THE WAR ON WHITEFLIES
The pests can’t survive Alberta winters, but they can overwinter on indoor plants
Q I had a lot of whitefly in my garden this year and would like to get rid of them for next year. Do whitefly eggs (or adults, for that matter) overwinter outdoors, and if so, what might I do now and/or in the spring to eradicate them for next year? Also, I have herb pots that I put outside during the summer and bring into the house before the first frost. They are currently infested with whitefly and I don’t want the bugs in my house. Would encasing the entire plants and pots in clear plastic bags then spraying inside the bags with horticultural soap a few times be an effective way of getting rid of them? Or do you have better strategies? A Whitefly cannot survive the winters in Alberta, as they do not survive at temperatures below -6 C. However, while the whitefly does not overwinter outdoors it certainly can overwinter in greenhouses. There is a recent paper from Finland that describes this problem of whitefly overwintering in commercial greenhouses, and then in warmer weather they find their way out into gardens. As for the herbs, bagging the plants and spraying with insecticidal soap will likely work. If you want to make certain the plants are free of bugs you can use Doktor Doom Botanics — it contains a natural insecticide (pyrethrin) that is made from chrysanthemums. Keep a watchful eye on your plants next spring, and at the first sign of whitefly spray them with the botanics. Q We have a new garden spot that we used this year that was once an old lawn. The soil packs down very hard, yet water is readily absorbed. It cultivates into a nice workable soil, but it packs down hard as concrete when watered or walked on. What is the best recipe to amend the soil?
A While we have addressed this issue in the past it has been awhile since it was discussed. It sounds like the soil is very tired, and any organic matter in it has been used up. The best thing you can do to help the soil is adding more organic matter, in the form of either rotted manure or compost. Stay away from peat moss, as this product is naturally acidic and can affect the pH level of the soil. There are several ways to add the organic matter. The first way is to dig it in by hand. Spread
the organic matter over the top of the bed to a minimum depth of two inches — more is always better when it comes to adding organic matter — and then turn the soil over using a spade. The best time to do this would be in the fall. This will allow the matter to break down over the winter and spring. Once spring arrives, rake the entire area very well. The other method is to spread the matter on top of the soil and then rototill it into the bed. This method is beneficial because the tiller will break the organic matter up very well and incorporate it into the soil better than just hand digging will. One negative consequence is that the tiller can compact the soil. This can happen in the area where the tines of the tiller reach the bottom of the bed. The best way to avoid this soil compaction is to make one or two passes fairly quickly and let it set for the winter. Q My kids give me mums for Mother’s Day every year. I plant them outside and they grow well, but they never bloom again. The mums even show up again the following spring and grow about four times the size they were the year before, but they still don’t bloom. Is there anything I can do to make them bloom? A Florist chrysanthemums are not hardy for re-blooming outdoors in our area. While they may survive, our climate is too cold for them to form flower buds, so I’m afraid you will only be able to enjoy them indoors while they are blooming. These plants are grown to be enjoyed and then thrown away.
Gerald Filipski is a member of the Garden Writers Association of America. Email your questions to filipskigerald@gmail.com. He is the author of Just Ask Jerry. To read previous columns, go to edmontonjournal.com/filipski