Roses not bloomibng - Knowledgebase Question

Kingman, Ar
Question by richjanh
June 30, 2010
These three rose bushes have been around for many rears. We give them food and water. It's like two bloomed once then no more. Some leaves have turned yellow. ?? What can we do ??


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Answer from NGA
June 30, 2010

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I apologize for the delay in responding. We were flooded with questions and are working to catch up!

Roses need two things for blooms: sun and nutrients. Are your plants receiving at least 6-8 hours of sun daily? Nitrogen, phosphorous and potassium are the 3 major nutrients for all plants. (They correspond to the 3 numbers on fertilizer packages, such as 15-30-15.) Nitrogen promotes growth of green leaves. Phosphorous is essential for blooms. The second and third numbers on the package should be higher than the first. The thing to avoid is feeding them with high-nitrogen fertilizer, such as 21-0-0, that will encourage foliage growth at the expense of flowers. Fertilize with a slow-release fertilizer every 6 weeks starting after pruning in late winter, continuing until June. Some rosarians continue feeding at half-strength through the summer, others stop, thinking it is too stressful for the roses. Begin feeding again in September, with the last application in mid-October. Don't feed during the cold winter months, as fertilizer promotes tender new growth which is susceptible to frost damage. Tt's a good idea to layer several inches of organic mulch around the base to maintain soil moisture and cool soil temperatures.

Most hybrid roses are grafted onto a hardier rootstock. If the grafted variety succumbs to cold or disease, the rootstock often sends up shoots. You may be able to see if this is the case, depending on if the graft union was buried when the roses were planted. The graft union is a slightly bulging area at the base of the plant. It should be planted above ground, but sometimes it is planted below ground. If the shoots are growing from below the graft unions, the rootstocks have taken over, which could explain the lack of blooms.

Finally, water should soak through the entire root zone, about 2 feet deep, with each irrigation. Shallow watering may contribute to the build-up of salts in the root zone, which could be the cause of yellowing. Yellow leaves can be caused by many other things including lack of nitrogen, insufficient light, water-logged soil (plant roots need oxygen to thrive), dry soil, or iron deficiency. If the older bottom leaves are yellow, but new growth is green, it's usually a lack of nitrogen. If new leaves are yellow, with green veins, it's usually a lack of iron. (Lack of nitrogen is a more common problem than lack of iron.) Soil should be kept moderately moist (but not wet). Try to isolate each of these possibilities one at a time to determine the problem. Good luck!

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