It’s late Spring and I’m already thinking about my gardens Fall blooms (perennials). Why? Because what I do now will give me compact flowering plants in Fall such as Asters, Sedum and Chrysanthemums!
For behold the winter is passed;the rain is over and gone. The flowers appear on the earth, the time of singing come, and the voice of the turtledove is heard in our land.” Song of Solomon 2:11-12
Many late flowering (fall) plants benefit from being cut back before they bloom. These late bloomers will have fuller and more compact habit, less need for staking (if needed) and staggered bloom time if desirable.
Cutting back staggers the blooms giving a longer blooming season. Instead of some of my perennial blooming ALL at once I want to stagger the bloom season to have longer periods of bloom flush and for less staking. This is done by cutting back.
Cutting back autumn-flowering plants for height control is normally done in mid-to-late June in the Midwest, generally when plants are 12 to 16″ tall. Most of the time the plants be be cut back by one-half, but you can prune back by two-thirds or more depending on the plant and what you want.
For mums (as well as many other plants and shrubs), cutting off the top of a stem encourages the plant to grow two stems in its place, which will in turn create more flowers. A plant’s main goal in life is to reproduce. Sure, we find the flowers pretty, but to a plant, flowers are only a means to an end: to create seeds to reproduce.
Asters are one of the first autumn-following plants that the cutting back method can be used. Asters can be pinched (using your fingers) back, but respond well to cutting (using pruners) back too. I cut then back these beauties by 1/2 or 2/3 when the plants are 12-16″ tall is been more effective for me than pinching back.
Cut back the fall-flowering perennials by one-half to two-thirds in early summer for height control and bushier flowering I think to cut mine shorter on outside ends like diagram on the right. Once cut back the Asters flower at 3 feet or so.
There are some Asters that don’t require cutting back, one is Aser tataricus ‘Jin Dai”, only reaches 4’ tall and blooms mid-October. Aster naval-angiae ‘purple dome” is a lower growing aster.
Sedum ‘Autumn Joy’
Sedum Autumn Joy can be pinched for height control but also cut back by one-half in the spring when the plant is 8″ tall (in Midwest this is usually in the first week in June). Plants will have more but smaller flower. If you Sedum is in partial shade will prevent it from flopping.
I think most gardeners think of chrysanthemums with pinching, but cutting back is just as effective. Mums can lack hardiness but mums and pruning go hand in hand. Pinching/cutting back before flowering will create more compact plants, which in turn bloom more numerous with smaller flowers. Natural low growing forms don’t need pruning.
***Pinching/cutting back can prevent blooming if done to late in the summer.
Cold climates (over-wintered) mum pinching/cutting back can be done when plants are 6″ tall (May) and again every 2-3 weeks UNTIL mid-jury. Stopping in mid-July will ensure blooming.
New mums that your’ve planted in Spring should be pinched back a few weeks after planting and again every 2-3 weeks. The cut off date for pinching depends on where you live and type of mum you have. Mums need several weeks to set buds after the final pruning.
Most early season mums, what most garden centers carry, and in gardens North of the mason-dixon line (colder than zone 6) pinching should not be done later than mid-jury. If you live in the midwest, for later blooms in October (which I like) rather than September.
In the South pinching can go as late as mid-august for late-blooming ones.
Sometimes I like to take the easy way since there’s so much to do in the garden! I shear the plants once by one-halfl or two-thirds in early to mid-june. In the south a second shearing ay be necessary for the best results.
***Since mums hardiness is iffy, DO NOT prune mums before winter, leave the the plants up until the next Spring when the threat of all cold weather is over, and prune then. Doing this greatly improves their overwintering survival!
I hope this will help you to have gorgeous fall bloomers in your garden.