Gardening Questions Answered: Astilbe and Zucchini

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This week I have two gardening questions to answer. I will start with a question from Colleen about cleaning up the spent flowers on her perennial Astilbe. The general rule of thumb is to prune down the entire flower stock on a perennial once all the flowers have faded. This keeps the garden looking tidy.

Astilbes are large family of perennials that especially enjoy morning sun but shade from the hottest part of the day. To really thrive they like moist, but well-drained soil. That mean no soggy feet and don’t let them get too drought stressed.

I can give you a good example of how they react to different soil conditions from personal experience in my own gardens. I have a beautiful pink astilbe full of blooms right now in one of my back gardens. This spot does have full morning sun but is in shade during the afternoon. The soil is rich but well drained.  It is a very happy plant that blooms reliability year after year.

However, I do have the exact same variety planted in my front garden. It was gorgeous for the first two years but has slowly decreased in size. What is the difference, you ask? The soil in the front garden is sandier but I fixed that by adding compost and fertilizer. What I can’t fix is the fact that there is a mature maple tree growing just behind that garden. The roots from the large tree fill the soil, suck up moisture and absorb nutrients so much faster than a small perennial can. This competition produced stress that the astilbe just can’t overcome.  It will need to be moved if I don’t want to lose it.

Just as an aside, I do have a few shrubs, Hosta, ornamental grasses, and rudbeckia that are doing ok in that garden. They can compete with the tree roots much better that the astilbe does. 

Astilbes are not perennials that spread by seed, so you can prune off the feathery, spent flower head once the colour fades to brown. I do have a friend that leaves the spent flowers on her plants. In early fall she cuts them back and uses the dried flower stalks as part of her fall arrangements.

If you are growing perennials that spread by seed or that you want to collect seed from, be sure to leave the spent flower stalks on until the seeds mature. This applies to biennials such as hollyhock and foxglove too. You need those seeds to fall into the garden so there are new plants next season.

The other question I have been asked about is why zucchini start to form small fruit but then it turns yellow and withers. This problem is caused by incomplete pollination. Female flowers for squash and cucumbers have undeveloped fruit right behind the flowers. If pollen from the male is not deposited on the female one, the fruit does not develop any further.  

There are two main reasons for problems with their pollination: one is the lack of bees and other insects that move from male flowers to female flowers to complete pollination; the other issue can be if you don’t have male and female flowers open at the same time.

If both flowers are open together, you can collect the stamen from the male flower and rub it on the pistil of the female one to transfer the pollen. You can also use a small soft brush or Q tip to do this task. However, if the male flowers are open and the female ones are not you have a bit of a dilemma.

I did read about a great method to overcome this problem. One gardener suggested you keep a prescription bottle with a Q tip in it right by your plant. As soon as the male flower opens, collect the pollen with the Q tip and seal it in the bottle. Check daily for the female flower to open. Once it does, use the pre-loaded Q tip to complete pollination! I though this was a great solution. I am all set to try this out as I have lots of flower buds of both sexes on my two zucchini plants.  

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About Me

I began my journey in horticulture in 1982 after graduating from the Humber College Landscape Technician program. At that time, I lead a talented crew of landscapers, taught evening courses in horticulture and had my own landscape design and consulting business. Then I ventured into the garden centre world. I’m lucky enough to be leading the friendly and knowledgeable team at New North Greenhouses. 

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New North Greenhouses

719 Airport Road

Sault Ste. Marie, Ontario

P6A 5K6

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