End of Summer in the Flower Garden

End of Summer in the Flower Garden

As we go into early September, our customers have questions about their flowering plants. Whether it’s how to make their perennial garden look better through the fall, or whether they should cut off browned Hydrangea flowers, we’re ready to help Cape Cod gardens look good through October and beyond. Here are some of the questions people are asking our staff.

1. Should I deadhead my Echinacea as the flowers go by?

If the look of the drying cones annoy you after the petals disappear, by all means clip those spent flowers off. But if you leave them you’ll make the gold finches and other birds happy, since they love to eat the seeds. Usually these cones are fairly attractive as well.

See the yellow bird on the coneflower just to the left of the center of the photo? It’s eating seeds from one of the older cones. The gold finches love Echinacea seed, so leaving the cones after the flower petals fall is good for the birds.

2. Some of the annuals along my front walkway have finished blooming. How can I make this area look good again?

Once annuals are no longer attractive, it’s time to thank them for their service and pull them up. This doesn’t mean that you have to live with a bare border all fall, however. There are many fall annuals that can be placed along your walkway, and the longest lasting are the ornamental cabbages and kales. These will stay attractive until Thanksgiving or beyond, and their vibrant white, pink or purple colors become more vivid as the temperatures drop.

Cabbages and kales become more vividly colored as the temperatures grow colder. You can include other fall annuals such as mums in between them if desired.

3. My Rose of Sharon bloomed for awhile but now the buds aren’t opening. What’s going on with this shrub?

Your Rose of Sharon has finished its bloom time and what you are thinking are un-opened buds are really seed pods. Many people like to cut these off in early September so that the seeds don’t germinate and make hundreds of RoS babies that need to be pulled. You can prune Rose of Sharon and get rid of the seed pods at the same time – just cut those stems back by 12 to 18 inches, and dispose of them. Make sure to cut some stems lower around the outside, moving higher as you go toward the center, in order to keep a full, natural shape on this shrub. Giving it a “flat top” by shearing it straight off the top isn’t a great look for this plant.

Rose of Sharon shrubs have seed pods in late summer and fall that many people mistake for unopened buds. Cut these off and you’ll not only prevent the seedlings next spring, but you’ll also have the shrub shaped and ready to grow fuller next year.

4. My perennial garden has nothing blooming right now. What can I add to this bed that will provide flowers in the late-summer or fall?

There are many great plants that will add fall flower power to your gardens. Consider the following: Perennials including Hardy Hibiscus (dinner plate size flowers in August into September); goldenrod (Solidago species and varieties with yellow flowers that support pollinators); Russian sage (Perovskia – lavender blue flowers from July into October); perennial mums such as Sheffield Pink (Dendranthema varieties, with daisy-like flowers); and perennial asters such as the ‘Woods Blue’ and other colors in that series.

Shrubs that add flowers to your gardens right now include the panicle Hydrangeas (available in many sizes), and blue beard (Caryopteris blue flowers on gray-green foliage).

Hardy Hibiscus are reliable perennials on Cape Cod. Most are in bloom in August, but some flower into September. You can find several colors of flowers, and some have dark foliage as well. In this photo, you can also see the August flowering Joe Pye weed on the left corner, and a Helianthus yellow daisy on the right.

5. My blue Hydrangeas look terrible. Should I them down?

Many people have hydrangeas that look sad after this very hot, dry summer. But if you cut them to the ground right now, you’ll not have any flowers next year. The percentage play is to leave those stems in your landscape through the winter, and wait to see if any of them have life next May. In mid-May, we look at your mophead and lacecap Hydrangea plants and see which stems have small green leaves opening. That’s where the flower will come from, so any cane with green leaves should be left in place. But any stems with no green leaves by the third week in May can be cut out, since those have died either in the summer’s drought or during the winter.

People also ask if they should cut off the brown flowers on their Hydrangea bushes. If those bother you, by all means clip them off, making the cut just below the spent flower. But it’s not necessary to remove them…most of them will turn tan and fall off over the winter, and any remaining will be removed when you clean up the plant in mid-May.

6. What should I be doing for my annuals at this time of year?

Many annuals are at their peak in September, and these can just be enjoyed. Those that don’t require deadheading should be left alone except for watering them when the soil is dry. You don’t need to fertilize annuals after the end of August. Plants that flower better when deadheaded, such as marigolds, Salvia and Zinnias should have their spent flowers clipped off. One way to keep your Zinnias and Dahlias flowering longer is to cut the flowers regularly, and making bouquets is a great way to keep them deadheaded by cutting the flowers before they go by.

Cut bouquets of your late-summer annuals and perennials to keep them flowering longer.

7. Can I collect seeds from my flowering plants to grow more?

Yes, you can collect seeds, especially if you’re adventurous in spirit. Some annuals and perennials are easy to grow from seed, and it’s fun to see what you’ll get when you start these. Often these plants are hybrids, which don’t produce plants or flowers that look the same as those you collected seed from. But that’s part of the enjoyment of growing from home-collected seed. Make sure that the seeds you collect are mature; the pods should not be green but should be turning tan or brown. One option is to put a small, light-weight fabric pouch or bag over the developing seeds so that if the pods open those seeds are kept inside the fabric for you to collect. You can use organza gift bags for this, or cut squares of floating-row-cover (we sell the brand called Harvest Guard) and tie them over the seedpods with a piece of twine.

Asclepias tuberosa, aka butterfly weed, produces seeds that can either be collected or placed on the ground in other areas where you want these plants to grow. These are a good example of a seed that needs winter temperatures to germinate the following spring, so if you collect these, place them on the surface of a pot filled with potting soil, cover it with a piece of fabric or floating row cover, and leave that pot outside where it can go through the winter cold.

8. My perennials and shrubs suffered in the drought this year. What can I do now to help them for next year?

One of the best ways to help any plants right now is to apply an inch or two of compost over the surface of the soil, spreading it over entire perennial gardens or well beyond the drip-line of shrubs and trees. If there is still an inch or two of mulch on the soil, the compost can be put right on top of that, but if the mulch is over 2 inches thick, you might want to rake it away, apply the compost and replace the mulch.

The other thing you can do to improve your flower gardens is to pull the weeds. These plants compete for any available moisture and nutrients, so pulling them will not only make your gardens look better, but will save the resources in your soil for the plants you want to grow.

Crab grass (on the right) and carpet weed (on the left) are two common weeds that thrive in hot, dry weather. The small seedlings on the top of the photo are carpet weed, which laughs at drought. These can be pulled by hand or cut off with a hoe.

For suggestions about success with fall planting, see this UMass fact sheet.

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