ROSES -- BLACK SPOT -- POWDERY MILDEW -- MILK 2: 22 April 2004
GWE e-mails from Tennessee, U S A: I am looking forward to trying your milk recipe to prevent blight on my tomatoes. Do you also have an organic method for dealing with black spot and powdery mildew on roses?
R J Harris replies: "These are separate and different problems and are best dealt with separately.
"Powdery mildew first.
"Use the milk solution, as for tomatoes. Exactly the same procedure."
To find this procedure, link to milk 1. Use the back button to return.
"For the black spot," continues Mr Harris, "see this as a good sign as well as a nuisance that must be corrected. It is the price that the rose lover pays for living where the air is unpolluted by the burning of fossil fuels."
No wonder, the head gardener commented, that the city dwellers of the industrial societies of the eighteen and nineteen hundreds were able to grow such marvellous blossoms. Indeed, in the U K, that was the position right up to and beyond World War II. Even now, he noted -- in 2004 -- there were towns of the United Kingdom where the local authorities refused to introduce clean air zones, and permitted the burning of raw coal in domestic grates.
"In short, dirty air kills off the spores of the black spot," he summed up, "and leaves the roses with clean faces."
Soot was one organic cure, if it could be obtained -- soot created by the burning of coal and taken from the domestic chimney, not from the burning by any means of gasoline or oil or wood.
"Wait for the affected bush to become fully dormant," he prescribed. "In the U K that is in November, December and January. Choose a windfree day when the weather is truly miserable, a damp and wet day, when it is no time for sensible human beings to be in the garden.
"Remove every bit of the mulch and debris that is on the earth around the plant's base. Do so with the least disturbance to the lifted mulch. In fact, good practice is to take it up in small, undisturbed quantities which are immediately and carefully placed into a plastic bag, with the top of the bag being kept closed until more has to be added. At the end of the job, tie up the bag or bags tightly and take them off site for disposal in a safe kind of way. You can be sure that what you cart away in this very controlled manner contains black spot spores just waiting to rise up and settle on the new growth as the season improves and the plants revive from their dormancy.
"With the old, infected mulch removed, apply the soot to the plant -- a handful or so scattered over what at this time of the year are pruned branches. Then spread it on the ground -- a large handful to the square yard or square metre of surface. The damp conditions will encourage it to stick to wherever it is put, which is what you want."
The operation must be repeated six weeks later.
"If soot is not to be had," continued the head gardener, "and judging by her words, this lady gardens where little coal is burned domestically, then, in exactly the same way, with exactly the same rate of application, use charcoal that has been ground up into charcoal dust. You can get it by the bag from the merchants who sell charcoal for the barbeque and other cooking devices."
Crushing charcoal at home was not to be attempted, R J Harris warned. Only the finest of dust did the job, and achieving that grade with domestic aids was well nigh impossible. Attempting to do so was also the messiest of jobs. "With this treatment completed, you can begin the new growing season by appplying the start-of-season feed followed by the putting on of fresh mulch to conserve moisture and condition the ground.
"A point to bear in mind," he added, "is that roses are very, very vigorous feeders. Correctly fed, they are best equipped to fight off these two pests. Starved, they are sitting targets."
Mr Harris recommended that the individual plant be given a ration of standard fish, blood and bone fertiliser every six weeks in the growing season, receiving it at the rate of three ounces or 84 grammes to the square yard or square metre.
Those who were putting roses into their gardens for the first time should note that black-spot-immune plants were now available. If the neighbours' roses showed that the disease was common, these specially-bred varieties were the ones to buy. Any reputable horticultural centre would supply them.
"And," Mr Harris noted, "in fairness, be it said that there are any number of commercial products that can be bought that deal with powdery mildew and black spot the laboratory way. They are not organic, of course, and they are not cheap, but they are widely available and they come with detailed usage instructions -- and those two things, for the many people who do not have the time or the opportunity to become real gardeners, is the supreme advantage."
The head gardener advised, finally, "Whether using soot or charcoal dust, wear a mask over the mouth and nose and goggles over the eyes.
"No matter how carefully either of these powders is handled, and no matter how wet and miserable the weather conditions, they tend to fly around. Incidentally, that is a good reason to wear the oldest clothes at the same time, or the most washable of clothes. The applied material may be organic, but, truly, it is filthy stuff."
p For moon gardeners, Mr Harris's words on striking back against powdery mildew and black spot result in some interesting thinking. Of the lunar quarters -- first, second, third or fourth -- the soot or charcoal dust is best applied when an adequately damp day coincides with the start of the second quarter. At this time, Earth's water table is on the rise, drawn up by the moon's increasing gravitational pull. It has roughly a week in front of it of further rising. For that reason, it is a period of increasing upward pressure upon the garden's top soil. The applied soot or charcoal dust is discouraged, thus, from penetrating the earth's surface, and has become a thin crust upon the earth's surface by the time the water table begins to fall and its upward pressure is relaxed. As a crust, it cannot be absorbed. Of course, if the ideal soggy weather does not coincide with the ideal moon moment, moon considerations must be placed to one side and preference given to weather conditions. Luckily, soot and charcoal dust are highly vulnerable to damp in the atmosphere, and quickly absorb it. The reverse of this is true with regard to the use of fertiliser. The start of the fourth quarter is the ideal time to scatter this powder upon the ground, for, then, the water table is falling and its relaxing pressure renders the top soil especially receptive to whatever is applied to it.
p Discussing GWE's questions in general terms, and referring especially to moon matters, R J Harris talked about his way with the pruning of the bush rose. "Quite simply," he said, "I prune off one third of the individual plant's height in November -- or when the end of the growing season brings the commencement of dormancy -- and then I repeat that in March -- or just before the growing season begins." He added: "Of course, I apply the general rule regarding the pruning of any type of plant, and I cut at the start of the fourth quarter. This is when the pressure from the water table is falling, because the water table itself is falling. That means reduced pressure upon the plant's root system and, therefore, reduced loss of sap as the cut is made. That helps the plant to recover from the surgery."
p Mr Harris commented on the problem of the established rose bed in which one or two plants have to be removed, leaving gaps. "All rose growers know," he said, "that the last thing you do is insert new bushes into ground that has already supported roses -- probably, over many years. But leaving the ugly gaps is not an option, and neither is renewing the whole bed with a depth of imported, fresh soil and fresh plants. So, in go the one or two new roses where the previous ones came out and during the season of dormancy, and everything is done to help them to make the best of what is, in fact, rose-exhausted soil. Anyway, that is what would be the standard practice." The head gardener continued: "My advice is 1) give the whole bed the first stage of the black-spot treatment. In other words, remove the old, contaminated mulch -- all of it -- and dispose of it off site, 2) take out the one or two plants that have got to go. Do this so that the affected soil is disturbed as little as possible and certainly not scattered all around. Remember, no matter how thoroughly and carefully the old mulch is lifted, black-spot spores remain in the surface soil. They must be left there, as undisturbed as possible, 3) insert the new plants -- again, creating as little soil disturbance as possible, 4) then -- importantly -- do not water in the new plants using a high-pressure hose. Use a watering can, and do so gently. Water applied with vigour splashes up onto the plants, taking the spores with it and putting them exactly where they are not wanted, 5) with the new plants in, give the whole bed the soot or crushed charcoal treatment. And remember that this, now, is a rose bed that must have, as a continung thing, the full, caring treatment of regular, proper feeding and regular, proper maintenance. It has become a vulnerable bed, and will be even more at risk than rose beds normally are."
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