Palm trees typically are starving for nutrients, especially in the Lowcountry. While turf gets most of the fertility attention, palms are frequently exhibiting deficiency symptoms that turf fertilizer will not remedy.
Deficiency symptoms may develop on new or old fronds, depending on the nutrient. New leaves emerge from the top of a palm, and the oldest leaves are drooping near the bottom.
Here are some tips:
Palm-blended fertilizers (12-4-12-4) contain nitrogen, phosphorus, potassium, magnesium and micronutrients.
Three to four applications can be made between April and August to promote healthy growth and avoid nutrient deficiencies. However, if palms are still exhibiting deficiency symptoms after fertilization, poor drainage or soil pH imbalance could be the problem. These issues need to be corrected before fertilizers can improve palms.
When everything is in order, granular fertilizer can be broadcast beneath the canopy of the palm. Pull back mulch and avoid piling it against the base of the trunk. If turf is growing up to the palm, fertilizer spikes can be inserted into the soil to reach palm roots. While palm fertilizer products vary, a 12-4-12-4 can be applied at 1.5 pounds per 100 square feet of area beneath the canopy.
It seems that every bit of advice that comes from a horticulturist starts with a soil test. This is no different.
A soil test will reveal two important bits of information: soil pH and nutritional status. Ideal soil pH is 6.5. When that number is lower or higher, it begins to affect the availability of nutrients. Micronutrients are especially affected by a pH above 7. In many cases, correcting the soil pH will solve nutritional problems.
Sandy soils are typically deficient in potassium. This is one of the most common and serious nutrient deficiencies in palms.
While severe potassium deficiencies are not serious in turf or many woody plants, it can be fatal for palms.
Potassium deficiency symptoms start on the oldest leaves with spotting, followed by dead tissue along the margins and tips. As the deficiency worsens, the tips start to fray and frizzle. The midrib, however, stays distinctly greenish-yellow as the foliage around it deteriorates.
High soil pH is often the cause for manganese deficiency, which can be deadly in palms. Manganese is still present in the soil, but the high pH ties it up, making it unavailable.
Manganese deficiency appears as streaking on the newer leaves and eventually can scorch the entire leaf, a fatal condition known as frizzle top. Soil imbalances and drainage issues should be addressed before fertilizer can correct the deficiency. Manganese sulfate can be applied to the soil when needed.
Not to be confused with manganese, magnesium is a macronutrient that will not kill a palm. Magnesium deficiency is primarily visual. Marginal chlorosis begins on the margins of older leaves as bright yellow.
Tip dieback, however, is indicative of potassium deficiency, which often accompanies magnesium deficiency. While Epsom salts contain magnesium sulfate, they are highly soluble and rapidly leach from sandy soils. Magnesium also competes with potassium. so it is advisable to fertilize with both nutrients.
Nitrogen and iron
These nutrient deficiencies are primarily visual and do not threaten the health of the palm. Deficiency symptoms are light green color.
Nitrogen deficiency occurs on older leaves and is accompanied by slow growth.
Iron deficiency starts on new leaves but does not affect growth.
Nitrogen is easy to remedy with fertilizer.
Iron, however, is sensitive to high pH, and iron applications to the soil will not cure the problem until soil pH is corrected.
Tony Bertauski is a horticulture instructor at Trident Technical College. To give feedback, email him at firstname.lastname@example.org.