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Dividing Perennials, Insect Control & Hydrangeas

When is the best time to divide and re-plant perennials such as Hosta and daylilies; clipping perennial flower heads; a little on insect control and planting Hydrangeas now. Plus, planting annual and vegetables this month.
by Art Drysdale
by Art Drysdale


Art Drysdale, a life-long resident of Toronto and a horticulturist well known all across Canada, is now a resident of Parksville, British Columbia on Vancouver Island, just north of Nanaimo. He has reno-vated an old home and has a new garden there. His radio gardening vignettes are heard in south-western Ontario over radio station Easy 101 FM out of Tillsonburg at 2 PM weekdays.

Art also has his own website at

August 12, 2007

Above, two shots of some daylilies in our garden in Parksville, showing Hemerocallis ‘Apricot Sparkles’ and a wider shot with Shasta daisies and a poppy. Author photos. Below, the the rare and not-well-known Bupleurum. Photo by Esmeralda Farms.

Sandy Ferris of Scarborough wrote me on Monday this week with a good general question: “About 7 weeks ago I was listening to your show and called in with a question. The screener tried in vain to connect me to you but was having technical difficulties. I could hear you but you could not hear me. Approximately 15 minutes later the screen-er asked me for my address etc. and said they still had a technical problem but as a gesture they would send a prod-uct package in the mail. To date I have not received anything.

“My question was, when can I prune my perennials to give some to other family members such as daylilies, Hosta etc. I enjoy your program but unfortunately cannot listen to it every week and therefore may have missed a program re-lating to this. Could you kindly email the answer at your earliest convenience?”

My apologies that due to a technical glitch at the radio station end, for two weeks, as I recall, I was unable to hear the callers. I also have to apologize for not sending a BioTLC fertilizer sample, which my radio station operator promised. He was not aware that we had stopped sending such samples. I have now written Brian Costello at BioTLC and he will likely send her something.

As to perennials, for some reason the transplanting and dividing of perennials is a mystery to many gardeners. Maybe I should begin by telling you that my own policy on these always has been in almost all cases, to divide and transplant whenever it becomes obvious, for whatever reason, that it is needed, In the case of the two plants you have named there should be no problem.

Right now is a terrific time to be dividing and replanting Iris, peonies and daylilies, and in fact the growers of these such as Chuck Chapman Iris near Guelph and We’re In The Hayfield Now daylily farm in Orono are shipping plants at this time of year as it is the ideal planting time.

That is not to say that you cannot do this at many other times through the growing season. In fact, the only time when it is best to resist dividing and moving perennials is when the plant(s) are in bud or flower. Early spring is a great time to work on perennials, as is the autumn for most genera.

While responding to Sandy, and since she used the word “prune’, I should also add that again for most perennials, it is best to prune off the old flower heads before they turn into seed heads. The only exception to this is if you know the perennial is capable of re-growing from seed, and you wish them to multiply that way. Columbine (Aquilegia), lungwort (Pulmonaria) and many, many lilies are examples. On the other hand, many plants that are excellent perennials a way over produce from seeds and in such cases it is important to cut off the seed heads before seeds ripen. A good example of this would be goldenrod (Solidago).

Also this week, Madge Veitch of Innisfill, Ontario wrote, “Something is eating my potato vines planted in planters (I have some in hanging baskets - they are fine) they are covered in little round holes - I have tried trounce but no success - can you help?”

Tough to identify insects this way but regardless of what they are, I think you are not spraying them often enough. I would say use something just a little stronger, for example Doktor Doom House & Garden Insecticide which contains .25% Permethrin. It is completely safe, and the label does not require a poison symbol on it. But, the important thing is to spray every couple of days for the first two weeks, and you’ll likely see the new leaves are free of the holes. By the way, I would also spray the plants in the hanging baskets as well, in case you chase them further up when you begin spraying.

And finally this week, as far as questions, Betty Hilke, from whom I’ve heard before (she lives in Qualicum Bay--further up the Island Highway from Qualicum Beach which is just above us here in Parksville) asked when was a good time to plant a Hydrangea.

Anytime now would be good, but I would make sure you check all the nurseries/garden centres in the area, because many are offering some good bargains on shrubs now. And, many will still be in bloom, hence you can make a good decision as to what colour you wish.

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While writing about things to do in the garden now in early to mid August, let me remind you that there is still plenty of time to sow some seeds--both flowers and vegetables. Particularly, August is a time to sow seeds for fall salads. I'm thinking about all of the leaf and root crops, not the fruiting crops: lettuce, endive, escarole, radicchio and other chicories, spinach, chard, arugula, cress, mustard, kale, radishes, and turnips. Other vegetables you should likely consider re-sowing or sowing a first crop are: beets, broccoli, cabbage, Chinese cabbage, carrots, fennel, greens, col-lards, kohlrabi, lettuce, onion (bunching and mini), peas, radicchio, radishes, spinach, and squash (summer).

If you don’t have much space, you can obtain a single pack of seed for a combo of six different lettuce varieties and sow them in a container on a sunny deck or patio. Park Seeds’ Master Chef Blend is just US$1.75, but order them soon! You should be picking several different lettuce types in just over two months.

What about annual flowers you might ask! Yes, there is a reasonable list you can still seed and have some results be-fore the snow flies. For example, Agrostemma, asters, bupleurum, calendula, celosia, centaurea, coreopsis, cosmos, gypsophila, kale (ornamental), marigold, morning glory, nasturtium, nigella, phlox, and reseda. In case you were wondering about “Bupleurum”, I did check and it has a couple of uses, including by floral designers to bulk up their arrangements. It is also a very popular as a Chinese herb used in ever so many tonics--in other words good for almost anything that ails!


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