Answer: There are a number of possible reasons:
If the new leaves and shoots on your roses appear as light yellow green to white with darker green veins showing, it could be chlorosis or iron deficiency. This is the most common and apparent deficiency to occur in roses. Photosynthesis needs iron in order to work. If there is no iron there is no chlorophyll, hence the rose leaves cannot turn green. This is most commonly caused by clay soils. Certain kinds of clay (clays are a group of several different minerals) 'eat' iron as they go about the process of chemical weathering.
If this describes your rose, you'll need to add chelated iron to the soil on a regular basis. Just a handful around the base of the plant out to about 1 foot in radius is enough to start fix the problem usually. There are some iron additives that include nitrogen fertilizers with them, so that you can kill two birds with one stone.
Another common cause is Mangnesium deficiency. In this case, the leaves are pale and yellow in the center with dead areas close to the middle of the leaf. Oldest leaves are the first affected. Leaves fall off the plant early. To treat, use a fertilizer containing Magnesium.
Nitrogen deficiency will cause the young leaves to appear small and pale green. Veins are a lighter yellow color. Rusty red spots sometimes develop in the center of the leaves. Stems appear small and short. The overall rose becomes stunted or even defoliated. This is caused by the rose using up all of the available nitrogen in the soil, or by the breakdown of too much wood or bark mulch or fall leaves. Balancing your mulch with grass clippings can help you with this situation.
Best wishes with your rose!
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