Fertilizing Roses
Most roses need regular applications of fertilizer to reach their
full size and produce abundant flowers. A healthy, well-fed plant is
also better able to resist attacks of pests and diseases and to survive
severe winter cold.
The rate and frequency of fertilizer application and the appropriate
fertilizer to use depend on the type of garden soil. Plants in sandy
soil need frequent applications; those in a heavy soil may not need as
many. A soil test will help determine the particular balance of the
three major nutrients—nitrogen, phosphorus, and potassium—that your
garden needs. The staff of a local nursery can often recommend the
fertilizer ratio and application rates for your area.
Kinds of Fertilizers
Both natural organic and synthetic fertilizers are available in dry or
liquid preparations. Organic fertilizers, derived from plants and
animals, act more slowly and need microorganisms to break them down into
elements usable by roots. Synthetic fertilizers act on the plant more
quickly; they must also be reapplied more frequently.
Dry fertilizers are worked into the ground and are spread to the roots
by watering. Liquid fertilizers are added to water and usually applied
to the roots. Foliar liquid fertilizers are sprayed onto the leaves,
which absorb the nutrients.
Many rose gardeners rely on a complete (meaning that it contains
nitrogen, phosphorus, and potassium) dry fertilizer and supplemental
applications of a liquid fertilizer. Moisten the soil before you apply a
fertilizer; water again after you've applied it to carry the nutrients
to the roots. Do not spray fertilizer on foliage on hot (over 85° F)
days. Whatever kind of fertilizer you use, always follow exactly the
directions and the dosage recommendations on the product label.
Excessive doses of fertilizer can severely harm a plant.
Frequency of Application
 Species roses, old roses, and climbers usually need only one application
of fertilizer in the early spring as the buds prepare to burst.
Remontant (repeat-blooming) old roses and climbers will benefit from a
second feeding of liquid fertilizer after the first bloom.
Modern roses need regular feeding to provide energy for growth and
blooms. Begin fertilizing newly planted roses once they are established,
about three to four weeks after planting. Start fertilizing older plants
after they have been pruned and the new foliage starts to appear.
There are two schools of thought on the frequency of subsequent
applications. Some gardeners favor applications of fertilizer every six
to eight weeks, or three or four times, during the growing season. Other
gardeners swear by applications every three to five weeks, usually
alternating dry and liquid fertilizers in reduced amounts. Both
recommendations are based on using synthetic, fast-release fertilizers.
Fast-draining sandy soil benefits from the more frequent applications.
You'll probably want to experiment and see which method works best for
you.
In regions where winter temperatures drop below 10° F, stop applying
fertilizers that contain nitrogen six weeks before the anticipated first
frost, and apply instead a fertilizer containing only phosphorus and
potassium to strengthen the plant for the winter.
Iron-Deficiency Chlorosis
Chlorosis is an unnatural yellowing of foliage. Iron deficiency causes
interveinal chlorosisthe tissue between the veins turns yellow and the
veins remain green. This condition is caused by a shortage of iron
available to the plant as a result of poor drainage, excess lime in the
soil, or a naturally alkaline soil. Preparing the planting site
properly, using the results of a soil test, is the best prevention.
Roses with some yellow or orange shading in the petals are most
susceptible to iron Chlorosis. Spraying the leaves with a solution of
chelated iron fertilizer will take care of mild cases. For severe cases,
improve the soil by working in iron chelate fertilizer around the plant
according to label directions; improve the drainage.
Fertilizing Roses in Containers
Because roses grown in containers are watered more often and nutrients
are thus leached from the soil at a faster rate, these plants need more
frequent applications of fertilizer. Whether you are using dry or liquid
fertilizer, a good rule of thumb is to halve the recommended dosage and
apply it twice as often as directed on the label. Again, don't
overfertilize. If you mistakenly apply too much, give the plant several
thorough soakings of water to wash the excess fertilizer out of the
soil.
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