I’m often asked rose questions. Thought I share a few.
1) Asked last August. “Some of my rose leaves are turning yellow”
The problem is usually too much or two little water. As a general rule, if a yellow leaf pulls off easily that could be too much water. If the leaf is harder to pull off and possibly some leaves have brown dead edges and tips, probably too little water. Suggest continual checking the soil moisture content with a probe. If late summer-fall and mostly lower leaves starting to yellow, probably natural aging. (When I checked these roses, were way over watered.)
2) Late summer call. “My roses look healthy, lots of growth but little bloom.”
I asked if fertilizing. Said, “Fertilizing monthly with Miracle Gro.” Well, that’s likely the problem, over fertilizing and using a high nitrogen content chemical fertilizer.
I recommend a chemical fertilizer, such as Miracle Gro, that has a higher amount of nitrogen (“N”) than the other two main nutrients, phosphate (“P”) and potassium (“K”) for the first feeding as the roses start to leaf out from their winter pruning. The advantage of a chemical fertilizer is that the nutrients are more broken down so the roses can faster absorb the nutrients than using an organic fertilizer.
For a second feeding, around the 4th of July, best to use a balanced organic fertilizer. The “N-P-K” on the label should have about the same percentage of each nutrient.
A possible final organic fertilizing may be done late summer-early fall of mostly potassium and no nitrogen. Unless I see some rose structure weakness, I generally do not do a late season fertilizing since there is likely adequate potassium in the soil from the earlier feedings.
Regarding trace minerals, they are in most commercial fertilizers. Also, our Bay Area roses generally get adequate trace minerals from the drinking water.
3) Asked this January, “I have lots of rust on my roses and spider mites at the bottom. What should I do?”
Recommend removing all diseased leaves as part of the winter pruning. When finished winter pruning, rake out and remove all debris in the beds followed by spraying the pruned plants and surrounding ground with a horticultural oil. Most nurseries sell the oil in a bottle that attaches to the hose…a bit more expensive but very convenient.
For spider mites, once roses leaf out, continually remove diseased leaves and any weak “junk” growth at the bottom of the plant, at least 6-8? for “normal” sized plants, and continue to do so throughout the year. This should dramatically reduce or eliminate the spider mite problem.
For rust and black spot, also continually removing all diseased leaves from the plant and ground. I’ve noted that owners prefer not to remove diseased leaves as the roses are about to produce their first spring bloom, “It makes the plant look so naked.” I agree, but the replacement leaves will soon grow back, often with little or no disease.
Happy gardening, Royal