Rose Culture

Fertilizer basics

Fertilizing is synonymous with production in roses. Plants must be fed if they are to remain healthy and produce good blooms. You must return to the soil quantities of nutrients equal to those being consumed by the plant.

Strictly speaking, there is no such thing as an organic fertilizer. Organic materials feed the soil bacteria, and they in turn break it down into inert mineral salts, the only form in which the plant is capable of absorbing them. However, organic materials are essential for a well-conditioned soil.

Chemical fertilizers are generally faster-acting than organic materials, since they require only dissolution in water to become available to the plant.

All products labeled as fertilizer must, by law, have 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 blooms; while potassium or potash stimulates the general health of the plant.

Always water well before and after an application of granular fertilizer. If dry fertilizer gets on the leaves, rinse it off immediately.

Soil bacteria are dormant until the soil warms up in the spring; therefore, too early applications of fertilizer in the soil are wasted. However , some benefit can be obtained by foliar feeding plants with a water-soluble plant food during a cool spring.

If a granular commercial fertilizer is used, choose one with a general balance between the three main chemical ingredients and, if possible, one that also contains trace minerals.

One to two handfuls of granular fertilizer applied in April, June, and August will suffice. Avoid applying any fertilizer containing nitrogen after early September.

Osmocote™ and other time-released fertilizers can be applied to the soil at pruning time and will adequately feed the plant for the entire growing season. However, most Rosarians will supplement this with occasional granular or water-soluble fertilizers.

Alfalfa pellets contain a valuable growth hormone and make an excellent feeding supplement -- about two cups per plant worked lightly into the soil in the spring. (Use only pellets or meal with no added salt.)

Epsom salts (magnesium sulfate) is also useful to the plant if you are not regularly applying dolomite lime (which contains magnesium sulfate). Approximately 1/3 cup per plant in the spring is recommended at least every other year. (If dolomite lime is applied once or twice yearly to rosebeds, this will provide the needed magnesium, and no Epsom salts need be added.)

Fertilizers are of little value if your soil is out of balance. A pH range of 6.0 to 6.8 is best for roses. Here in the western Pacific Northwest, soils tend to be acid and may need an addition of lime to be with the needed range. Test your soil occasionally and correct if necessary.