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Scree Gardens, Vegetable Maggots & Sweet Potatoes

Here I go again on Scree gardens; onion and other root vegetable maggots and their control; and the availability and growing of sweetpotatoes in Canada!
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

May 11, 2008

Above, three shots of two of Keith Squire’s scree gardens taken just about a year ago now. Author photos. Below, remay cloth being used to protect growing crops courtesy of; a good sweetpotato sliced courtesy; sweetpotatoes growing in late summer (August) courtesy of

Last Sunday, Judy Fountain of Uxbridge Ontario wrote with the following comment and question: “Unfortunately I just tuned into your garden show as it was nearing the end of the programme. There was a gentleman talking (I believe) about a topsoil that prevents weeds. His nursery was mentioned as well but unfortunately I have forgotten that. I thought, from the little bit of information that I did glean, the topsoil was for grass. We are currently looking for something to curtail the weed situation without turning to chemicals which we understand was officially banned during our recent vacation in Myrtle Beach. I would be most grateful if you could provide me with the name of the nursery and your guest speaker as we are anxious to feed our winter damaged lawn. Thank you so much in advance for your help.”

Judy, and others, I first have to tell you that when ever Keith Squires of The Country Squires Garden in Campbellville Ontario and I discuss Scree Gardens, there are always people who don’t hear enough to understand just what we talked about. You are no exception.

Scree Gardens are those that are made solely of Pit Run “A” Gravel and the plants are placed directly in the gravel without any soil. Most plants do well in these situations, and once they are established, literally no watering needs to be done, and, the point you heard, there are few weeds that come up because the gravel is usually clean of weed seeds when it is delivered.

As regards a lawn, scree gardens have little to do with grass. You are not quite correct, in that lawn care chemicals have not yet been banned, but will be. I would suggest using a good weed control chemical about now while they are still legal and available. There is a new type of selective weed control that will be becoming available, but not until next year (2009) at least. A few details about it may be found in my article of last week (May 4), also on this site.

Back a bit, on May Day, Darlene Gleim of unknown location (quite possibly here in B.C.) wrote with another common question: “I have a terrible problem with root maggots in my food garden beds. My radishes, onions, turnips & other root vegetables get tunnels of maggots in them every year. Do you have any suggestions other than using granular Diazinon, which I would prefer not to use? Can Doktor Doom be used in rows along with seeds when planting?”

Basically, unless you have stored a quantity of granular Diazinon, you are out of luck as it has been removed from the market, at least for domestic use. I have dealt with this question on a couple of occasions last year, so will repeat that advice for you here.

There simply is not an easy-to-use substitute. Let me explain first how these pests ‘operate’. That may help.

Shiny-green, yellow-headed flies (6 mm) lay eggs on soil surface near plants in late spring, early summer. The emerging larvae (maggots) dig down and attack tender roots. They pupate in the soil and emerge as adults in August or September. These mate and lay eggs which hatch into larvae that over-winter in the soil or in the roots (they are found in stored carrots).

The one characteristic these pests have in common is that the initial contact is made by the adult fly. The ‘old’ idea of putting the granular Diazinon into the soil was to get it into the area where the roots would develop and thus it would kill the larvae before they could do any damage to the roots.

One of the prime methods of preventing attack is moving the plantings of these vegetables to entirely different sections of the garden each year. Then, there are no lingering larvae to infest the young plants. However, that is often virtually impossible in small home gardens.

Now, there may still be an opportunity to use a similar method to that of the old granular Diazinon, only now using Dotor Doom House and Garden Insect Spray which contains 0.25% Permethrin, the water based chemical insecticide that was formulated as a copy of the naturally-occurring Pyrethrins. This product, like all Doktor Doom products, does not bear any ‘Poison symbol’ on its label and is safe to use.

In talking with the good Doktor Grigg, he told me that after checking various university Websites, he is suggesting that since the larvae mature on the soil surface at the base of the planted crops, there is a good possibility that Doktor Doom House & Garden Spray could take the place of the granular Diazinon. Apply the aerosol spray to the soil before planting the rows and treat the areas around the plant stems immediately after planting. “Given we have a residual in the soil and that the plants are treated early in planting--this should last for up to a month and it should work.”

Doktor Grigg emphasizes that you should be certain “to make the application to dry soil and stir it in after it is applied--and immediately follow up with planting (or seeding) and then apply at the base of the plants once they are in the ground, or if seeding, as soon as the young plants emerge.

You can be sure that this method has been tried by many last season but I have had no reports aye or nay!

Now to some other ‘solutions’. Just as planting in areas ‘clean’ of larvae from previous years is helpful, it is likewise important to eliminate host-weeds like wild carrots (Queen Anne's Lace), lamb’s-quarters (Chenopodium album), wild parsnips and hemlock in the neighbourhood. Also, seeding early (mid-March) and harvesting in May or delaying seeding until June and harvesting early August will help due to the life cycles of these insects.

Another control that I have learned has been used in the past is to plant carrot rows between rows of leeks, sage or rosemary. These latter will repel the carrot rust fly. Also, in talking with Gord Nickel of the ‘Get Up and Grow’ TV programme, he recalls his father hanging cloths that were dipped in kerosene on sticks along the rows of the vulnerable vegetables. We have no experience with this, but I can well understand it working in much the same way as do the mentioned herbs.

Finally, perhaps the second-best solution, after the use of the Doktor Doom aerosol insecticide, is row covers. My friend Tom Thomson at Humber Nurseries has been suggesting the use of these for several years, because they are an economical, relatively simple, non-chemical solution to insect problems. The material used should be fine cheese cloth or muslin (possibly called remay-cloth in the U.S.) and it should be applied over each row immediately after seeding, or planting of young transplants. The width of each row cover should be about 45 - 60 cm (18 - 24”) and the edges should be held down with soil to prevent the insects getting into the planted area. Ideally, each row cover should be slightly hooped up using flexible branches or the like (so that there is a clearance of about 15 cm in at the row centre to allow the plants to grow), but even if the material is flat on the ground with lots of spare material to allow the young plants to push it up as they grow, the row covers should work well. They can be removed after about three or four weeks. Keep in mind that cheesecloth does allow penetration of full light and rain or irrigation.

By the way, something I did not mention last year is that if you cannot find (or afford) remay cloth, you could use old sheer window curtains!

Just on Thursday of this week, Denise of Courtenay here on Vancouver Island wrote this short note: “Hi I am looking to grow sweet potatoes - do you sell slips, the article you wrote indicates you do but not how to purchase them. I am in Courtenay and would like to get some.”

Well, Denise, I am unsure to which article you refer, but I hope I never conveyed that I have sweetpotato slips for sale. Likely the recommendation I made was to obtain sweetpotato plants (slips) from Mapple Farm in Weldon, New Brunswick. Greg Wingate the owner has done a great deal of work on growing sweetpotatoes and lists over a half dozen varying cultivars and is testing others. He also grows and sells a number of other plants including Jerusalem artichokes (Helianthus tuberosus), Chinese artichokes (Stachys affinis) and Horseradish (Armoracia rusticana) as well as “uncommonly good garden seed” of: unusual and distinctive tomatoes, Chufa nuts (Cyperus esculentus sativa), Banana squash (Cucurbita maxima), Black zucchini (Cucurbita pepo), Parade cucumber (Cucumis sativus), and two new items, Nutmeg melon (Cucurbita melo) and Shosaku gobo (Arctium lappa). He also offers “uncommonly good onion family stock!”

You still have time to obtain sweetpotato slips from him, provided he is not sold out. I would suggest contacting him by e-mail: . Gregg also offers Ken Allan’s soft cover Sweetpotato book at $20

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