Another Take on Responding to the Recent Palm Horticulture Questions

Donald R. Hodel and Robert H. Burtscher

Here we offer our response to the recent horticulture questions about the best time of year to plant palms and watering and fertilizing them.

Is Spring the best time to plant palms?

Generally, Spring is the best time to plant palms (planting out of a container resulting in little root disturbance) because planting at this time gives the palm as many months as possible for active growth to become established before the onset of winter, which is especially important for tender, marginal palms. On the other hand, tough, cold hardy palms like Canary Island date palms and Washingtonias can be planted year-round in Southern California.

However, to transplant palms (digging them up and moving them, resulting in lots of root disturbance) spring is the best time for all species of palms.

Palms planted or transplanted later in the season, like summer through winter, will not grow much if at all until Spring, several months away. The palm just sits there in the cold and perhaps moist environment, making it susceptible to numerous secondary problems like disease, pests, and nutrient deficiencies.

Do newly planted palms need more water than established palms?

The answer to this question depends on several variables. Also, what does “more” mean, more in quantity or more in frequency, or both?

Generally, newly planted palms (planting out of a container resulting in little root disturbance) need to be watered more frequently than the same-size palm in the ground because their roots have yet to extend out into the surrounding site soil and the plant has a very finite and restricted soil mass and root system (no larger than the container from which the plant was grown) to hold and take up water; it can potentially dry out quickly compared to a plant of the same size already established in the ground and that has a larger soil mass and more extensive root system to hold and take up water. Imagine a well rooted palm in a 5-gallon container; if it was necessary to water it twice a week prior to planting it out, you will still have to water it twice a week after planting it out, at least until its roots extend out into the site soil where they can access more soil and water.

For transplanted palms (digging them up and moving them, resulting in lots of root disturbance), which have typically had leaves or portions of leaves removed and the remainder tied up to prevent water loss (a standard practice when transplanting palms in hot dry areas), less water might be necessary when compared to an already established palm of similar size.

If some leaves are not removed and the remainder not tied up during transplanting, a little less water might still be necessary compared to a palm of equal size established in the ground, at least initially, because not as many roots or functioning roots will remain to take up the water so the root zone will not dry out as fast.

In either case, the objective when watering planted or transplanted palms is to check the original root ball, backfill, and surrounding site soil, and whichever of these three dries out first (usually the root ball), it is then time to water all three. For how much and how often to water, see the last question.

Do you fertilize newly planted palms?

The answer to this question depends on several variables. Newly purchased containerized palms might already have sufficient nutrients in the soil so they do not need to be fertilized immediately. But if you know the palm has not been fertilized in a while, then fertilizing at planting time is perfect. Dig the hole as deep as the root ball and twice as wide, put the recommended about of fertilizer (palm special type high in nitrogen, potassium, and magnesium with micronutrients and all in a timed-release formulation) in the bottom of the hole and cover with a quarter inch of soil (the roots will grow into the fertilizer), place the palm in the hole, backfill with the same unamended soil that came out of the hole, tamp firmly, cover with 2 inches of mulch from the trunk out for two to three feet, and water well.

How often do you water?

This question should be how often and how much do you water established palms in the ground, which depends on several environmental factors, the most important being temperature, exposure to sun (solar radiation), wind, time of year, and soil type. The general objective is to water deeply, pushing water to at least 12 inches deep at each watering episode, but as infrequently as possible to encourage a deeper root system.

Generally, water palms when they need it. How do you know when they need it and it is time to water? It is best to water when the upper foot of the root zone loses about 50% of its available water (generally when the soil dries out 2 inches below the surface). Look at and feel the soil and when the root zone dries out 2 inches below the soil surface, it has lost about 50% of the water and it is time to apply water.

Now that you know when to water, you need to determine how much water to apply, which depends on your soil type. Light soils like sand hold about 1 inch of water per foot, loam soils hold 2 inches of water per foot, and heavy clay soils hold about 3 inches of water per 2foot. So, when half of this water is lost through the plant and by evaporation from the soil (0.5 inch on sand, 1 inch on loam, and 1.5 inches on clay), it is time to water and reapply the 50% that was lost. So, when the soil 2 inches below the surface dries out, apply 0.5 inch to a sand soil, 1 inch to a loam soil, and 1.5 inches to a clay soil.

How do you know how much water your system is applying?

If you have sprinklers, set out 10 or so straight-sided, flat-bottomed cans (tuna fish or cat food) in your irrigated area, run the system for 15 minutes, then measure the depth of water in the cans. Take an average, multiply by four, and that will give you your rate in inches per hour. Now you know how long to run your sprinklers to apply the desired amount of water.

If you have drip irrigation system and emitters are 12 inches apart, and because emitters generally put out about 1 gallon per hour, the system would theoretically cover about a 12- inch square of soil with about 1.5 inches of water (it’s actually a bit less than that because of uneven distribution due to poor lateral movement of the water). Thus, it is an easy calculation to figure out how long to run the drip system to apply the desired amount of water.

After a while of looking at and touching and feeling the soil, you might develop a sort of sixth sense about when to water, but it is always a good idea visually and touch and feel the soil to check the moisture content. Also, keep in mind that to apply through a sprinkler system much more than 0.5 inch of water to a loam or clay soil at one episode runs the risk of wasteful run-off, especially if the ground is sloped. To mitigate runoff when using a sprinkler system, you might have to apply the desired amount of water in cycles. For example, if you have to apply 1 inch of water, you could apply it at two 0.5-inch cycles with an interval in between to allow for a slight dry down.