Download Yellowing in the garden - Charlotte County Extension Service

Yellowing in the garden
By Ralph E. Mitchell
While it is nice to see yellow flowers in the garden or even plants with naturally golden
foliage in the landscape, yellowing as it relates to plant problems is often not a good
thing. Yellowing leaves may be a sign of a lack of nutrients, soil pH problems or even
old age. What are yellowing leaves telling us and how can we correct this condition?
First of all, some yellowing of leaves is normal. I cannot count the number of times
people have asked about yellow leaves dropping off of various plants such as gardenias
and hibiscus. Some gardeners perceive that all of our evergreen sub-tropical to tropical
plants are perpetually in full leave at all times. Yellow leaves are seen by some as a
danger sign and falling yellow leaves really sounds the red alert! Physiological leaf drop
is perfectly normal and expected of the older, lower leaves. While it seems to be a very
seasonal, cyclical occurrence, it can illicit cause for concern. I generally tell people that
if they see older, lower leaves nearer the trunk that turn yellow and drop, this is not much
of a concern. Real trouble may be brewing if leaves drop that are green or if new leaves
are yellow. While it may be easy to differentiate the term evergreen from deciduous (a
woody plant that seasonally drops all of its leaves) keep in mind that even old evergreen
leaves wear out and drop from time to time.
Once normal leaf yellowing has been excluded, nutritional deficiencies can be
investigated. It is not uncommon to see acid-loving plants such as ixoras, gardenias and
hibiscus develop yellow leaves sometimes with the leaf veins remaining green. This may
be a sign of an iron and/or manganese deficiency. Bahia grass also has a tendency to
yellow due to iron deficiencies. Our very sweet, highly alkaline soils are often to blame
as they biologically lock-up certain nutrients when the pH is too high. The nutrients may
actually be present, but are chemically not available for plants that prefer an acid soil.
There are a number of ways that we can solve this problem.
It would be great if we had naturally acid soils that the plants could happily grow in.
Some pre-plant considerations could help. Try not to plant acid-loving plants too close to
concrete walkways or foundations. The concrete can make the adjacent soil very
alkaline. Also, don't use stone mulch with these plants as this can also contribute
alkaline materials which will raise the soil pH. While elemental sulfur is often used to
lower the soil pH to the benefit of acid-loving plants, the effort is often short term and is
generally futile. The alkaline condition of our residential soils will, with time, neutralize
the soil back to a high pH.
Often the best solution is to use what are called chelates. Chelated iron and or
manganese are designed to work in alkaline soils to help correct deficiencies. While this
may be applied according to label directions as a granular product; some are formulated
as a foliar spray for even quicker results. These chelated materials, available at most
garden centers, are biologically available to the plant and do the job.
For more information on all types of plant nutrient questions, please contact our Master
Gardeners on the Plant Lifeline at 764-4340 from 1 p.m. to 4 p.m. Mondays, Wednesdays
and Fridays. Our office is located at 25550 Harborview Road, Suite 3 in Port Charlotte.
Our Plant Clinics are available across the county:
Demonstration Garden every Thursday from 9 to 11 a.m.
Englewood/Charlotte Public Library 9 a.m. to noon every Monday.
Mid County Regional Library first and third Thursday of the month from 1 to 3 p.m.
Monthly Plant Clinics are Saturdays from 9 a.m. to noon at the following
locations: Cape Haze Publix first Saturday of the month;
Peachland Promenades Publix ‹ second Saturday of the month;
Home Depot Murdock and Home Depot Punta Gorda the third Saturday of the month
Ralph Mitchell is the county extension director/horticulture agent for the Charlotte
County Cooperative Extension Service. You may contact him
by e-mail [email protected] You may also contact a volunteer
Master Gardener from 1 p.m. to 4 p.m. Monday, Wednesday and Friday at
764-4340 or by e-mail [email protected]
Resources:
Simone, G.W. (1999) Mistaken Identities for Plant Diseases, The University of Florida
Cooperative Extension Service, IFAS.
Keeler, G., Gabel, K. & Schoelhorn, R. (2003) Ixora for South Florida. The University of
Florida Cooperative Extension Service, IFAS.
Trenholm, L. E., Cisar, J. L. & Unruh, J. B. (2003) Bahiagrass for Florida. The
University of Florida Cooperative Extension Service, IFAS.
Bradshaw, J. (2003) Gardenias. The University of Florida Cooperative Extension Service,
IFAS.
Ingram, D. L. & Rabinowitz (2003) Hibiscus in Florida. The University of Florida
Cooperative Extension Service, IFAS.