Roses, while popular among gardeners all over the world, are known to be host to a variety of issues. Many of these problems can cause a weathered appearance in the plant, including yellow leaves, under-developed flowers and improper growth within the plant. Successfully acknowledging and treating these issues can mean the difference between a remarkable garden and an unattractive wasteland.
Both plants and animals need a constant supply of nutrients for continued health and proper growth. Deficiencies with these nutrients can create a variety of symptoms in roses. Both magnesium and iron are needed for proper chlorophyll production, resulting in dark green foliage, and are necessary for the photosynthetic process to occur. Nitrogen stimulates the growth of the rose plants and sulfur is a building block for multiple proteins and amino acids that promote strong root development. Without these nutrients a plant is unable to produce fully developed organs and will result in yellowing leaves. Routine fertilization with rose-specific fertilizer is a quick solution for any gardener experiencing nutrient deficiency in their roses. Follow all of the manufacturers instructions when applying fertilizer to your rose bush.
Excessive irrigation, lack of drainage, and constant rainfall are common reasons for yellow leaves to appear on rose bushes. Too much water with displace the air in the soil and overtax roots which become too stressed to handle excessive heat in following summers. According to "200 Tips for Growing Beautiful Roses" by Barbara Ashmun, roses should always be watered from the bottom since droplets on the leaves can focus sunlight and damage them. Rose bushes should only receive 1 to 2 inches of water per week.
Gardeners must be wary of applying fertilizers with high amounts of potassium nitrate and ammonium nitrate. These ingredients are responsible for high accumulation of salts within the soil. As salt levels rise in the soil, it begins to absorb large amounts of water, leaving the roses in drought-like conditions which will result in symptoms ranging from yellowing leaves to death for the plant. Chlorides found in rain water can also contain dissolved salts and cause salt stress for the rose.
Spraying roses with insecticides can have the unexpected side effect of causing suffocation within the plant. The chemicals, when sprayed on the surface of the rose, can clog the pores of the plant blocking moisture and gases from entering or exiting the plant. The result is the inability for the rose to produce chlorophyll necessary for food production. As chlorophyll stops being produced, the leaves begin to yellow. It should be noted by gardeners that herbicides are highly volatile chemicals and are able to spread from their intended location up to a few hundred feet. These drifting chemicals are just as likely to suffocate nearby rose bushes as those sprayed directly on the surface of the leaves.
A variety of pests are attracted to roses and will suck nutrients directly from the plant, leaving the leaves and stems withered. Whiteflies, aphids, scales and mealybug are dangerous to rose bushes. They are able to pierce leaf and stem tissue and attract other pests into the area as they feed, including the fungal disease Black Spot. Gardeners should be very careful about infestation. Insecticides are known to effectively remove both current infestations and prevent future problems. Be sure to read and follow all manufacturer's instructions accurately when applying these chemicals to your plant.