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Plant (and maintain) palms like an expert

by Timber Press on March 6, 2018

in Design, Gardening

Sea Crest Nursery, in Santa Barbara, one of California’s premier sources for large, choice palms and cycads, maintains palm specimens in boxes, making them portable and reducing transplant shock in California’s dry, often cool climate. Photographs by Caitlin Atkinson.

Now that you’ve decided to add the iconic silhouette of a palm to your landscape, you’ll need expert advice from Jason Dewees of Flora Grubb Gardens to ensure successful sprouting, planting, fertilizing, and pruning.

Start with a seed. Yes, some palms, such as the commercial date palm, are commonly grown from clonal divisions, but the beginning of most palms is a seed. The general rule for sprouting palm seeds is to soak them for a few days, clean off the outer flesh or husk, and provide consistent moisture and warmth; bright, indirect light; and a well-draining medium. Shift seedlings from their sprouting bed to small containers when they have developed two or three leaves and can still be disentangled from their bedmates without breaking their young roots. Move them up in size before root-confinement slows their growth, but don’t overpot—too much soil volume can retain excess moisture, at the expense of the roots’ need for aeration.

It is time to plant out a seedling once it reaches a large enough size to survive in the ground with regular garden care. For private and protected gardens, that size may be a two-leaf seedling; in a public landscape, it should be larger so as to put up with more potential abuse. Stake if you must to mark and protect the plant. Staking young palms is usually unnecessary, unless the plant is in danger of rocking in very windy sites. Be mindful that leaves may get thrashed if they blow against tall stakes. Shade cloth can help while a young palm roots in, protecting older leaves while new leaves acclimate to higher light.

For all the benefits of starting small—widest choice of species, stronger and speedier growth, growth form that responds to the site, cost savings—palms are attractive to designers as instant trees. They tend to be easier to transplant at large, mature sizes than similar size woody trees because their new roots continually develop from the trunk base—there’s no tap root. It is common to dig palm species amenable to the practice from a field or garden, prune and tie up lower leaves, and transport them to new planting locations. (More varieties are amenable in warm, humid climates where transpiration is lower and growth rates are faster.) There, in a hole about twice the volume of the existing root ball, backfilled with a well-draining medium (preferably horticultural sand), and given a plentiful moisture supply and time, a palm will likely grow new roots and leaves and soon look like a veteran of the site.

When hoisting the tree, installers use a soft—and sufficiently weight-bearing—woven strap (usually nylon), tying it to the best balancing point on the woody trunk (not on any soft tissues); they apply carpet remnants between the trunk and strap for extra protection—any scarring is permanent. Rigging to the box can also work well for some specimens, such as multistem palms. Adding a balanced fertilizer at planting time and then a palm formula quarterly thereafter for the first one to three years will support vigorous growth.

Fruits of an Alexandra palm, Archontophoenix alexandrae, shower into a Hawaiian garden. These eager sprouts require regular weeding, not least because the species is invasive in wet lowland areas of the islands.

Many specimen palms are also grown in containers. The root volume in the box remains undisturbed (though the roots that grow from the box into the underlying ground at the nursery will be lost) when the palm goes to its new landscape. Planting from container bypasses the shock of field-digging and enables a newly planted garden to appear healthy and full from the start. The greater expense yields greater success.

Keep in mind two rules of thumb for planting palms:

  • Don’t cut roots or manipulate the root ball of container-grown palms if this is not necessary—it can set back even the most resilient species and kill sensitive ones. Place the root ball intact in the planting hole, taking care not to drop and shock it. (Resilient species—those commonly planted as field-dug specimens—will likely recover from such root ball disturbance.)
  • Place the plant so that the base of the stem, where new roots emerge (the root-initiation zone), remains below soil grade. In wetter areas, it is important to match the grade to the top of the root-initiation zone—no higher. In drier climates such as those in California, adding 1–2 inches (3–5 cm) of mulch over the rooting zone can be helpful, even if the mulch is touching the stem. No stem should be left on its tip-toes after planting: the base should be snugly in the ground, generally a bit lower than recommended for planting woody trees, with no air or cavity between the base of the stem and the ground.

Fill in air pockets and compact the backfill around the root ball to stabilize the plant. Some species will have aerial roots breaking out of the stem surface well above grade—above the expected rooting zone. It is best not to bury these. In areas with a cool or dry winter, plant palms in spring or summer to take advantage of warm weather and increase chances for success. In tropical areas, plant them at the beginning of the rainy season—which often coincides with spring there.

Palms tend to be heavy feeders. Local soil and climate conditions will determine needs for fertilizer; getting soil tested may be helpful. Cold weather and heavy rainfall can pose nutritional problems. Nurture the soil flora with organic fertilizing and mulching practices if possible—palms take advantage of mycorrhizal relationships in habitat for nutrition and water uptake and can do so in exotic soils with compatible organisms. Four times a year at Flora Grubb Gardens we apply an organic 3-2-4 nitrogen-phosphorus-potassium (N-P-K) formula with crucial micronutrients such as magnesium, calcium, and iron. The most frequent deficiencies we see are of magnesium and potassium, which should be corrected in tandem, lest the plant’s uptake of one element block uptake of the other. Nitrogen deficiency is also common; applying a palm-specific fertilizer is the simplest approach.

A planting with three variations on pinnate leaves: In front, the light green leaves with V-split tips are entire, feather-shaped, with leaflets connected; at center are flat pinnate leaves, with separate leaflets regularly arranged in one plane; and in back are plumose pinnate leaves, with leaflets attached to the rachis in several planes and in clusters. A palm imposter pictured is the banana-like plant with dark green leaves and reddish undersides.

Palms produce a lot of biomass—big, fibrous dead leaves; large inflorescences; fecund infructescences; leafbases often persistent or thorny; or unwanted stems on clustering species. In a manicured landscape, many palms demand regular grooming and pruning to look their best. At the same time, excessive pruning of live leaves in the crown, especially, can harm the form and even the structural integrity of a tree by depriving the bud of the energy needed to develop the natural thickness of its stem, which can narrow and weaken or break. An exception is upon transplanting, when it can be prudent to cut the lower half or more of the crown to reduce wind drag on the newly planted tree. Lower leaves will die off anyway, because the tree loses most of its roots when dug.

Mind this aesthetic directive: cut leaves where the petiole meets the leafbase (or along the node where the leafbase encircles the trunk, skinning the trunk). If cutting any distance out from that point, make sure all the petiole stubs are the same length and as short as possible. Cutting along the leaf blade disfigures the frond. Such partial cuts ruin the arching balance of feather palms, while they blunt the radial expression of fan palms. The unpruned, natural look in established palms, with lower leaves revealing their process of yellowing to straw, can be appealing and wildlife-friendly, but it must harmonize with the landscape context. Burgeoning, untrimmed palms in a stark, modern space may be just the right foil, or they could seem like feral interlopers.

For the healthiest impact, remove only leaves that have turned to straw color; palm trees reabsorb nutrients that remain in their leaves before shedding them. It’s common, if not ideal, to cut the lower half of a crown, including green leaves, to a “nine-o’clock and three-o’clock” position, leaving a hemisphere shape and reducing the frequency of pruning. Use new, sterile tools to minimize the spread of lethal fungal and bacterial diseases. Second best is to cauterize blades or soak them in a solution of one part bleach to one part water after a thorough cleaning. Rinse bleached blades thoroughly with fresh water before cutting.

A happy palm will produce a lot of fruit. Groundcovers can conceal small fallen fruits. When designing plantings over paving or gravel, consider the size and consistency (mushy? dry?) of fruit produced by the varieties of palms under consideration. Consider, too, the maintenance they will require—will it be smarter to remove inflorescences or unripe infructescences, or can the fallen fruit be easily raked up? Pruning before ripening can be more efficient on larger fruiting or seasonally fruiting species; it can be a once-a-year job. Pulpy fruit such as dates take an extra step to remove from paving. Species with hard, rolling fruit might pose a risk to pedestrians. Coconut trees growing anywhere people hang out pose a lethal risk from their 3-pound (1.4-kg) falling fruits. A species growing at the limit of its climate adaptations—or a male plant, or a single female plant lacking a pollinator—might not make any fruit but will perform well otherwise.


Jason Dewees is the staff horticulturist at Flora Grubb Gardens and East West Trees in San Francisco. Responsible for the Tree Canopy Succession Plan for the San Francisco Botanical Garden, he serves on the Horticultural Advisory Committee for the San Francisco Botanical Garden, and on The San Francisco Conservatory of Flowers Advisory Council.


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