After Labor Day is a great time to plant many things. The risk of heat stress is reduced and, because evaporation is generally less of a problem, watering is easier. Also, in the fall most plants are not putting much energy into growth of branches, stems, flowers, or foliage; thus their energy can be applied to establishing roots.
GOOD CANDIDATES FOR LATE FALL PLANTING
If you find yourself in late October with an empty space in your garden that you want to fill before the winter, one of the following may be what you’re looking for:
• Daylilies (Hemerocallis). They won’t show flowers until next year, and the foliage is not its freshest in the fall. But horticulturally they are highly resilient and take late planting very well.
• Peonies (Paeonia). They can be planted right up to Thanksgiving.
• Deciduous trees and shrubs. These plants do not need to put as much energy into winterizing themselves as evergreens.
Good candidates include:
• lilacs (Syringa)
• sweetspires (Itea)
• twig dogwoods (Cornus shrubs)
• crabapples (Malus)
• several shade trees: maple (Acer), katsura (Cercidiphyllum), honeylocust (Gleditsia), ash (Fraxinus), plane tree (Platanus), and others
JUST A FEW CAUTIONS
• Grasses. This includes both perennial ornamental grasses and lawn seed. Ornamental grasses should be planted by October 10th. Seeding a new and overseeding an old lawn are best accomplished from September 1st to October 15th.
• Broadleaf evergreens – e.g., rhododendrons, evergreen azaleas, hollies (Ilex) of all sorts, andromeda (Pieris), mountain laurels (Kalmia), boxwoods (Buxus). Broadleaf evergreen foliage must endure winter wind and sun and generally needs time to prepare for the stress. Be sure to water through Thanksgiving and consider using an anti-desiccant/anti-transpirant spray.
• Hemlocks (Tsuga). For hemlocks it is very important to water through Thanksgiving.
• Follow our Container-grown Trees and Shrubs Planting Guidelines, available in hard copy at the Garden Center. Or follow our B&B Trees and Shrubs Planting Guidelines, available in hard copy at the Garden Center.
• With fall plantings it is particularly important to disturb the root balls of plants as little as possible. Even heavily root bound plants should be handled slightly more gently than during the spring or summer.
• Follow our Watering Guidelines, available in hard copy at the Garden Center.
• Keep watering until the ground freezes – not just until the first frost. Watering until the ground freezes hard (often mid December) is the cheapest insurance you can buy for your plant’s first winter survival, particularly for broadleaf evergreens.
• Be sure not to over water. Plants require less water than they do during the heat of high summer. The goal is to keep the root ball uniformly moist but not soggy, providing the equivalent of 1” of natural rainfall per week.
The best time to fertilize woody plants is September up to mid October; top growth has ceased and bud formation is almost complete, so nitrogen and other nutrients absorbed at this time are converted into stored carbohydrates, the energy reserve needed for strong growth the next spring. The mid October cut off is important – you don’t want to promote new growth that won’t have time to harden off. The next best time is in the spring before new leaves emerge. (Note that organic fertilizers are not effective unless soil temperatures are above 40 degrees F. Some gardeners will apply a slow release organic after the ground begins to freeze in December so that it is ready and waiting when soil temperatures rise in the spring.) Summer fertilization is usually discouraged.
Most gardeners apply mulch during the growing season to cut down on weeding and watering. Applying a winter mulch is a different technique with different goals.
• An additional blanket of light mulch insulates the ground from the warmer daytime air temperatures during winter. While it does not keep plants warm, it does help keep the ground frozen which prevents plants heaving out of the ground from repeated cycles of freezing and thawing. This is particularly true in sunny areas. Spread winter mulch after the hard ground freeze.
• Winter mulch can also create a physical barrier against drying winter winds and sun. For example, piling mulch high around the stems of some roses and hydrangeas not only regulates soil temperatures but mechanically protects the stems of easily winter-killed plants.
• Salt marsh hay, boiled shredded hay, straw, pine needles and oak leaves are ideal for this purpose because as they insulate they “breathe” without compacting and they do not shed fertile seeds. Be sure to remove winter mulches gradually as the soil warms in spring.
• Some plants resent having their crowns covered in any way, for example, Heuchera. Check with horticultural staff for recommendations for specific plants.