To prevent the disease from returning the following year, we suggest cutting the plants back in the fall and removing any debris – no matter the variety! It will give your plants a clean start next season. *Destroy any foliage with symptoms of powdery mildew and disinfect pruners before trimming other plants.
A perennial with an insect or disease problem should always be pruned in fall, no matter the type. Trim and discard of any infected plant stems to stop an infestation from carrying over into next year's growing season.
Also, do not cut back hardy perennials like garden mums (Chrysanthemum spp.), anise hyssop (Agastache foeniculum), red-hot poker (Kniphofia uvaria), and Montauk daisy (Nipponanthemum nipponicum). Leave the foliage. It's important to protect the root crowns over winter.
While there are benefits to waiting till spring for cleanups, there are still some reasons when fall is best. As a general rule, if you are cutting back in the fall, wait until leaves and stems turn brown — this is a sign the plant is dormant and will not send up any tender, new growth before the first frost.
It's important to cut back foliage in the fall to protect flowering plants from disease and give them a clean start for regrowth as winter starts to turn into spring. However, there are some plants you can keep around through the winter since they benefit wildlife and still offer visual interest for your home.
When to take cuttings. The best time to take softwood cuttings is from mid-spring to early summer. Hardwood cuttings are taken later in the year, from mid-autumn to mid-winter.
A good rule of thumb is that if the plant blooms on new growth, it can be pruned in winter, before the new season's growth begins and after the final bloom of the year. Be careful with spring-blooming shrubs—those usually can't be pruned in winter without damaging the flower buds and ruining the blooming season.
Any gardening expert will tell you, (contrary to what you may believe) that pruning encourages new growth just when the plant is trying to go dormant and new growth doesn't have enough time to harden before the first frost and freezing temperatures hit. Pruning at this time of year will severely weaken the plants.
As the first light frosts begin to hit plants in mid to late fall, the foliage of perennial plants will begin to die back. Once this occurs, it is the ideal time to begin cutting plants back.
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.
Q: When is the best time to cut back in the fall? A: “When they start to look too ratty for you and before the fresh new growth begins,” says Sarah. For plants that are frost-sensitive, wait until after the plants have gone through several hard frosts to ensure they're dormant before cutting back.
Daylilies are best cut back in autumn, once the leaves have had a full growing season on the plant. While there are some evergreen types of daylilies, most are herbaceous, meaning that the leaves die back in the wintertime and sprout anew in the early spring.
Cut stems just below a bud
Using a sharp knife (or pruners) cut just below where a leaf attaches to the stem (the node). Roots grow easiest from this location.
September/October is the ideal time to take cuttings from your favourite strains of tender perennials to increase your stock for next spring or to make sure they live on if the parent plants do not survive the winter.
Hardwood cutting are taken in the dormant season (mid-autumn until late winter) after leaf fall, avoiding periods of severe frost. The ideal time is just after leaf fall or just before bud-burst in spring. Although this type of cutting may be slow to develop roots and shoots, it is usually successful.
Don't shear the branches of spring flowering shrubs (Forsythia, Lilac, New Mexico Privet, Spirea, Flowering Quince, and others). These shrubs produce flowers on last year's wood, so removing old growth will reduce or prevent flowering. These plants should be pruned immediately after they are done blooming.