Answer: If it has bloomed well in past years, then the feeding of thrips or aphids on the flower buds may have killed them. Take a close look to see if there are clusters of aphids on new growth. Thrips are difficult to see without a magnifying glass.
If blooms has declined over the last several years, the plant probably needs rejuvenation, or has been shaded by the growth of surrounding trees. Oleanders bloom best in full sun. To rejuvenate an old shrub, cut it back completely to the ground. But before you do this, fertilize heavily with cottonseed meal and manure a year or two before to help the plant withstand the shock. Do heavy pruning of this type in late winter or very early spring, before growth begins. Best of luck!
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