Tips for Planting in Fall
Whether supplementing an existing planting or installing an entire garden, the soil and air temperatures during autumn present the perfect conditions for root establishment. If you’re accustomed to planting only in the spring, here are few important tips to keep in mind as you plan an autumn plant installation.
- Take Stock at the End of Summer. At the end of summer it’s easy to remember the garden’s progress. Your observations of the past season are still visible: where to add a tall spiky plants, which areas needed more ground cover, spots that could use more early seasons blooms, and so on. Plan ahead. Determine which plants you need, and order early.
- When to Plant. Plant roots need time to become established. Ideally, plants should be installed at least six weeks before the ground freezes. We start shipping plants during the second week of September. The further North you live, the earlier you should plant.
- Plant Spring Ephemerals in Early Fall. Spring-blooming perennials are best planted early in the fall. Planting in the fall while the soil is still warm will give the roots enough time establish properly. This allows the plants to emerge from well established roots, with a stronger start, the following spring.
- Soil Temperature. The soil temperature is warmer in the fall than it is in spring, and this encourages root growth. Since most plants are not producing flowers, they have more energy for root establishment.
- What About Frost? Frost will stop the growth of the plant above ground, but it will not kill the plant. The roots will continue to grow until the soil freezes solid.
- Plant Condition and Dormancy. At the end of the growing season many native perennials have finished their growth cycles, and may start to look a bit "tired." Ephemeral plants will be completely dormant in the fall, with no growth showing above the roots. Because of this complete die-back, ephemerals are usually shipped as bareroot stock. Plants that bloomed earlier in the summer will also be well past their prime and getting ready for the winter dormant period. Simply plant them with the same care that you would give a thriving green plant in the spring.
- Watering. Before planting, water the plants thoroughly and let the roots completely soak up the water. With the lower temperatures, the lower sun angle, and the shorter days, plants generally need less watering in the fall. In the fall, watering once a week (until the soil freezes) is usually plenty. However, fall can have hot, dry spells when additional watering is needed.
- Mulching. Fall transplants do not need to be mulched immediately. The new growth will benefit from the sun warming the soil, even in October. The transplants should be mulched when the cold weather sets in – apply mulch when the night temperatures are hitting 32 degrees or lower and the soil is just beginning to freeze. Mulch material can be a thick cover of leaves, or other spent plant material, or straw. Remove the winter mulch in the spring, after freeze-thaw cycles have passed.
- Preventing Frost Heave. Once the plants are in the ground, a freezing and thawing of the soil can result in “frost heave” – wherein the thawing soil causes plants that aren’t fully anchored to raise up out of the soil. This puts the plant in danger of being killed by cold. Installing the plants early reduces the chances of frost heave (see #2). After the soil has frozen hard a good layer of straw will keep the ground from thawing around the plants (see #8).