The soil temperature is warmer in the fall than it is in spring, and this encourages root growth. And since the plants are usually not producing flowers, they'll have more energy for root establishment.
Planting. Most perennials should be planted in the fall or early spring. Fall planting gives the plant more time to become established before the start of active growth in the spring. Fall-planted perennials are usually well-established before hot weather.
Fall is Good for Root Growth
Warm soil temperatures encourage root growth – more so than in the spring when the soil is still warming up. Plus, with the shorter days and cooler air temperatures, plants spend less energy on growing foliage and flowers and more on building a strong root system in preparation for winter.
Transplant perennials when the weather is cool, even a little rainy, if possible. Early spring and fall care are best times for transplanting. Then the weather is cooler and the plants are not using as much water. “However, don't move or transplant perennials while they are in bloom,” he says.
Some Plants Are Especially Cold Hardy
Many cold hardy perennials, shrubs and trees are excellent candidates for fall planting. In general, plants with USDA cold hardiness ratings of 3, 4 and 5, are the best candidates for fall transplanting in cold winter climates.
Although each plant's needs may vary and some will be more winter-hardy than others, in general about a month before the last fall frost is sufficient in giving the plant enough time to establish itself and take root.
By dividing the plant when it is not flowering, all the plant's energy can go to root and leaf growth. Fall division should take place between early September in the uppermost Piedmont and mid- to late October on the coast. Allow at least four to six weeks before the ground freezes for the plants to become established.
If your perennial blooms in the spring or early summer, it should be transplanted in the fall. If your perennial blooms in the late summer or early fall, transplant it in the spring. Remember that when transplanting in the fall, the perennial needs to be in its new location about six weeks before the first hard freeze.
Divide fall blooming perennials in the spring because
New growth is emerging and it is easier to see what you are doing. Smaller leaves and shoots will not suffer as much damage as full-grown leaves and stems. Plants have stored up energy in their roots that will aid in their recovery.
It's common to think that everything should be chopped down to the ground in the fall, but some perennials actually need their foliage to protect new shoots through the winter. Other varieties offer up important habitat for local wildlife and some perennials provide height and interest through the winter months.
Those flowering bulbs are calling! Don't put down those garden gloves for the year just yet! Believe it or not, October happens to be one of the most fruitful times of year to plant spring-blooming bulbs, hardy vegetables, and shrubs of many varieties.
The date that your ground actually freezes varies from year to year, of course, and some areas won't have frozen ground at all. If you're unsure, mid-November is a safe planting deadline for nearly everyone. - Get everything in the ground before the ground freezes.
Planting in fall allows these plants to establish root systems that they can then bulk up over the winter. Also, in fall, there's usually more rain– which means less maintenance for you.
Some perennial flowers will thrive in areas with low sunlight and come back every year. Astilbes are some of the easiest perennials to grow and will open their plume-like flowers in partial shade. They'll even grow in full shade, although you won't get as many flowers. Hostas are also a good choice for shady spots.
Perennials can be planted any time of year.
By planting them in the fall, plants will have a long time to establish a strong root system before the hot, dry summer months. In fact, the roots are likely to continue to grow as long as the soil temperature is over 50 degrees Farenheit.
Some Sun. Some Shade. So many perennial varieties are vesatile players, thriving in areas with part sun. If the sun in your garden is intense afternoon sun, be sure to provide adequate water or site more sensitive plants in shadier locations.
September is the best month to divide and transplant perennials, but you can still be successful in early October. This is a good time to see the plants that are not healthy and to assess your garden design.
Cutting back perennials in the fall is not only a great way to keep flowerbeds looking neat and tidy through winter, but it also aids greatly in keeping plants vibrant and blooming the following year. Removing spent foliage and blooms helps a plant focus on recharging it's roots and resources.
September is usually best in areas with cooler climates, October is okay for dividing hostas in warmer zones.
2. Perennials and shrubs that are in your zone or one colder can be overwintered in an unheated garage, buried in the ground, or transplanted. 3. Perennials and shrubs in containers will need water through the winter but should not be kept wet.
Some perennials, like hostas, peonies and daylilies, need to be pruned in fall to avoid winter damage. Plants like these should be pruned after the first few frosts in late fall or early winter. Other perennials like mums and coneflowers are better off being pruned in spring just before new growth comes in.
Many gardeners cut back their perennials much too soon. There are nuances specific to certain perennials that dictate whether it is better to cut them back in fall or spring, but the general rule I like to follow is to only cut back perennials that start looking bad in fall.
When To Stop Watering Plants in Fall. When the air and soil temperatures consistently fall below 40 F, it's time to stop watering. The ground can't absorb water once the top few inches freeze. Continue to water your plants up until this point so they're as well-hydrated as possible going into winter.