Problems With Potted Roses in Desert

Find out why some potted roses do better than others in this warm area.

Q: About eight months ago, I purchased several tree roses in large pots. I have already lost one, and another is close behind. They were replanted in larger pots with good mulch soil. Two of the four remaining are doing well. One has new growth with wilted leaves. The other has lost most of its leaves, and the new growth gets brittle and dies. I've provided them with good irrigation, and they don't sit in water. Soil is kept moist but not wet. The leaves turn brown and crusty on the edges, then yellow and wilt. I was told that potted roses should be fertilized at every watering (I use a rose fertilizer), and it seemed to do well with the others, but not these two sick ones. I have also given them a good drenching to make sure the salt is washed out through the holes and used bone meal, but no noticeable improvement. What's wrong?

--Phoenix, Ariz.

A: It's unusual that you are having such a variety of symptoms when the conditions you are providing are the same. Are the roses all the same variety, or do you have different ones? If you have different varieties, perhaps some are better suited to the low desert than others. It sounds as if you are doing a good job of care. However, summers in the desert are extremely tough on roses, particularly those in pots.

Did you provide protection from afternoon sun? Soil temperatures in pots can reach 150 degrees F in summer. Container plants in these type of conditions benefit from afternoon shade during the summer. Stressed plants are more likely to show problems than non-stressed plants. Here are some potential reasons for the symptoms you describe:

  • Wilting leaves can be a sign of both dry soil (which you don't seem to have) and water-logged soil and/or root rot. Roots need oxygen as well as water, and if there is too much water in the soil, it fills up the spaces where oxygen would be. You seem aware of the importance of not having overly wet soil, but perhaps one pot is not draining well. Or the water is flowing down the sides and not soaking the root zone? Try digging down to ensure that the roots are in moist soil. A fungal disease called vascular wilt is another cause of wilting leaves.

  • When leaves turn brown and crusty on the edges, then die, it's often a sign of fertilizer or salt burn. Again, you seem aware of these problems and are leaching out the salts. However, most rosarians I know do not fertilize their roses during the summer because there is increased stress for the plants just surviving, let alone producing blooms. They fertilize every six weeks, starting in September, as the weather cools and go through November. Then they start again in mid-February through May, tapering off in June as the heat hits. Also with container plants, more regular fertilizing is often needed, but it's a good idea to use 1/4 to 1/2 the strength to reduce the chances of fertilizer burn.

  • For more information--there are several very active rose clubs in the Phoenix area. Visitors are always welcome at their meetings. Phoenix Home and Garden lists these clubs and their meeting times in their "Around Arizona" section at the back of the magazine.

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