Documents: Garden Design:

A Little More on Those Horrible Fungus Gnats; & Looking Back at Canada’s Centennial Tree
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

February 5, 2012

These nice, even ‘Royalty’ crabapples are growing in the Braun Nursery in Mount Hope Ontario. Photo courtesy of the nursery and its owner, Peter Braun.

This week it’s back to Caroline Onishenko in Edmonton and her question of last week about fungus gnats. Let’s start with her response to my item:

“Thank you very much for your reply regarding these annoying pests. I have already bought a can of Doktor Doom House & Garden Insecticide Spray and have sprayed 2 of my plants – on the soil and then worked it in with my hands for the top few inches. Already, I can see an enormous reduction in the flies. If you would be so kind to answer two questions:

“I had held off watering my plants for about two weeks as this was also suggested as helpful in eliminating the gnats – if I water now, will the insecticide go through the soil to the roots and do damage to the plant?

“Also, in future when I buy potting soil, if I were to spread it on a baking pan, and heat to a high temperature in the oven, would it kill these pests before I use the soil? If this is not the answer to this problem, what would you suggest to ensure the potting soil I purchase does not contain these pests?

“Again, thank you very much for your help. I have been to Parksville and know it to be a lovely area – I hope you are enjoying your new home there.”

First, regarding watering, it is definitely true that by reducing watering, you will reduce the presence of fungus gnats. You should assure that about the top centimetre (half-inch) of soil in the pots is absolutely dry before you water your plants. And, while watering will to some extent, carry the insecticide down deeper into the soil, it will not be harmful to the plants’ roots.

Now, as to potting soil, that is where the real problem is. The sole answer is to buy only sterilized potting soils. These are generally sold for seed starting and can be considerably more expensive. The only other solution is to do as you suggested—sterilize the potting soil yourself. But, before you decide to do that you should know that the old method of sterilizing soil was to heat it in a conventional oven so the temperature of the soil reached 180o F and remained there 30 minutes. The problem is the heating creates a strong stench throughout the home.

I've had inquiries previously as to whether you can sterilize soil in a microwave oven. Yes you can! Here's the correct procedure. Do about 4 to 5 kilos (10 lb.) of soil at a time. It should be moist and crumbly, but not oozing water. If it is dry enough to plant in, it’s dry enough to microwave. Put the soil in a plastic bag (polypropylene bags used for baking are less likely to burst than common polyethylene). Twist the top of the bag slightly, but don’t seal--it might explode as steam builds up. Alternatively, use a loosely covered bowl.

With oven at full power, heating for seven minutes will kill most diseases and insects. If you are seriously concerned with damping-off disease killing young seedlings, or have had problems with other soil borne diseases or insects such as fungus gnats, extend, or even double the heating time. The high water content and myriad of pore spaces in compost or leaf mould will considerably slow the heating process if they're included in the mix. After sterilization, let the soil stand uncovered until cool and store in sealed containers. Clean the oven thoroughly, particularly the door seal, after use. So, again Caroline—Good Luck!

* * *

This week, on Wednesday, another question which I’ve not had before (unusual!) rolled in from my friends Sheila and Peter Keeping of the Durham area east of Toronto. It read thus:

“Would you be able to throw any light on this tree? It was before our time.”

Following this short request were two other e-mails, which, when I got down to the bottom of them was the ac-tual question from Mary King of Harley Ontario (8 Ks south of Hwy. 403 on Hwy. 25):

“I have been doing some research on the internet and from a [Ontario Horticulture Association] website [and] I now know that the Canadian Centennial Tree is a Royalty Crab. I would like some further information about these trees.

“How long they will last? How to take care of them? What to do if they are too far gone? Can I graft a piece of the tree to plant another one? Would I be able to move it to another place on my property?

“The reason for all these questions is we bought this property and this tree was planted here in 1967 and I would dearly love to keep it if I can. Any and all information you can give me will be greatly appreciated.”

As it happens I am quite familiar with the ‘Royalty’ crabapple, since I was chief horticulturist for Sheridan Nurseries when it was introduced through the Canadian Nursery Trades for the 1967 Canadian Centennial. Now, I have written in various items on previously about the huge controversy that came up over the ‘Canadian Centennial’ rose introduced by Mr. Jack G. McIntyre and the not quite so competitive (from a marketing point-of-view) ‘Miss Canada’ introduced by the Canadian Nursery Trades at the same time.

Well, the introduction of the ‘Royalty’ crabapple was almost as controversial, but in a different way. The tree was from Saskatchewan so everyone knew it would be hardy (to zone 2). It had/has beautiful red-turning-to-purple foliage all summer (superior to such trees as the purple plum [Prunus cerasifera, or known then as Prunus pissardi) and was hardier, and the foliage had a beautiful colour change in autumn to orange/bronze.

But, and it was indeed a big “but”, at the time of its introduction to nurseries across Canada so that it could be grown on in order to have a large number of reasonably-sized trees available in the Centennial year, it had never flowered so the colour, or even whether or not it would flower (some pessimistic folks said it would not!) was unknown. The question became--how can we promote and sell a “flowering tree” that has never flowered? However, everyone had sigh of relief in the spring of 1966 when the trees flowered with dark pink flowers.

The one problem the tree had, and still very much has, is it is subject to diseases—particularly Fire Blight (Erwinia amylovora), with which all members of the Rosaceae family can become infected. However, some trees are far worse than others. And, Fire Blight is far more a problem on the Prairies than it is say in Ontario, Quebec and British Columbia. It is for that reason that in the stock lists of most Prairie nurseries, such as Dutch Growers Garden Centre in Saskatoon (Harry Van Duyvendyke the founder is an old friend of mine) do not list ‘Royalty’ crabapple.

As to your questions, most crabapples can be expected to last in the range of 40 to 50 years, provided it is not hit with the dreaded fire blight which will generally kill it the year it hits. They generally form a rounded tree, and usually would not be expected to exceed seven or eight metres in height (20 ft.). They do prefer a sunny growing location, but have few other ‘demands’. They do require some pruning, perhaps annually, which will help slow its growth and thus help prevent fire blight. It is not fussy as to soil, except that I would not recommend it be planted into a consistently damp location.

Any tree that is “too far gone” should be removed before it dies as live trees are usually less expensive to re-move than dry, dead ones.

Following general arboricultural suggestions, a part of your old tree could be either budded onto another root-stock, or part of your tree (scions) could be grafted onto a section of another larger compatible cultivar.

The moving of large trees is done all the time, but you would need to take into consideration how many years of life the tree likely has left before investing in such a move.

I hope the foregoing ideas will help you make your decision as to what route to follow.

* * *

Next week, look for my review and comments on the Northwest Flower and Garden Show in Seattle—entitled “A Floral Symphony”. I hope nearby readers will get to see it as well—it runs February 8 - 12.  

  • New Eden
  • Kids Garden
  • Plant a Row Grow a Row