As the gardening season nears the end and the flowers have faded, most perennials get a little straggly looking and not so pretty anymore. Some perennials and many herbaceous plants like to be cut down in the fall due to mildew and other issues in rainy areas.
There are also some perennials that prefer to be cut down in the spring because they use their dead summer foliage for winter protection usually for the crown of the plant.
Here is a list of common perennials to cut down in the spring.
There are many other plants that are perennial in other zone areas that are not listed here. This just a basic list of the more common ones you’ll likely have or see in the stores in Climate Zone 7-8.
Achillea (Yarrow) – Cut back flower stalks as they fade and leave the foliage on
Bearded Iris – Cut back when stalks turn yellow
Bee Balm (Monarda) – Cut back when mildew becomes apparent, new growth can stay. You cannot harm this plant it’s very tough so chop it down to control mildew. This is a vigorous grower and I recommend a container for this one.
Blanket Flower – This plant responds with more vigour when cut back
Brunnera – The leaves turn black and unattractive, cut back once they start to do that. If you live in a rainy area you may choose to leave the leaves on top of the pot or plant itself to protect the crown. May not survive a lot of rain.
Butterfly Bush (Buddleia) – Clip off just the faded flower heads in fall (it’s a self-seeder and invasive). If you prune this one completely the fall you greatly increase the chances of it dying over the winter. Leave it as is until signs of new growth show in the early spring and then cut it back to 8″ to 12″ tall. Zone 6-9
Catmint (Nepeta) – Cut back this one anytime you want, it’s a very tough plant and will regrow from anything you do to it.
Centurea – Cut back flower stalks as they fade, leave the leaves on to protect the crown of the plant.
Columbine (Aquilegia) – Cut back as mildew forms, watch for little green worms munching on your Columbine in the wet season
Crocosmia – Cut back when it turns yellow
Day Lily (Hemerocallis) – Cut back to a few inches tall once it turns yellow
False Sunflower (Helianthus) – Cut back to the ground after flowers are done
Helenium – Prone to mildew, cut down and destroy the foliage, do not compost
Hollyhock (Malva Alcea) – Also known as a Plume Poppy This is an enthusiastic self seeder and must be cut down in fall when flowers are done to avoid them sprouting up everywhere
Hosta – The leaves turn yellow as it takes the nutrients back to the roots from the leaves. Once they are completely yellow they should be cut down to about 1″. In dry areas the leaves are crispy and yellow, in rainy areas they turn yellow and mushy.
Lily (Oriental and Asiatic) – Leave the stalks standing for as long as possible after the flowers fall off. They will eventually turn yellow.
The longer you allow them time to turn yellow the larger and more robust your blooms will be next summer.
Lily (Tiger) – Very similar to the other lilies above, leave the stalks standing until they turn yellow. You might find at the base of each leaf right at the stem is a little black ball. This is a Bulbil aka a lily seed, baby tiger lily.
Leave them on the stalk until they are quite large then carefully pull them off (you may see tiny white roots) and gently plant them in a seed starting tray or the ground. You can create unlimited tiger lilies.
Penstemon – Cut back at the end of summer when blooms fade, tall fronds will allow too much water to stay at the crown and cause crown rot
Peony – Foliage is extremely prone to mildew and should be cut down
Phlox Paniculata – This is prone to powdery mildew and should be cut down and the foliage destroyed as flowers fade.
Salvia – Cut back to new basal shoots
Soloman’s Seal (Polygonatum)- This plant becomes yellow like a Hosta in the fall and should be cut down in the same manner.
Speedwell (Veronica) – Trim back to the ground when blooms fade