Roses can be an idyllic addition to any garden or landscape, but they can also be a challenge to grow for numerous reasons. Roses that grow in the shade are twice as susceptible to problems as roses that grow in full sun (at least for most of the day), which is what they need. Roses are usually disease-free, but do encounter occasional problems.
Bottom Leaves Yellowing and Dropping Off
Bad drainage is the most common problem with growing roses, and the rose will start to show signs of being stressed out. The first sign of bad drainage is when you notice the bottom leaves of the rose (usually the oldest) begin turning bright yellow, then drop off, eventually leaving the stems bare. The veins and the central areas of the leaves turn yellow first. The rose blooms appear smaller and weak. With bad drainage, the roots could be waterlogged and not have enough air circulation. This can make the rose plant more susceptible to fungi and bacteria infections.
Green Slime or Moss
If your roses are getting too much water, you may notice moss or slime growing around the base of the rose bush. This is not fatal if you catch it and fix it right away. Unfortunately, this can be caused from the type of soil you have, especially if it is clay soil. First, stop watering the roses so much or improve the drainage of your soil, so the roses don't die.
General Plant Decline
Roses will most likely all experience a general decline at some point. If you notice your rose bushes losing leaves or branches, it is generally known as the condition called canker, which means the roses are suffering from fungal or bacterial disease. The disease is typified by rose canes slowly turning black at the bottom, then slowly at the top, until the rose blossoms are dead. This can be identified as bad drainage or root rot, but there could be other reasons depending on your environment. Consult your local nursery to see what may be harming roses in your area.