By ROBIN ROBINSON The Key West Garden Club
Diagnosing palm mineral deficiencies is a little like palm reading. They all look alike until the gardener gets down to the details. Barb Smith spoke to the Key West Garden Club's volunteers on Monday morning about fertilizing palms. A palm needs a number of additional mineral nutrients in our poor quality, alkaline soil. Our soil pH is near 7.5, a high alkaline reading.
The latest version of slow release Palm Special contains 8-2-12-4 that is, 8 nitrogen, 2 phosphorous, 12 potassium, 4 magnesium. It is important to use a slow release fertilizer because the water flows quickly through our porous oolite limestone. If it were not slow release, all of the fertilizer would be washed away after the first hard rain.
Palm roots grow horizontal to the ground and can extend 50 feet away from the trunk creating great stability in storms. Because the roots extend so far away from the trunk, fertilizer must be broadcast over a large area to feed the roots. Use 1¬½ pounds over 100 square feet of earth, four times a year.
When a palm lacks of a mineral it is visually obvious. Nitrogen deficiency almost never occurs when palms are planted, but is frequently seen in potted palms. Light green or yellow older fronds indicate a need for nitrogen. Planting grass around a palm will cause an increase in nitrogen in the soil that will destroy the balance of nutrients and damage the palm. Too much nitrogen is bad for the palm. For instance grass, which produces nitrogen, can cause potassium loss. Blame spreads everywhere.
Phosphorous deficits are uncommon unless the palm is grown in a previously planted field that is phosphorous deficient.
Yellow or orange bands on the outer margins of leaves may indicate that the palm is magnesium deficient. Sometimes the problem is so severe that only the rachis remains green. Magnesium loss turns the area between the veins yellow. The remedy for this is to spray with Epsom Salts. Epsom Salts is pure magnesium.
Just like in life, superimposing one problem on another can compound the diagnosis. The palm may also have a potassium deficit if the tip of the magnesium deficient palm is dead, or yellow to orange spots appear or frizzled leaves occur. Fertilizer with high potassium levels can cause magnesium deficit. Mid to lower canopy leaves are most affected.
In addition to the minerals that are provided in Palm Special, lack of other minerals that are vital to the well being of a palm can cause damage. A palm that is deficient in boron will have leaves that fail to open fully. Leaves are damaged four or five months before they emerge crumpled like corrugated cardboard.
Boron leaches from the soil when there is excessive rainfall or over watering. Another symptom of deficient boron is leaf truncation to a V-shape. These palms can live a long time with trunks that are bent sharply to one side. Don't prune the damaged leaves as they are still absorbing nutrients into the trunk. Fertilize with boron.
Leaves appear pale yellow or even white when they are deficient in iron. Older leaves remain green. Iron deficiency occurs due to poor soil aeration or planting the palm too deep in the ground. Iron deficits are common in alkaline soil.
Palms also need manganese to keep them from growing a frizzle top with necrotic streaked, undersized new leaves. They are most severely injured at the base of the leaves unlike potassium deficient fronds that are damaged at the tips of the fronds.
I hope the reader remembers all this material. Key West Garden Club members were threatened with a quiz.
Thursday, April 4 at 1:30 P.M. Constance Miller, herbal practitioner, will be presenting "Local Plants in the Herbal Pharmacy" to the Garden Club Members. The lecture is free and refreshments will be served.
Key West Master Gardener Robin Robinson was a columnist for the Chicago Daily News and syndicated with Princeton Features. Her books "Plants of Paradise" and "Roots Rocks and Rain: Native Trees of the Florida Keys," can be found at the Garden Club and on Amazon.com. This column is part of a series developed by the Key West Garden Club. For more information visit www.keywestgardenclub.com.