Katsura Tree & Re-blooming Iris

A tale of two quite different Katsura trees and why they are so; and a response about re-blooming Iris!
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

November 14, 2010

Above, a shot I took of a reasonably mature Katsura tree in mid-summer, along with two shots showing their typical lovely fall colour. Below two of Chuck Chapman’s re-blooming Iris cultivars, ‘Breakers’ and ‘Red Re-vival’.

Weekly, I often read gardening articles in magazines or newspapers, and that usually includes a quick review of questions asked by readers/viewers to the expert. It is absolutely amazing what I find!

This past week a friend gave me Steve Whysall’s column and “Questions and Answers” from the Vancouver Sun of October 29th last.

Steve doesn’t include the questioners’ names so I cannot address this to the proper person, but here goes any-way!

“I can’t understand why my katsura tree always drops its leaves before the identical tree in my neighbour’s yard does. Mine faces south, his faces west, so both have a sunny exposure.”

Here was Steve’s response: “Cercidiphyllum japonicum (katsura) is notorious for dropping its leaves early. It’s one of my favourite trees. It has such fabulous heart-shaped leaves, a beautiful canopy, and great fall colour, but it can drop leaves earlier than desired.

“The difference between your tree and your neighbour’s is probably in the amount of moisture in the soil in late summer. I suspect your tree is not getting enough water and therefore has a tendency to go into dormancy earlier. Try watering it more regularly in August and September to make sure there is sufficient moisture around the root ball in fall.”

While I support Steve’s recommendations, I do not think they will help the situation. The problem with this tree and many, many others which are grown from seed is very simply “seedling variation”.

I first encountered this situation some 53 years ago in my first year as a student at The Niagara Parks Commission School of Horticulture.

There it was a very large and extensive hedge of European Beech (Fagus sylvatica) which grew all around an area known as the frame-yard. Each spring some of the hedge plants would begin to come into foliage while others would appear completely dormant. In fact, there was often a period of a month or more when different of the trees in the hedge began to put out their leaves. Bert Henning (our English-trained superintendent) always said that was a good example of seedling variation, and that it in fact it manifested itself in a number of different ways with different trees, if they were grown from seed. Some trees, such as Lawson False Cypress (Chamaecyparis lawsoniana), will have perfectly straight branches, while others raised at the same time will have drooping branch tips, and some trees will be a distinct blue-green in colour while others will be a deep green in colour--again from the same batch of seed.

This latter trait is also very noticeable in seedlings of Colorado blue spruce (Picea pungens) which almost always vary from bright green to a light blue needle colour. Nurserymen often select only the bluest of blue seedlings and toss most of the others because the blue coloured mature trees attract a much better price.

What can be done about this? Unfortunately, not much, but if you think about the scenario when originally pur-chasing a tree in the nursery, it is possible to pick a tree that will come out as early as possible in the spring if you choose the one that is actually the farthest out in leaf at the time you make the purchase. Of course, early out in the spring does not guarantee the tree will hold its leaves longer than others in the autumn.

The Katsura tree, as Steve Whysall says, “has such fabulous heart-shaped leaves, a beautiful canopy, and great fall colour.”

Additionally it emits a good strong fragrance of burnt sugar in the fall when it is all coloured up as shown here. It is not necessarily the right tree for hot sunny positions, at least not in its early years. Planted in such locations trees must be kept well irrigated or the thin leaves will burn.

Right now on ICanGarden’s Forum, there is a question from John Perry (zone 5b) about iris, as follows: “I have a white Iris blooming in my customer's front yard... and it is now October 20th! Anybody else have, or seen, an Iris blooming in mid-fall??? Let me know, thanks. John” An additional comment comes from Suzanne (also in zone 5b), “I have a bearded Iris ‘Lenora Pearl’. It didn't bloom in the spring but is going strong now, and has been since the beginning of October. It's gorgeous.”

Re-blooming iris are not new, nor uncommon. Most good iris catalogues note which cultivars are recognized by the American Iris Society as being most likely to re-bloom. That would include highly recognized Canadian Iris hybridizer/grower, Chuck Chapman, who lives and grows near Guelph Ontario. Here is what Chuck says about re-blooming Iris: “Some Iris will bloom after the regular season of bloom. These are called re-bloomers. They most often re-bloom in the fall, but can sometimes bloom earlier and more often. If they have re-bloomed in southern Ontario I have noted this. Other varieties that have been registered as re-blooming are also noted. Warmer areas can have re-bloom on plants that won't re-bloom here. The season can greatly affect the quality and quantity of re-bloom. Extra water and fertilizer in the summer can also encourage re-bloom. The re-bloom is over a long period of time, so don't expect the massed display as in spring.”

You may view all of the Chuck Chapman Iris cultivars that he is offering in 2010 by going to his Website: .

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