Fertilizing is how we replenish the nutrients consumed by the plant. Plants should be fed if they are to remain healthy and produce good blooms.
There are two ways to feed the plant – with organic material or inorganic fertilizer. Organic materials such as manure, compost or meals (blood, fish, soy, kelp, etc.) feed the soil with additional bacteria, which, in turn, break down into inert mineral salts. These mineral salts are the compounds the plant will absorb as food. Inorganic fertilizers are generally faster acting than organic materials, since they require only dissolving in water to become available to the plant. However, organic materials are essential for a well-conditioned soil. Some Rosarians prefer to use organic fertilizers; most Rosarians use both.
All products labeled as fertilizer must have, by law, the percentages of nitrogen, phosphorus, and potassium listed in that order (N-P-K) on the container. Nitrogen produces vegetative growth; phosphorus promotes the root system and the bloom; potassium or potash stimulates the general health of the plant. If a granular commercial fertilizer is used, choose one with a balance between the three main chemical ingredients and, if possible, one that also contains trace elements.
Soil bacteria are dormant until the soil warms up in the spring; therefore, too early an application of fertilizer in the soil is wasted. Foliar feeding is another option that can be done several times during the growing season as a supplement to your regular fertilization program.
When using package fertilizers, follow the package label as to how much granular fertilizer to apply in April, June, and August. Do not apply any fertilizer containing nitrogen after mid-September. Always water before and after applying granular fertilizer. If dry fertilizer gets on the leaves, rinse it off immediately.
Alfalfa pellets or meal contain a valuable growth hormone and make an excellent organic supplement. Use about one cup per plant worked lightly into the soil in the spring.
Some people use Epsom salt (magnesium sulfate). There is no scientific evidence that Epsom salt serves any benefit for the rose plant. Use very conservatively, if at all, to prevent ground water contamination from runoff.
Fertilizers are of little value if your soil is out of pH balance. A pH range of 6.0 to 6.8 is best for roses. Test your soil occasionally and correct if necessary.
Roses benefit from a yearly organic mulch of two to four inches and weekly deep watering.
Do not fertilize newly planted plants until after their first bloom.