Warm soil temperatures Air temperatures drop in fall, but the ground stays warm after months of summer sun. Whether you're sowing wildflower seeds for a mini-pollinator meadow, planting garlic cloves, or planting a new flowering shrub, warm soil temperatures encourage seed germination and root growth. In autumn, the perfect combination of warm soils and milder weather creates ideal conditions for newly planted trees, shrubs and perennials. Warm soil temperatures favor root growth, more so than in spring, when the soil is still warming.
In addition, with shorter days and cooler air temperatures, plants spend less energy growing foliage and flowers and more on building a strong root system in preparation for winter. Planting in fall takes advantage of this, as it allows our garden plants to meet next spring with a strong root system, ready to generate many new shoots as soon as they warm up. And for any plant, transplanting can be stressful: cooler air and more consistent soil moisture in the fall make it a little less. Planting in fall has some of the same benefits as planting in spring.
Temperatures are usually cold, causing plants to lose less water through their leaves due to perspiration than when it's hot. This reduces the chances of plants experiencing stress and more energy can be used for root production. When the air temperature drops below the ground temperature, sprout growth stops and roots continue to develop until the soil drops below 40°F. In addition, significant rainfall tends to occur in autumn, which also helps woody plants to settle in.
A healthy and well-established root system goes a long way in ensuring vigorous growth in the spring. Colder fall weather causes less stress on new plants, allowing root systems to establish themselves in a comfortable environment before winter. For this reason, plants such as magnolia, tulip, oak and ginkgo are more suitable for planting in spring. Plants with fibrous and shallow roots are often the best options for planting in the fall because they recover faster than those with large, thick main roots.