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Japanese Umbrella Pine & Fungus Gnats

A question about the Japanese umbrella pine; as well as some of the newer controls for fungus gnats!
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

October 18, 2009

Just three shots of our once poor-looking Japanese umbrella pine (Sciadopitys verticillata) growing against the front of the house. No it does not flower like a rose! That’s a rose bud from a climber planted behind the evergreen! Author photos.

Two questions this week.

The first is from Joye who lives in the vicinity of Lake Huron. That could mean she is in zone 6b if she lives in or near Sarnia, or the slightly cooler zone 6a if she is in or near Goderich. North of that she would be in zone 5b, or if she is actually near, say, Parry Sound, would be in zone 5a. Here is her actual question: “I live near Lake Huron and this year I planted a Japanese Umbrella Pine which is lovely. As my house is very exposed to the winds during the winter, I was just researching on the net regarding winter protection when I came across an article that you wrote saying that evergreens get wrapped when they don't necessarily need to. Would this young tree need protection? I would rather be able to look at it, but don't wish to harm it by leaving it exposed.”

Japanese umbrella pine (Sciadopitys verticillata) is generally considered to be hardy only in zones 7, 8 and 9 but occasionally I have heard of people growing one in a well-protected Toronto-area garden. That pretty well rules out Joye’s area (unless she is in Sarnia, but the tree won’t like those winds she mentions)! So, I don’t think she can get away without some reasonable protection for her Japanese umbrella pine.

As an interesting aside, we have two of these evergreens in our street-side garden here, and one was quite a substantial tree until last winter; the other one was smaller, and had a terrible shape which we attempted to correct by planting its main trunk at an angle. Last winter (particularly the abundant snow on the branches) caused a lot of damage to the larger tree, but little to the smaller one. So now, we have a rather poor looking large specimen, and a somewhat reasonable looking smaller tree!

Those problems happening to us here in zone 8 would indicate to me that Joye needs to protect the entire tree by wrapping it with burlap or Arbotex. I would not do that until likely mid-November unless the colder weather hits earlier. The wrapping process is often made easier if the thick stakes on which the burlap (or Arbotex) is wrapped are pounded into the ground earlier in the season, such as now.

Good friend, rose aficionado Doreen Stanton, wrote recently with a common question: “Re: Fungus Gnats; I remember you talking about a method to get rid of these annoying critters but I have forgotten just exactly what to do. Please enlighten me.”

Hi Doreen--it was good to see you out here (in Vancouver) at the International Rose Convention this past June. There is little use in going back to my old recommendations for the control of fungus gnats, which I was giving out on Ontario radio stations in the 80s and 90s--all of those products now seem to be banned. One product you may have, and which is still available is Doktor Doom’s House & Garden Insecticide Spray. I understand the manufacturer is adjusting the labels of many of their products to remove mention of use for outdoors, and just leaving the indoor uses, which would mean if you can find it, it should work for you.

Some other comments about fungus gnats while I am at it. The prime cause for fungus gnats re-occurring is having the soil on the surface of the container always moist. The gnats love that. Let the surface dry out regularly. Some suggest putting a thin mulch of sharp sand on the surface of the soil in each container. They don’t like that.

One sure way to control them is through the addition of Hypoaspis miles a mite that feeds on the fungus gnats. These are available from companies as Natural Insect Control in Stevensville, ON ( ). They are not cheap anywhere, running at about $40 for the smallest quantity.

A novel recommendation is to use Hydrogen peroxide (H2O2): one part 3% H2O2 to five parts water for fungus gnats. This works out to roughly pouring 2 cups of 3% H2O2 into a gallon milk jug and filling with water. This recipe will make the soil fizz and kill any larvae living in the soil. Make sure you use enough to see the solution seep out the bottom of the pot. Be sure to water regularly. The adults will still be alive so you will need to repeat once per week for three weeks and be sure to place yellow sticky card traps horizontally just above the soil. A second recommendation in lieu of the sticky yellow cards is to slice pieces of raw potato and place them on the soil surfaces. These too will indicate the degree of control you have before you really notice more insects.

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