Tomatoes, Potatoes, Algae & Mandevilla Vines

More Blossom End Rot problems with tomatoes; how to plant ornamental potato tubers; what to do about algae in ornamental ponds and growing a Mandevilla vine outdoors!
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 25, 2008

Above, a shot of a pond completely taken over by algae, and one of a part of my smaller pond at just about this time last year. Author photos. Below, a couple of the Sun Parasol Mandevillas growing in a cocoa-fibre-lined basket. The vines will be allowed to grow up the sides of the trellis. Photo by Norman Winter, Mississippi State University.

Alan Boyle, of unknown location, wrote last Monday, “We have a problem that perhaps you could shed some light upon.

“We have a small garden plot and for the past decade have planted primarily tomatoes and some beans in this plot.

“Because of the small size of the plot it is nearly impossible to "rotate" the crop and the past 2 or 3 years we've experienced smaller yields, and perhaps 20% of the planting (12 plants experience leaf curl and very diminished numbers of fruit and an early demise of the plant. However some of the remaining plants grow what I would consider excess foliage.

“I do try to "sucker" the plants every week or so and have even resorted to removal of some of the extra foliage - from the bottom. We normally use plants of the "Big Boy" strain and support them in metal cages. Watering is not a problem as I have water at the garden's side.

“A couple of years back when first exploring this problem I was told I should use "lime" under and around the plantings - was supplied with a granular product. Since then that man is no longer at the local nursery and I've lost all records. No one seems to have a definitive answer as we've been told the plants needed calcium or lime or heaven knows what else and to no avail.

“I turn over the soil each year, add some peat and extra black soils into the mix.

“The only outside problem is the neighbour who has a nearby fence line of Cedars and Lilacs and I do uproot red roots when digging up the spring soil.

“It is fast coming to the tomato planting time (early June according to you) and we would like to solve this problem short of attempting to relocate the entire plot somewhere else on the property. We would appreciate the help you can provide.”

Your final comment above is really the solution you should be seriously considering. Nothing else you do will be as effective as relocating the tomato plot. But, if you do not wish to do that then Horticultural Lime (the prilled or pelletized form is best) applied to the entire plot and worked into the top 5 cm of the soil at the recommended rate is the next best thing. Once the plants are growing, if you should notice some black bottoms on individual fruit, that is blossom end rot, and the cause is replanting in the same area year after year. You can try to address it by applying powdered milk product to the soil around the plants.

The other idea you should consider is to plant different cultivars (varieties) of plants. In other words, if you have been using ‘Big Boy’, switch to something else like, say, ‘Early Girl’. When buying your plants source them at a good nursery location that has a multitude of cultivars, and that indicates to which diseases and viruses each particular variety is resistant. If that information is not available with the plants, try to check it out in a good seed catalogue such as Stokes before proceeding with your purchase. The more disease resistance a cultivar has, the better for you since they are being planted in the same location as previous years.

Those are the only suggestions I can make for you. I would add however, the business of removing pieces of foliage is an old wives tale and often does more harm than good. Even removing the suckers is not always a great advantage. The plants need the foliage they produce to manufacture the food that will produce better fruit.

Last Sunday after our Chat session had ended, Gail W. from either Oshawa or Toronto, typed in the following question: “I have saved decorative green potato tubers from last year. They are huge. Do I cut them up and plant them to get new plants?”

Yes, Gail, just like the eating potatoes, “seed potatoes” either as sold in boxes in garden centres, or as cut up by gardeners, are just the potato tubers from the previous year cut up to have at least one set of viable “eyes”. No rush getting them in until the weather warms again.

On Tuesday last week I received two inquiries on the same subject--algae in ornamental ponds. They came as a result of one my vignettes on AM740 in Toronto (and other southwestern Ontario radio stations such as FM101 out of Tillsonburg and CD 98.9 out of Simcoe). Here’s the one from Joe Halajian: “have a small decorative fish pond, 5 x 5' x average of 8 to 14" deep. I manage to keep the fish alive over the winter by using a 10" diameter disk heater and a bubbler. They all survive the winter. There was a huge algae build-up and in the spring I removed all the flagstones lining the sides and bottom of the pool and scraped the algae off. I use barley pellets in a nylon stocking to keep the water clear plus a pond balance material. My wife heard your show last weekend regarding this type of pool and I would appreciate a reference where I could hear the show again or read about the recommendations you made. What did the peat moss in the sock replace?”

The other one came from Jim Macgregor, and he mentioned having used Sera Pond Clear, but that it had not worked effectively; and he further asked what the “bundles of…” I mentioned in the vignette.

I responded by sending the contents of two of my radio vignettes that had prompted the inquiries. “Algae can take one of three different forms but the most common is filamentous, resembling green angel hair attached to the sides of the pond and any plant containers in the pond. There are several ways to control algae, but the ideal solution is a combination of many preventatives. The first is never to drain the pond and start all over again with fresh tap water. That so-called solution will just give you a larger problem. The second important point is to have at least three bunches of oxygenating plants per square metre of water surface. Oxygenating plants are economically available from garden centres and specialized water gardening outlets. These plants should be potted, and set on the bottom of your pond. The third important point is to have at least 70 percent of the water surface of your pond covered with water lily foliage. Though water lilies need full sun, by shading the water with abundant water lily foliage, algae growth will be severely curtailed.

Also, there are now several chemicals that will get rid of algae, with absolutely no affect on either fish or the aquatic plants. One of the prime ones is Sera’s Pond Clear, which Jim Macgregor mentioned using. I think likely Jim’s problem was that he didn’t use enough, and perhaps he did not know the approximate volume of water in his pond in order to know just how much to use. He also likely should have repeated the treatment a few weeks later.

Once the season is advancing, if algae should become a problem again, the addition of Peat Moss tightly stuffed into a panty hose, each six weeks will reduce the presence of algae. One of the benefits of using Peat is that it tends to acidify the water, which in most of our ornamental ponds today becomes far too alkaline. If the water is too alkaline, it can be harmful to fish, and not nearly as good an environment for the water plants as water that is either neutral (pH 7) or slightly acid. A kit that tests the acidity as well as the nitrite content of your pool will also be found to be extremely valuable. Again, your local garden centre specializing in pond products is the source of these items.

Finally this week, Sonya Hicke of nearby French Creek (between Parksville and Qualicum Beach) wrote on Friday with this question (the answer to which applies to gardeners in most of Canada): “I live in French Creek and am considering purchasing a Mandevilla vine this year for our arbor ..... my husband absolutely loves them. However, since they are not winter hardy would like to know: can I keep them in the original pot or should I re-pot into a larger one and stand that pot beside the arbor and let it climb all summer? What do I do over the winter? Thank you so very much for your reply.”

Depending on the size of the pot the Mandevilla vine comes in, yes, I would definitely put it in one that is at least five gallons. For the winter you can cut it back severely, and bring it into a cold room where it will not freeze. For example, a garage could be fine, as long as you put it back outside when it starts to shoot out the following spring, possibly as early as February in French Creek. If below-freezing temps are expected after it is back outside, just bring it indoors for the cold nights.

One of the latest crazes in Mandevillas is the Sun Parasol series with several distinct colours. They replace the previously most popular cultivar ‘Mrs. Alice du Pont’.

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