Fall in the Perennial Garden

Fall in the Perennial Garden

October is the perfect time to fall into your perennial garden. The weather is usually lovely on Cape Cod and it’s a good time to get the perennial garden cleaned up and rearranged before next season. Here are some of the things you can be doing in October: 1. Divide and transplant. Have your Hosta grown too large for their location? Have you realized that those taller plants should really be moved to the back of the perennial bed? Or perhaps there are things (Black eyed Susans! Obedient plant!) that have spread so far and wide that they are dominating the garden. Now is a good time to dig, divide and move perennial plants. Just be sure to water them in well once they are moved and keep track of the rainfall; water them once a week if it doesn’t rain, at least through the month of October.  And don’t think that you have to replant every piece of a perennial that you’re editing down…if it’s a plant that spreads agressively you’ll only be creating even more editing and dividing for yourself in the next three years. It’s OK to throw a plant away! 2. Amend soil. Fall is the ideal time to apply an inch of compost or composted manure on your beds. This can be applied right over the reamins of last season’s mulch if there isn’t more than two inches of that remaining. But if the mulch was applied very thickly last spring you’ll want to rake it aside, add the compost and then replace the mulch. In the future, mulch should be spread only an inch to two inches thick. 3. Cut perennials down? This is a matter of taste and convenience. Some people like to have their perennial bed as trimmed and cleaned as possible going into the winter, while others prefer to leave the plants to provide shelter for butterflies, seed for birds, and places for frost and snow to fall. Others want to wait for the spring since they will need to do a spring-cleanup again anyway. There is no one right way here, but in general if a perennial plant looks green and vital in the fall that means that the leaves are still producing energy for the plant. Perennials that are brown, however, can be cut to the ground. 4. Organic fertilizer can be applied to perennial gardens in the fall so that it doesn’t have to be done in the spring. An application of Flower-tone can be spread in October and the nutrients will be available to your plants next season. 5. Leave woody plants in place. Russian sage, lavender, roses and other plants with woody stems should not be cut down at this time of year. Trim the deadwood off these in the spring.

Russian sage is one of the woody plants that should be left untrimmed for the winter. The remains of the Echinacea (purple cone flower) in this garden can either be cleared or left for the birds. Random weeds and self-seeded plants (Verbena bonariensis in this garden) can be pulled at this time of year.

Russian sage is one of the woody plants that should be left untrimmed for the winter. The remains of the Echinacea (purple cone flower) in this garden can either be cleared or left for the birds. Random weeds and self-seeded plants (Verbena bonariensis in this garden) can be pulled at this time of year.

On Sunday October 18th C.L. Fornari will be speaking about perennial gardening at the store – 1 PM to 2:30. Bring a notebook and all your perennial gardening questions! 

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  1. Carla J Roy on October 8, 2015 at 6:24 am

    Can butterfly bushes be cut back in the fall? Hydrangeas?

    • CLFornari on October 8, 2015 at 8:51 am

      Butterfly bush is best cut back in the early spring as the stems store energy that is used for winter survival. If you’re talking about blue hydrangeas they should NEVER be cut down or you’ll have many fewer flowers. Download the handout on our “Resources” page of this website on pruning blue hydrangeas. White “Pee Gee” varieties of hydrangea can be pruned back in the spring.

  2. Jrean schiffmann on October 10, 2015 at 7:43 pm

    You did not mention hydrangeas. I have some tall white hydrangeas that are gorgeous and now turning
    pink and green with the season…they are about l0 feet tall…when do I cut these hardy stems back?

    Thank kyou.

    Jean schiffmann

    • CLFornari on October 11, 2015 at 9:08 am

      I didn’t mention Hydrangeas, Jrean, since they are not perennials but are shrubs. It sounds like you have one of the lovely Hydrangea paniculata varieties. Normally these are left as is through the winter, although if you want to cut off the flowers now and dry them for indoors by all means do so. They also look good used in holiday arrangements aftering giving them a touch of gold spray paint! So cutting off the flowers is optional, and up to what the gardener wants to see in his or her yard. Next spring you can prune these plants in the following manner:
      1. First remove anything that’s obviously dead.
      2. Next, look for branches that are headed into the center of the plant instead of out from the trunk. When you see one of these, follow it back to where it joins another stem and cut it there.
      3. Next look for crossed branches that are rubbing each other and remove one of them in the same method as described above.
      4. The very LAST thing you do is to shorten the remaining branches to the height you want. Unfortunately most people skip right to this step and don’t use pruning to improve the look of the plant but go right for the shortening of all the stems. If you start at #1 and go with the method above you’ll have a MUCH more attractive plant that will also produce larger flowers.

  3. Carol Dubay on October 15, 2015 at 8:45 am

    Is there anything special I should be doing for my knock out roses? They continue to bloom throughout October!!

    • CLFornari on October 15, 2015 at 2:31 pm

      Carol – the best thing for all roses in the fall is to put a heavy layer of composted manure around them. That offers some protection for roots that are near the surface of the soil and amends from the top down next year. Wait and don’t prune until next April. Enjoy!

  4. dc on November 7, 2015 at 10:32 am

    My 3 rose of sharon are gigantic,unwieldly and providing too much shade to my perennial garden. Though i do love their architecture and flowers, I want to cut them off at around 6′ from the ground.What do you think and when should i do it?

    • CLFornari on November 10, 2015 at 4:06 pm

      I think that you can do that but know that they will very quickly grow to be large again – pruning always stimulates growth. If you do drastically cut them, you can do it in the spring. Don’t just chop them off with a flat top – they’ll look unnatural. Cut some of the outer branches lower than 6′ and some in the middle and the center ones the longest so that you retain a nice form as much as possible.

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