from months of summer sunshine. That combination — cooler air and warm soil— is nearly ideal for establishing many trees, shrubs and perennials.
In spring, newly planted plants face an immediate challenge: summer is coming. Their root systems may have only a few weeks to become established before DC’s heat and humidity arrive. Plants installed in September have a different experience. They can concentrate on growing roots without simultaneously coping with extreme heat and producing lots of new foliage and flowers.
Q: Isn’t September sometimes still pretty hot in Washington?
A: Absolutely. Anyone who has gardened here knows that summer doesn’t necessarily disappear after Labor Day. September can include plenty of 80- and even 90-degree days.
The difference is that days are getting shorter, nights are generally becoming cooler, and the sun is less intense. As fall progresses, plants lose less water through their leaves. Rainfall can also become more helpful as temperatures moderate, although newly planted plants should never be left entirely to Mother Nature.
The important thing is to water deeply after planting and continue checking soil moisture throughout the fall. A plant that looks dormant above ground may still be developing roots below the surface.
Q: What should I plant in September?
A: This is an excellent time for many deciduous trees and shrubs as well as hardy perennials. It’s also a particularly good opportunity to add native plants that provide food and habitat for birds and pollinators.
Good choices for DC gardens include:
- Eastern redbud (Cercis canadensis), a relatively small native tree with beautiful pink spring flowers.
- Serviceberry (Amelanchier), which offers spring flowers, summer berries for birds and attractive fall color.
- Oakleaf hydrangea (Hydrangea quercifolia), a native shrub with showy flowers, interesting bark and colorful fall foliage.
- Virginia sweetspire (Itea virginica), a versatile native shrub that tolerates a range of conditions and develops excellent fall color.
- Purple coneflower (Echinacea purpurea), a familiar native perennial whose flowers attract pollinators and whose seeds feed birds.
- Asters, especially native species, which provide valuable late-season nectar.
- Goldenrods (Solidago species), important late-season pollinator plants that are available in varieties suitable for even relatively small urban gardens.
Q: Are there plants I shouldn’t put in the ground in fall?
A: Yes. September isn’t automatically the best planting time for everything. Plants that are marginally hardy in our area or particularly sensitive to winter conditions may be safer planted in spring, giving them an entire growing season to become established.. Don’t wait too long with trees and shrubs. While planting can continue well into fall, September and October give roots more time to establish before the ground becomes cold.
Q: What about spring-flowering bulbs?
A: Fall is bulb-planting season, but daffodils, crocuses, alliums and other spring-flowering bulbs can generally be planted later in fall. Tulips, in particular, are often better planted after the soil has cooled.
Q: What’s the most important thing I can do for something I plant this fall?
A: Water it. Fall planting is forgiving, but newly planted trees, shrubs and perennials still need consistent moisture until they become established. Water deeply rather than giving plants frequent shallow sprinklings, and add a layer of mulch to conserve moisture and moderate soil temperatures. Keep mulch away from tree trunks and plant crowns.
Want to learn more about gardening or spend time with people who like plants? For more information go to the Capitol Hill Garden Club website at capitolhillgardenclub.org. Send your questions to capitolhillgardenclub@gmail.com.
