Get Your Roses Through Summer!
by Satish Prabhu, Master Rosarian, Carolina District Rose Society
Of many reasons why our region has a reputation for making it very hard to grow roses, challenges of summer rank first! High humidity, and high average daily temperature and lack of rains all take their toll on our roses. Let us briefly review various diseases of roses and summer challenges and ways to mitigate the same in our gardens.
First and foremost, a well prepared soil with good drainage and ample amounts of organic matter would be helpful in draining excess water while holding adequate amounts of water in the soil for the plants to take up between watering would be most helpful. What if the soil was not adequately prepared before planting roses? There are a few things we can do to mitigate this problem. A layer of compost spread on the rose bed, about one inch thick and covered by pine straw or hardwood mulch goes a long way in building up soil. Left undisturbed, earth worms will assist in taking organic matter deeper into soil. As soil organisms break down compost further, gradually, topsoil is formed and added to our beds. It was generally accepted that it takes nature something like a hundred years to build a couple of inches of top soil. However, it is now thought that with human help in the form of initially providing a large amount of organic materials, such as compost, incorporating the same into the upper twelve inches of the indigenous soil only once, initially and then mulching and leaving the soil undisturbed and then allowing the earthworms and all the beneficial soil organisms do their thing, results in several inches of good soil in just a few years.
Mulching helps keep the soil temperature moderated as compared to un-mulched beds and by protecting the soil from exposure to direct sunlight, it slows down drying of the soil and helps conserve moisture. The mulch also helps control germination of weed seeds. Finally, mulch adds to beautification of rose garden. Just make sure about a square foot of space immediately surrounding the base of the rose bush is clear of mulch; because allowing any organic mulch in immediate contact with the base of roses is said to possibly cause various diseases of rose canes. (Thick mulch around tree bases is said to assist damage of bark by rodents!)
It is important to keep roses watered adequately throughout summer. Allowing the soil to dry completely between watering can produce severe strain to which plants can succumb! One can see wilted plants recover within hours of replenishing moisture in the soil. However, if they reach a stage termed ‘terminal wilting’, the plants will not recover. How often to water plants is a matter of extensive discussion and debate. Many English gardening books call for “deep watering” of roses once a week. Another oft-repeated formula is one inch of water per week. More specifically, if you do not get an inch of rain in any week, irrigate your roses heavily. It is interesting to note that when Mr. Tom Carruth took over the charge of Huntington Gardens, he noted that roses were watered too often and over-watered. As expensive as water was in California, they spent enormous amounts of money on watering the rose garden. He felt that they were watered much more often than really indicated. When roses are watered daily and superficially, one can see large amounts of superficial fibrous, feeder roots develop mostly in an area immediately below the mulch and frequently in undisturbed organic mulch. When they are not watered daily, the superficial layers of soil dry quickly and those roses with a lot of superficial roots and not enough deep roots will wilt. Hence they should be watered daily during the hot summers of Carolinas. However, when the soil is prepared properly to a depth of 18-inches and roses are watered deeply once a week, Roots run deep in search of water and those roses will stay healthy in summer. Tom Carruth ordered roses watered deeply and only once a week and he tolerated slight wilting of plants between watering intervals, beginning in the spring. He was soon able to “re-train” his roses to develop deep roots and seek water deeper in the soil! Most of us common gardeners, however will find ourselves watering our roses every day or at least every other day when it does not rain and the outside daily temperatures are very high in the summer months. A common- sense approach would be to gently move aside the mulch and scratch the surface of the soil and if the top inch appears to be dry, it is time to water! What if one has a drip system or other watering system installed in one’s garden? Then it becomes important to closely monitor the system to make sure it works as intended; all emitters and heads are open and functioning properly. Clogged up emitters and heads give rise to dry areas in rose beds and as a consequence of which, plants can suffer. Watering deeply and only once every few days applies only to established bushes. Newly planted bushes should be watered every day to help them develop roots and get established.
Over-fertilizing roses in summer could result in un-intended harm to rose plants. Applying chemical fertilizers to soil causes the electrical conductivity to rise. Ideally, one would keep electrical conductivity well below 1.0. When the salt concentration in soil exceeds salt concentration in the plant tissue, water is drawn out of plants into the hypertonic soil (reverse osmosis). This can happen in three ways. The first one is a result of simply applying a soluble fertilizer such as Miracle Gro or Peter’s special or equivalent in excess of what is recommended. (Please note that both are excellent and safe fertilizers when used appropriately! The problem is caused by excess application!) Second way is applying the correct, recommended dose, such as three cups to 400 square ft. of bed space or two tablespoons per established rose bush etc., but dissolved in less water than recommended amounts of water or not applying adequate amount of water immediately after sprinkling the fertilizer on the soil. The third way damage can occur is when correct amount of fertilizer is applied in recommended amount of water, but the soil is allowed to dry in subsequent days, so that, once again, the salt concentration is the soil rises! Because of this concern, many rosarians recommend applying only half the recommended amounts of fertilizers in the summer and do it twice as often. While roses are growing faster and producing more blooms in summer, more nutrients are needed and not less! Applying organic fertilizers such as compost and/or fish emulsion helps keep soil fertility up during the summer months.
Black spot is very common in South Carolina. It gets worse in the summer as the plants are already stressed and the rosarians take a break in the summer months and leave their plants alone, to fend for themselves. This complicates the matter. There are many rosarians who try to fight blackspot without spraying chemicals. It is a very laudable effort! Start with planting blackspot resistant varieties. However, understand and realize what that term precisely means! Mostly, a black spot resistant variety means that when the disease appears in your garden and many plants are infected, the resistant varieties are the last or later ones to show the symptoms! It does not mean they will not get blackspot. Further, it has been shown that when a rose appears to be blackspot resistant in one trial garden in a particular area of the world, the same may not hold true in your garden as strains of blackspot prevalent in your area might be very different and hence, the same variety might show blackspot readily in your garden. The next step is to promote conditions that help plants to withstand the attack. Give each plant adequate space to grow, avoid over-crowding and keep the centers of the plant thinned out and free from blind ends. Avoid watering plants in the evening instead of morning and avoid making the foliage wet and so on and so forth. Finally, people have enjoyed a measure of success using the so-called organic remedies, of which many are marketed. If some of these measures work satisfactorily for you, well and good! If not, then you have to decide whether or not you are going to follow a maintenance spray program. For small gardens, Bayer’s systemic products are available, which can be sprinkled on the soil in precisely recommended amounts at prescribed intervals and watered in. These systemically effective chemicals are taken up by the roots and held in plant tissue for a certain length of time during which the plants are protected from the diseases and pests specified on the label. Reportedly, they are effective in keeping the plants healthy and protected from fungal diseases, insects and spider mites! For larger gardens, there are many preventive spray regimens. Please refer to http://rosemania.com
for recommendations. Also, you can find similar information on various websites of local rose societies and the district web sites. The best source of information is the consulting rosarian manual, which comes as printed pages, with or without the binder for 15 dollars, from the American Rose Society. This manual gives us access to the collective wisdom of all C.R.s in the country, compiled for general use. The same can be accessed free of charge if you are a member of the American Rose Society in the members only section of the ARS website.
My own program is to spray with Banner Maxx with Mancozeb or Dithane, every seven to ten days. I do alternate Banner Maxx with Compass every other time. Steve Jones recently wrote that including one of the phosphonate compound fungicides, when included in the rotation on at least once a month basis, strengthens the black spot protection and helps stave off downy mildew. When blackspot does appear, a recommended course of attack is to apply Dithane every three days for a total of three times, remove all affected foliage and dispose them off in plastic bags and then resume your preventive spray program.
Spider mites can appear and multiply very rapidly in the summer. They are said to reproduce a new generation every three to four days when the weather is very hot. The first symptom you notice might be a parched appearance of your foliage and formation of some webs may also be seen. Affected foliage drops off causing extensive defoliation in the rose garden, often killing the rose bush. The simplest remedy is to wash off the under surfaces of foliage every other day with a device called a water wand. The water wand may now be not available for sale, but the Foggit Nozzle, high output, attached to an extension wand on a hose pipe will do just as well. Many rosarians report good success using just this technique. There are no known effective organic miticides, but there might be some that are being marketed for the purpose. Common insecticides are ineffective in killing spider mites and using them may make the mites problem worse by killing off predator insects of spider mites. A rotation of Avid, and Floramite, and spraying these miticides as soon as one sees first evidence of presence of mites can help control them. Forbid is another excellent miticide to use in rotation.
The Japanese Beetles have started appearing in South Carolina gardens with regularity. B.T (bacillus thurigensis) treatment is reportedly effective, but to be somewhat successful, all gardens in the neighborhood will have to apply B.T. in their entire yards each spring. However, Japanese beetles, while eating up all flowers and a large amount of leaves, will not cause any permanent damage to the plants. If fertilized and watered properly, these bushes, ravaged by Japanese beetles, will bounce back to produce roses satisfactorily in the ensuing cooler months of fall.
One must consider deadheading roses as a very important chore throughout the summer months. It is natural for the blooms to become smaller and contain fewer petals, get burnt on exposure to very hot sun and generally look pitiful. One would be tempted not to bother with regular dead heading. But leaving the spent blooms on the plant, particularly those varieties which tend to hang on to petals on the spent blooms instead of cleanly dropping them off can invite disaster. This allows botrytis to set in on those spent blooms when they are exposed to rain or otherwise get wet. These petals which carry botrytis will eventually fall and botrytis will take residence in the rose soil in the form of spores, waiting for an opportunity to jump on your beautiful blooms in fall. Even a minor affliction with botrytis will render your blooms totally not fit for exhibition! Therefore, it is important to remove all spent blooms in a timely manner throughout the growing season!
While deadheading, pay attention to the bush and note its size and rootstock and varietal characteristics. Thus, on very small and freshly planted bushes, it is only necessary to remove just the spent blooms. But on established bushes, after the first flush of blooming is finished, one should take the opportunity to generally clean up the bush by removing any spindly growth and blind shoots in the middle of the bush, so on and so forth so the bush looks clean and airy. When the bush looks very dense and boxwood-like, it is advisable to remove a few select stems from the center of the bush to thin them out. Further, if you are looking at an established bush on a fortuniana root stock, which tends to grow very tall in the fall, you would do well to cut back fairly long stems with each bloom or each dead heading. This will give you an opportunity to work on bushes which are only about six feet tall in the Middle of August, which you can cut back to about four feet as part of your fall pruning. This will give you an opportunity have fall roses blooming at approximately 6 ft. in height, so that one could handle the chores of stabilizing the bush and protecting the blooms for fall shows, so on and so forth! More on that to come in the mid-summer issue.
One should be aware that when the temperature climbs up to high 90s and 100s, growth will slow down and almost completely cease; this is very common and normal and nothing to worry about.
Lastly, summer is the time to evaluate your garden and make appropriate plans for next year. It could be making new beds, moving existing roses to a new and better suited location in your yard, expanding or reducing the size of your rose garden, and perhaps replacing some of your roses with better cultivars, for choice of color, form or fragrance, so on and so forth!
So stay cool indoors, but do not neglect your roses in summer! A little bit of attention paid to them now will pay huge dividends in September and October in the form of great roses!
Photos of Prahbu garden, all by Satish Prahbu