TropicLine Volume 7, Number 1, January-February, 1994
Editor: Alan W. Meerow
Christine T. Stephens, Dean, Cooperative Extension
Removing Potassium-deficient Leaves Accelerates
Rate of Decline in Pygmy Date Palms
Timothy K. Broschat
Potassium deficiency is a widespread and often serious
disorder on many species of palms throughout the world
(Chase and Broschat, 1991). Potassium is mobile within
plants and deficiency symptoms are most severe on the oldest
leaves, becoming less so on younger leaves (Mengel and
Kirkby, 1982). As K deficiency becomes more severe on palms,
the symptoms will affect progressively younger leaves until
no symptom-free leaves remain. At this point, if untreated,
new leaves will emerge chlorotic, reduced in size, and with
extensive necrosis. Death of the palm's only shoot meristem
often follows (Broschat, 1990).
Leaves normally remain on a healthy palm for 2 or more
years, depending on the species, and each palm will retain a
species-specific number of leaves (Tomlinson, 1990). Mildly
K-deficient leaves are typically removed during landscape
maintenance because they are visibly discolored, and
severely deficient leaves appear dead except for the rachis
and adjacent areas of the leaflets. Under conditions of K
deficiency, K from the oldest leaves will be mobilized for
use by the newly expanding leaves. Premature removal of the
oldest K-deficient leaves may remove a source of K needed
for plant growth. Potassium required for continued growth
should then be mobilized from the oldest remaining leaves,
which may previously have been symptom-free. As these leaves
become symptomatic and are subsequently removed, still
younger leaves will be utilized as a source of K by the
meristem. Thus, removal of K-deficient leaves may accelerate
the rate of decline from K deficiency in palms. The purpose
of this study was to test this hypothesis on pygmy date
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palms (Phoenix roebelenii O'Brien), a species highly prone to K
deficiency and which matures at a small enough size to be
easily grown in containers.
Mature pygmy date palms having gray trunks at least 30 cm
long were transplanted from 24-liter containers into
38-liter polypropylene containers using a 5 pine bark: 4
sedge peat: 1 sand medium amended with 880 g MicromaxR and
4.9 kg of dolomite/m3. Mild K deficiency occurred on palms
fertilized with 200 g of Osmocote 17N-3P-10K per container
every 6 months and moderate K deficiency was induced by
fertilizing with 160 g of Osmocote 17N-3P-10K and 40 g of
Osmocote 40N-0P-0K plus 20 g of MgSO4.H20 per container.
Within each fertilizer treatment, 10 replicate palms had
only dead leaves removed every 3 months, and 10 had dead as
well as K-deficient leaves removed on the same time
interval. A leaf was considered deficient if more than 3
leaflets had tips with 1 cm or more of orange discoloration.
Palms were grown under full sun (max. PPF=2100 uE.m2.sec-1)
and received water as needed from rainfall and overhead
irrigation. After 18 months the number of dead, deficient,
and green leaves per tree were counted, and leaf samples
consisting of the central 10 leaflets from the most recently
matured leaf and the second oldest living leaf on each tree
were collected for nutrient analysis. Leaf samples were
dried, ground, and digested using a modified sulfuric acid
and hydrogen peroxide procedure (Allen, 1979), with K
concentrations determined by atomic absorption
spectrophotometry. Data were analyzed by analysis of
Both mildly and moderately K-deficient palms having
deficient and dead leaves trimmed had significantly fewer
green non-symptomatic leaves than those having only dead
leaves removed (Table 1). These results support the
hypothesis that removal of K-deficient leaves results in
reduced canopy size and an accelerated rate of decline from
K deficiency. In addition, significantly fewer dead and
deficient leaves remained on the moderately deficient plants
if both dead and deficient leaves were removed when compared
to plants with only the dead leaves removed (Table 1).
For mildly deficient palms, only the number of dead leaves
was reduced by removing both deficient and dead leaves
compared to removal of only dead leaves. For both trimming
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treatments, the number of green leaves retained by
moderately deficient palms was less than for the mildly
deficient palms of the same leaf removal treatment (P<.05),
suggesting that the number of green leaves retained may also
be related to the amount of K in the soil available to the
When both old and recently matured leaves were analyzed for
leaf K concentrations, no significant differences existed
among any treatments (data not shown). It appears that as
long as older leaves are available to supplement K taken up
from the soil, the K content of recently matured leaves will
remain relatively constant until all leaves are deficient.
Similar results were reported for K-deficient African oil
palms (Elaeis guineensis Jacq.) (Hartley, 1988). Assuming that
K is mobilized at a constant rate from oldest leaves under
conditions of similar K deficiency, the K concentrations in
the second oldest leaves should also be equivalent,
regardless of the number of green leaves above it in the
In conclusion, canopy size (green leaves, as well as total
living leaves) was reduced after 18 months of K deficiency
in pygmy date palms when deficient leaves were periodically
removed, compared to palms from which only dead leaves were
removed. This supports the hypothesis that removal of
deficient leaves removes a significant source of K for the
growing meristem and accelerates the rate of decline from K
Allen, S.E. (ed.). 1974. Chemical analysis of ecological materials.
Blackwell Scientific Publ., Oxford, England.
Broschat, T.K. 1990. Potassium deficiency of palms in south Florida.
Chase, A.R. and T.K. Broschat (eds.). 1991. Diseases and disorders of
ornamental palms. Amer. Phytopath. Soc. Press, St. Paul, MN.
Hartley, C.W.S. 1988. The oil palm. Longman Sci. and Tech., Essex, England.
Mengel, K. and E.A. Kirkby. 1982. Principles of plant nutrition. 3rd ed.
Intern. Potash Inst., Berne, Switzerland.
Tomlinson, P.B. 1990. The structural biology of palms. Clarendon Press,
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Table 1. Effects of periodic trimming of K-deficient leaves over an 18-month period on the
canopy structure of mildly- and moderately-deficient pygmy date palms.
Treatment No of Leaves
Green Deficient Dead
)i/ 70 1 7
I )cI! Ie'ek'\ I /Il. /
"k't /U 12 () 1' 10( 5
Si,,nificance (Pi 02 NS 0001
Dead and deficient 18.4 9.1 0.2
't/'//v1 /2/ 4 7 27 7 1 3
Significance (P) .02 .001 .0002
Nursery Production of Pickerelweed
Nursery Manager, Conservation Consultants
David L. Sutton
Professor, Aquatic Plants
Pickerelweed (Pontederia cordata L., family Pontederiaceae), is
a perennial, emergent, aquatic plant. Three common varieties
of pickerelweed have been identified: Pontederia cordata L.
var. cordata, Pontederia cordata L. var. lancifolia (Muhl. ) Torrey,
and Pontederia cordata L. var. albiflora Raf.
Pickerelweed is found in
all sections of Florida,
but is more abundant in
cerLtral and south Florida.
variety cordata has a
glabrous floral tube that
is shaggy pubescent in the
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bud stage. The leaf blades
are deltoid-ovate to
triangular lanceolate with
bases deeply cordate to
b truncate. It ranges from
SSouth America to Ontario,
Canada, including much of
the Eastern United States.
Variety lancifolia has a floral tube that is persistently
pubescent with glandular hairs. The leaves are narrowly to
broadly lanceolate with bases typically unlobed. It ranges
from South America and the West Indies to Tennessee,
including the Southeastern United States.
A third variety, albiflora, has white flowers. It is found in
areas around Louisville, Kentucky, and in Pinellas County
and the basin marsh of Paynes Prairie in Florida.
All three varieties of pickerelweed occur in streams,
marshes, ditches, swamps, ponds and lakes in up to 3 feet of
water. When pickerelweed plants are planted in lakes, they
become established in water from 3 inches to 2 feet in depth
if they are not submersed. These plants grow well in
sediments high in nutrients and spread quickly to cover the
Pickerelweed grows in a wide range of water quality. It may
completely fill small ponds and drainage ditches, even to
the point of impairing water movement. It spreads from seed
and also vegetatively from creeping rhizomes rooted in the
substrates. It flowers year round if not frost damaged, but
most flowers are formed in summer and fall. Seed may be
collected after the pollinated flower spike has bent
downward. Mature seeds will shatter from the flower stalk.
Field observations indicate that the best time to germinate
pickerelweed seeds is from April through July. However, the
germination of pickerelweed seeds collected from plants
growing in temperate climates may be somewhat different from
those collected in Florida as seeds from cooler regions
require a period of moist, cold storage before they will
Nursery production of pickerelweed may be accomplished with
seeds or vegetative material. A root section approximately
1.5-inches in length is suitable vegetative material. These
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may be collected from field sites. Uncut roots remaining in
the ground send up new shoots within 3 to 4 weeks during the
summer growing season. The seedlings or root sections may be
cultured in potting soil in standard 2-, 4-, or 6-inch
commercial pots. The use of sand amended with commercial
fertilizer is one way to culture weed-free plants.
One of the problems involved in planting nursery container
grown plants is the height of plants in relation to water
depth. Small pickerelweed plants submersed at the time of
planting or within a few weeks afterwards generally die. It
is important to be able to grow tall nursery plants. One way
of doing this is to use 2-inch square by 6 inch deep pots.
Of course, large plants will require more production space,
fertilizer, etc., and will be more difficult to transport
than smaller plants. But the increased survival of large
plants will help offset the need to replant those that die.
Nursery grown plants may be damaged by leaf miners in the
leaves or mealybugs on the roots. An insecticide, such as
malathion, may be necessary to control these pests. When
plants are grown in the same container over a prolonged
period of 120 to 180
days, the older leaves
die and may cause
disease in the stems
just above the roots.
The old leaves need to
be removed to prevent
Tissue culture is also
being used for
pickerelweed. One of
the top priorities of
the future is to grow
as many plants as possible from seeds, vegetative material,
or tissue culture to reduce the number of mature plants
harvested from wetlands. Commercial production of
pickerelweed will help preserve natural wetlands. This is
important because it takes many years for a man-made wetland
to perform the same function as a natural one. Pickerelweed
is one of the most commonly used aquatic plants for
mitigation, shoreline restoration, and roadside revegetation
projects. Pickerelweed is also used for water gardens and
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ponds in home landscapes as well as indoor aquaria.
Lowden, Richard M. 1973. Revision of the genus Pontederia L. Rhodora
Sutton, D. L. 1990. A method for germination of arrowhead, pickerelweed,
and spikerush seeds. Aquatics 12(4): 8-10.
Sutton, D. L. 1991. Culture and growth of pickerelweed from seedlings. J.
Aquat. Plant Manage. 29: 39-42.
Whigham, D. F. and R. L. Simpson. 1982. Germination and dormancy studies of
Pontederia cordata L. Bull. Torrey Bot. Club. 109: 524-528.
Aquatic plant images provided by the Information Office of the University of Florida, IFAS, Center for
Aquatic Plants (Gainesville)
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