Healthy Roses Michael Marriott Many gardeners are so obsessed about their roses succumbing to pests and diseases that they often forget to notice how beautiful they are. Indeed, this susceptibility to infection probably explains why some gardeners do not grow roses. Those who do often choose modern varieties that may resist disease; but these varieties often lack the beauty and charm that we normally associate with roses. In this article I am discussing ways of overcoming pests and diseases; these methods can also be effective against most other problems that may affect roses. There are four basics to remember if you want to grow healthy roses: 1) grow resistant varieties; 2) space planting to encourage health; 3) encourage optimum growth; 4) take action against pests/diseases. Growing resistant varieties     Roses that flower only once are generally much more resistant to disease, partly because of their genetic character, but also because they do only flower once. By contrast, repeat flowering roses use up much of their energy in the production of flowers and this can make thern more prone to disease. Therefore the species such as Gallicas, Damasks, Albas, and Centifolias, the once flowering Modern Shrubs, and to a certain extent the Mosses often have excellent disease resistance. Even if they do succumb they drop their diseased leaves and continue growing and seem otherwise unaffected. My 'Fantin Latour', is never sprayed, gets blackspot badly every year yet still flowers freely. After all, many of these old varieties have already survived for centuries without any sprays. Therefore choose your type of roses carefully; if they do get disease, and are once flowering, try to avert your eye! The Rugosas are very much the exception that proves the rule: although they repeat flower most do not suffer from disease or pests at all. The repeat flowering shrub roses vary greatly in their ability to resist disease. As many are excellent and beautiful it is worth seeking advice when choosing.     The introduction of the repeat flowering gene from China immediately spelt trouble for roses from a disease viewpoint and in particular the Bourbons, Hybrid Perpetuals and early Hybrid Teas, none of which are disease resistant. However, now there are many excellent Hybrid Teas and Floribundas that have good resistance. Indeed, disease resistance is one of the main concerns of breeders, sometimes unfortunately to the detriment of other characteristics.     The degree of resistance to diseases shown by different varieties is well documented. However, the resistance to pests is less clear. The red spider mite seems to favour some varieties such as 'Ballerina'. I've not heard of any particular variety that is resistant to aphids and so I would be interested to hear from anybody who has. The planting scheme     There is nothing I hate more in a garden than a bed sparsely planted up with roses with 'acres' of bare trampled soil in between. However, a border planted abundantly yet solely with roses can be a wonderful sight, but it is also a wonderful way to encourage pests and diseases. When planting roses bear in mind their eventual size so that they will not over-crowd each other; the more closely they are planted together, the easier it is for pests and diseases to rnigrate from rose to rose.     An alternative is to separate the roses by interspersing with herbaceous plants or shrubs. The spores and/or insects cannot spread so easily from one rose to the next and levels will be kept down. At the RHS garden at Rosemoor in Devon they have created a wonderful double herbaceous border with old and shrub roses mixed in. Wollerton Old Hall near Market Drayton in Shropshire is another good example. However the herbaceous plants should not be allowed to become too invasive as they will starve the roses of nutrients and water. Herbaceous flowers and roses do complement each other wonderfully and with many herbaceous plants in flower, the once flowering roses will not be seen as a disadvantage. Optimum growth     Gardeners are an acquisitive lot and often try to grow the most fastidious plants and certainly the most temperamental roses. Many varieties that are extremely beautiful need that little extra bit of care, although I often think they appear more beautiful because they need more attention.     Roses have a natural resistance to disease and this can be optimised, if the plant is growing strongly. Gertrude Jekyll and Edward Morley wrote about it in Roses For English Gardens. More recently Dr Tommy Caimes from the USA has suggested that when plants are not growing well they produce fewer sugars and are then less able to sustain their internal resistance mechanisms.     So how do we grow roses well? Their planting position is crucial. They like plenty of sun and although a few will put up with shady spots, most dislike being shaded or having too much competition at the roots.     Above all roses love humus - and plenty of it - applied before planting. After planting it is too late. Well rotted manure is the best but it is not easy to come by. However Garden Centres now sell it in plastic bags, although it often contains a fair proportion of bark. Garden compost is also excellent.     Many gardeners who grow their roses so well do swear by the use of copious quantities of manure. Here at Austin's Nursery the soil is very sandy and so we ensure that we have a plentiful supply of manure from local farmers and stables. Manure and compost will also help neutralize the pH of a soil that is too acid or too alkaline. Humus is essential in conserving moisture, as a source of nutrients, and as a medium for the beneficial fungi and bacteria. Similarly, on heavy clay soils, manure is extremely valuable as it not only helps break up the clay, but it conserves moisture and stops it cracking, so making it more manageable. Bone meal should be mixed in with the soil when planting; it is a good source of nutrients that will be slowly released into the soil.     Annual doses of humus should be added as a mulch in the spring after the fertilizer. This has several benefits: it maintains existing humus levels; retains the moisture in the soil; encourages worm activity so keeping the soil structure open; lowers the temperature of the soil which the roots enjoy; and it buries the over-wintering spores so that the soil will remain microbiologically active. Humus also helps prevent soil compaction often caused by too much walking or standing. Within reason, it really is a matter of 'the more the merrier', and, as long as your mulch is initially free of weed seeds, humus will discourage weeds from growing. In the USA during those dry summers they have applied very thick layers as a mulch and they do not suffer from replant disease; I have a strong feeling they are related.     Ideally the mulch should be well rotted manure, but spent mushroom compost or garden compost or even wood chips or bark are suitable. However do note that whereas the first three will add nutrients to the ground from the time of application, the latter two will, initially at least, take nitrogen out of the ground. Also bark tends to make the soil more acidic, so it is not recommended on already acid soils. Conversely spent mushroom compost will make soils more alkaline and so is not satisfactory on chalk.     Most roses are hungry feeders especially the repeat flowering varieties and so they benefit greatly from fertilizer. Do make sure it is a well balanced fertilizer, and that it contains not only nitrogen, phosphorus and potassium, but also micronutrients. Recent research has shown that micronutrients are particularly important in encouraging disease resistance. Manure of course, is a good source but to be on the safe side choose a fertilizer that contains micronutrients. Manures, composts etc. are often low in nitrogen, so an additional source is important.     We use Vitax Q4 at the nursery with excellent results. At the Gardens of The Royal National Rose Society at St Albans 'Top Rose' and Phostrogen is used. If only one or two applications are made then ensure that the nitrogen in the fertilizer is fairly long lasting. If it is solely inorganic then more frequent applications should be made. Vitax Q4 is semi organic and so some nitrogen is released immediately, the rest on a longer term basis. True slow release fertilizer can last the whole season, and so is excellent - although expensive!     If using Vitax Q4 or similar, once flowering roses need only one application each year. Apply early, say, in February or March when growth is beginning, The repeat flowering roses should be fed again in the summer in June when the flower buds are well formed and starting to open. Feeding is not recommended after this as it encourages soft growth which is prone to those diseases that prevail in the damper more humid autumn weather and of course the soft growth may not survive the winter. Products containing seaweed extract can be applied as a foliar feed as they seem to help disease resistance; we put it on our rose crop at the nursery. Pruning     Pruning is crucial to the well being and good flowering of most roses with the exception of species roses. However even they benefit from some thinning after a few years. Far too much has been written about pruning, making it over complicated and inaccessible to the beginner. The basic method is to prune out any dead, diseased stems for here spores can survive the winter ready to infect young leaves in the spring. In principle, the harder the pruning the better; however hard pruning will spoil the shape of old and shrub roses, and reduce the flowering of the non-repeats, so it is really a compromise. Killing spores during the winter is also important; some use Armillatox with apparently excellent results. Action against pests and diseases     I will discuss other ways of controlling pests and diseases in the spring issue next year. Michael Marriott was, for 15 years, the Nursery Manager at David Austin Roses. Now as their Technical Manager he is promoting roses, especially English Roses, throughout the world. He also gives technical advice, plans rose gardens and lectures widely. He is a passionate all round gardener and plantsman. This article appeared in the Autumn 1999 issue Return to the HRG magazine page Go forward to Healthy Roses, Part 2