Many perennials are grown from tiny plugs that reach salable size while growing in a pot. Generally, these container-grown plants are excellent candidates for late summer and fall planting in your garden. It's usually best to divide plants shortly after they have finished flowering.
Late summer is a perfect time to plant perennials and flowering shrubs in many areas. They'll take root during the cool, moist fall weather and be ready to pop into bloom next spring and summer.
Include plenty of late summer flowers in your planting plans to continue the display of colorful blooms well into fall. Often gardens can start to look a little lacklustre later in the summer months when the riot of late spring and early summer choices have faded.
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.
Spring-blooming perennials, especially in the bare root form, 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.
1) Plant before frost. Check your local area's frost estimations and plant perennials at least 6 weeks before the first freeze. 2) Don't fertilize -- fall-planted perennials will be going into winter dormancy in their next stage of life and new growth (encouraged by feeding) will be killed when the first frost comes.
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 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.
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.
Late summer planting
Choose quick-maturing crops. Spinach, lettuce and greens, beets, carrots, peas, and beans can be sown now. Most seeds will readily germinate in the garden now because the soil holds heat well into autumn; warm soil (in the 70°s) is ideal for seed starting, as long as the weather is not too hot.
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.
Dahlias are an obvious choice when it comes to what to plant in August, as they will flower right up to the first frosts and several varieties bring added interest with bronze foliage. You can also rely on long-blooming salvias, astilbes, sunny rudbeckias and gaillardias, asters, sedums and heleniums.
However, there are cultivated plants which are more susceptible to problems if the old foliage and dying stems are left to rot. Diseases can overwinter in dead foliage, as can slugs and other pests. Old stems can also get battered about by fall and winter winds, which will damage the plant's crown and roots.
When to Cut Back Hostas. As a general rule, hostas should be cut back in the late fall. Start with leaves that have wilted or turned brown. Healthy leaves can stay a bit longer to help the roots store needed energy.
Perennials are slow growers at first: They take the first one to three years to establish deep roots and dense foliage. However, once established, they thrive with little maintenance to give your yard beautiful new growth year after year.
Prepare Soil
Add as much organic matter to your planting area as you can. Use things like compost, old leaves, mushroom compost, shredded bark mulch, bark fines or composted manure. Perennials live in the same spot for many years. Adding lots of organic matter creates a base that helps plants thrive.
Perennials are tough plants. They're less fussy about when you plant them or move them. Most perennials can be planted any time from the last winter frost through autumn. When planting or transplanting, dig a hole that's twice as wide and no deeper than the container, then backfill the hole with soil.
It's time for planting fall color, such as mums and asters, as well as sprucing up planter boxes. You also may be surprised to learn that it's the best time of year to plant perennials and shrubs (trees, too!) while plants still have an opportunity to establish their root systems before the ground freezes.
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.