Experts tackle readers’ garden questions.
Q: Between 1994 and 2008, I planted eight fern pine trees – small leaf variety – around the perimeter of the house. About two to three summers ago, I first noticed what seemed to be unusual leaf “die-off” in the crown of a tree planted in 2000. Since then, it appears to have increased and the same thing is now occurring in two other fern pines planted in 1994 and 2002. The five remaining trees, planted between 1994 and 2008, show no signs of the problem as of now. I deep water these trees for two hours every three to four weeks during the summer. Is this leaf die-off some sort of bug infestation and, if so, is there any treatment available? Is this problem heat or drought related? Am I not watering enough?
William Van Dyck, Sacramento
Sacramento County Master Gardener Linda O’Connell: Fern pine (Podocarpus gracillior) is a versatile evergreen plant grown for its attractive foliage and interesting form. Fern pine is a native of east Africa, where it grows to 70 feet tall.
In California, fern pine trees can grow 20 to 60 feet tall and spread 10 to 20 feet wide at maturity. This plant is among the cleanest and most pest-free choices for home planting, and can be used as a street or lawn tree, or as an espalier, hedge, large shrub or container plant.
Fern pines will grow in full sun or partial shade, and will tolerate a wide range of soil types. However, the tree needs well-drained soil, and may display signs of chlorosis (yellowing leaves due to a lack of chlorophyll) in alkaline, heavy or damp soils.
Because your three trees began their decline during the drought, it is possible that lack of water is at least part of the problem. Mature fern pines will tolerate drought conditions, but require water when the soil is dry in the top two inches. Inadequate water causes foliage to wilt, discolor and drop.
Are the trees planted in or near lawn? If so, it is possible that the tree roots are receiving too much water during lawn irrigation. Prolonged moisture and poor drainage will result in smaller leaves, dieback or limb drop, and susceptibility to root rots, mineral deficiencies or toxicities, wood-boring insects and other pests that eventually can kill plants. Excessive moisture smothers and kills roots. As roots die, discolored and dying foliage appears in the above-ground portion of the plant.
Tree roots extend beyond the dripline (or outer edge) of the tree’s canopy. In heavy clay soils, lateral roots may grow one and a half times wider than the tree’s canopy. In sandy soils, roots often grow up to three times wider. A study conducted by the University of California (UC) Cooperative Extension found that roots can extend far beyond the tree’s dripline – up to 39 feet in one orchard.
Deep watering every three to four weeks should be adequate if the water is getting to the root zone and to a depth of two to three feet. If your trees continue to show die-off after making necessary adjustments to your watering method, you may want to increase or decrease the time of each watering to see it this makes a difference. Check to make sure the soil is dry before watering by using a soil probe tube.
In general, fern pines are resistant to most pests and diseases, but can be susceptible to aphids, scale and sooty mold. For more information on pests and disorders common to the fern pine, visit the UC Integrated Pest Management website at ipm.ucanr.edu.
Hopefully, your efforts will prevent the other five trees from showing signs of die-off.
Linda O’Connell is a UC Cooperative Extension Master Gardener with Sacramento County.
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