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Miss Floribunda: Water roses at the roots to stop black-spot disease

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Posted on: September 10, 2013

Dear Miss Floribunda,

My roses haven’t had a good summer. The frequent light rain has resulted in a lot of black spot but the water hasn’t penetrated to the roots of my rose bushes. You have written that you accept black spot as a non-lethal annoyance, but I really find it so unsightly as to be tempted to use a fungicide. You recommend deep watering too.  I have used soaker hoses, which seem mostly to benefit the grass and weeds choking the bushes. And I expect my water bill to be enormous. Should I accept that too as inevitable?

Irritated Irrigator on Ingraham Street


Dear Irritated Irrigator,

First, there are organic solutions to black spot if you really can’t tolerate it. Longwood Gardens has been using a solution of baking soda and ultrafine horticultural  oil as a preventative measure since 1993, and it keeps down powdery mildew as well. (The ratio is 1 tbsp. baking soda to 2 1/2 tbsp. oil.) Next year, start spraying your bushes with this solution every other week from April to late July, then weekly during August and September.

Now about deep watering and your water bill. Several years ago my rose-gardening mentor Citizen Cane cut lengths of PVC pipe and pounded one or two of them into the ground next to each of my roses bushes. They are about 2 inches in diameter and an average of 2 feet long.

Weekly in the summer, if we don’t get soaking rain, I fill the pipes with water that goes straight to the roots of the roses without waste of any kind. Rain water is far better for roses than chlorinated city water, so I try to collect and use as much of it as possible.

The telltale pattern on this rose leaf gives black-spot disease its name. Miss Floribunda has ideas on how to nip it in the bud.

Here’s where you are in luck. You may have noticed in your yearly county tax bill a notification about rebates for a number of ecologically beneficial measures: rain gardens, green roofs, and the like. You also get a rebate for rain barrels, which cost as little as $15 if you use throwaway syrup barrels from a local soft-drink bottling plant or as much as $200 if you want something especially elegant.

To qualify for a rebate, you must have at least two barrels that hold 55 gallons each. I don’t know how many rose bushes you have, but you probably need at least two rain barrels anyway.  For specifics go to Prince George’s County’s stormwater management webpage and click the rain check tab.

Right now I am waiting to see if Citizen Cane is successful with a new experiment of his. He is mixing quantities of those gel water beads used in hydroponics into the soil around his roses to see if they will help with water retention. I’ll get back to you on that when I find out if he has success and after I try it myself.

However, I do offer one last tip that is tried and true: When the weather is fiendishly hot, don’t permit your hybrid tea roses to bloom. I de-bud mine during the dog days so that more energy will go into healthy foliage and a stronger root system. Shrub roses and  annuals like zinnias and petunias can provide color for a while and scented herbs, especially rose geraniums, can delightfully perfume your garden.

The next meeting of the Hyattsville Horticultural Society is Saturday, October 19, from 10 a.m. to noon. There will be a plant exchange at the home of Joe Buriel and Dave Roeder, at 3909 Longfellow Street.  Bring plants that have overspread their boundaries and swap them for other plants new to your garden.



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