Documents: Latest From: Art Drysdale:

Liverwort, Mandevilla, Portugal Laurel & Grass

Have you got liverwort?; a Mandevilla that still is not in bloom; mysterious insects on a honeysuckle, pruning a Portugal laurel hedge; & removing grass for gravel(!),
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 21, 2005

Above, two shots of Portugal laurel (Prunus lusitanica) growing near our old woodshed in Parksville, and below, two shots of our large pond taken on Saturday. Author photos.

Now, here’s a question I have never had nor even thought about previously. It came from Bernice Berber (or perhaps Bernice Diakow). “I enjoy your time and advice seen on Shaw TV. I have a big problem, I have a lot of liverwort in our garden area. I have tried to get rid of it with moss control and have tried to dig it out. But, it grows back faster especially when in very wet conditions. I wonder if you can give me some advice about keeping this under control. Thank you.”

I well remember Mrs. Peters Sr. of Humber Nurseries working diligently removing the liverwort by hand from potted perennials. Unfortunately, there is very little available on the domestic market that will control this pest.

While I am reluctant to recommend remedies such a vinegar, it is literally the only possible solution for liverwort. For commercial operations; and, in Oregon, Washington State and British Columbia liverwort (Marchantia) is an increasingly major concern to growers; the cost of removing it by hand is greater than the sale of the plant in almost all cases. The trade is using, or attempting to use a product called Mogeton, but at present, as far as I know, it is not registered even in the northwest states. Meadowfoam (Limnanthes alba) is an oil seed meal, that after it’s oil has been extracted, can be applied to liverwort with reasonable control, and it is environmentally friendly.

But for domestic use, I think you’re left with vinegar. The suggestion is to dilute the cheapest vinegar one to four with water, and put it in a hand sprayer and spray the liverwort on hot sunny days. If you happen to get some on your plant(s) it should be washed off right away. Another method of preventing liverwort is to control the watering (the least necessary) and if it can be applied from below, that too will help. Reducing the amount of nitrogen and phosphorus fertilizers applied to the soil will also help. And finally, application of a rapidly drying mulch (such as sand) to the surface of the soil in the pots will discourage liverwort.

Mandevilla and Dipladenia questions seem to have been few and far between this year, but here is one from Roly Rees, a friend of my good friend Janet Peaker in Toronto: “My wife was given a Mandevilla plant last year which was producing many flowers. For the winter my wife brought it in the house, cut it back severely and gave it minimum water. After putting it outside this spring it produced many climbing vines and leaves. However to date it has not produced any flowers. Will it ever produce and is it worth keeping?”

In Toronto I used to keep these in a basement cool room. Each may prefer a slightly varied regimen (Dipladenia, for example, prefers a much warmer over-wintering temperature than the similar Mandevilla) but generally my conditions were little or no water and only a couple of 48” fluorescent tubes for light, on for 12-14 hours a day the entire winter.

[By the way, some garden communicators have, in the past, stated that Dipladenia and Mandevilla are one and the same plant. Wrong! However, there is naming confusion and some references refer to Dipladenia under the genus Mandevilla. For practical identification purposes, Dipladenia has rounded oval-shaped smooth foliage similar to lilac, but only about 2/3 the size, whereas Mandevilla has long oval foliage somewhat like the English oak, and it is quite rough and heavily veined.]

The fact that yours has not bloomed yet this year, especially a very hot year (these are tropical plants that love heat) is likely attributable to the fact you did not apply sufficient fertilizer, particularly a type with a high middle number. I suggest you obtain the new Liquid Growth Garden Bloom 2-12-12. Check them out at

Mrs. Dale K. Brunning, yet another ‘Daily Gardener’ viewer wrote inquiring but an unusual pest question: “I have a Lonicera (goldflame honeysuckle) in a plastic pot in our garden against a wooden fence. We have a wooden trellis stuck into the pot and nailed to the fence. The vine started off nicely, but once it started climbing the trellis, something started to eat it. The leaves were eaten from the outside in until there was nothing on the stem. Then the stem would start to shrivel. One night I went out and saw earwigs, so I sprayed them with "Trounce". I also bought earwig bait and put it around the pot and in the pot. But unfortunately something still keeps eating it as soon as it climbs that trellis. The shoots that are coming out from the pot and not touching the trellis are doing just fine and even blooming. It's such a mystery! What do you think it could be and how can I prevent this from happening? I would appreciate any info you might have. Thanks so much for your time and attention."

It would seem your problem is the attacking insect(s) are reaching the honeysuckle from the trellis. I suspect you did not persevere long enough with your treatments of either the Trounce (you should be using it every other day for a couple of weeks I would suggest) or the earwig bait. Then again, it could be slugs--but if that is the case, you should definitely see the slime trails not only on the plant, but also on the trellis and container. Personally, I would get a can of Doktor Doom Residual Insecticide Spray (in the yellow label) and spay the entire trellis, container, and even the soil in the container. It has at least a 60 day residual action and should solve the problem.

Gail also of unknown location, but likely Vancouver Island, wrote, “Could you please send me the recipe for aphid control that had vinegar in it and also the recipe for the control of black spot on roses that used baking soda. Thank you.”

For Gail and others, I cannot recommend any ‘recipe’ that includes vinegar for use on plants (see above re liverwort). It is acetic acid which can ever so easily burn foliage. If you wish something ‘natural’ I would suggest Doktor Doom’s Botanics. As far as black spot on roses, you will not get good control if you use only baking soda. It is good used in combination with Funginex and (if you can still find it) Benlate or Benomyl. When I say in combination, I mean applying Funginex at first sight of the disease, then ten days later applying the Benlate (or other fungicide), and then ten days later again, the baking soda in water. Ten days still later, you begin the cycle all over again. (Keep in mind that it will be even better to apply Funginex in early spring when the foliage first opens. It then works as a preventative.)

Randy McKinnon, apparently a regular viewer of my ‘Daily Gardener’ programme, wrote: “I have a question about trimming back laurel. We have a beautiful Portugal laurel hedge (Prunus lusitanica), but now it is eight ft. high and four ft. wide. I'd like to trim it down to six ft. high and two ft. wide as it's taking over too much of our yard. If I drastically trimmed this there would be just sticks left as in it's present state it only has green on it's outside six inches. What time of year should this be done and would it survive such a drastic trimming? I've included a picture of the hedge as an attachment.”

I would prune it a little less severely (say about 30 cm--one ft.--off the top and two sides) in very early spring, sometime around the end of February. That should allow it to recover easily from new buds for next season. Then if you want to reduce it even further, you could do the same thing the following February. Unfortunately, there was no attachment to your e-mail, bit I could drive over and see the hedge at some point if you wish!

Janeane MacGillivray of Cassidy (just south of Nanaimo here on Vancouver Island) and another viewer of my Shaw ‘Daily Gardener’ segments wrote: “I enjoy your segments on the community channel very much, although I'm not much of a gardener. Can you recommend how to remove a 13' x 23' patch of very uncared-for lawn and replace it with gravel? I live in an RV resort and there is a row of hedge cedars right next to the lawn. The lawn is bounded on three sides by rotting railway ties, which I also want to remove. I have the Pest Doctor coming out next Wednesday to ensure that when I remove the ties, which have ants either living in them, or travelling along them, I can get the ants dealt with at the same time as the ties come up.

“Home Depot recommended that I remove the lawn in squares about 2-4" deep, and then lay commercial grade landscape mat down before I gravel. What do you think? Do you agree with this method, or even better, could you advise me how you would handle the entire project?

First I should not be advising you about the best way to remove a lawn, no matter what size, just to replace it with environmentally-unfriendly gravel! That not so tiny patch of lawn does generate oxygen! If you are convinced that gravel is the only way to go, then I am not fully certain you need to remove the grass physically before applying the gravel. Yes, if you absolutely must have the gravel surface at the same height as what the grass is now, then that would be the best way to go (removing the grass). If it doesn’t matter what the new height of the gravel is, then I would apply RoundUp (Glyphosate) to the entire area and in about seven days the grass (and weeds) will all be dead. Then I would put down at least one layer of the heaviest landscape fabric you can get over the grass, and apply the gravel.

You may wish to punch holes at 15 cm intervals, in a band about 60 cm wide, alongside the hedge arborvitae (cedar), otherwise the hedge plants may suffer from a lack of water and nutrients, easily available to them when the grass was in place. Good Luck; my preferred advice--start taking care of the lawn and have a nice patch of green instead of grey!

As regards the ties and ants, the insects could be simply taken care of with any of the Doktor Doom insecticides, including their Botanics, which is made from the Pyrethrum daisy. No need to call in a pest control company.

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