Browning Needles We get a great many questions about conifer health here at the Henderson County Extension Center. By conifers we mean the cone bearing plants such as pine, cypress, juniper, arborvitae, etc. These plants are planted all over the county by the thousands and valued by gardeners.
One question is 'why are the needles on the interior of my conifers turning brown'? In short the answer is browning needles in the interior of conifers is a natural part of the tree getting larger and older. The browning of the interior needles of conifers is a natural process and nothing to be worried about.
The Christmas Tree Shape is a Juvenility Feature Conifers such as pine, cypress, cedar and arborvitae start out as young Christmas tree shaped plants. These young evergreen trees have limbs all the way to the ground. They have needles extending into the interior of the plant.
As the plant gets larger, upper limbs begin to shade lower limbs. The interior of the plant gets shady. Since the only reason for a needle to exist is to gather sunlight, the plant stops supplying the needles in the shade with nutrients and water and the needles turn brown.
Moisture is the Enemy of Many Conifers Conifers are not easy to grow in the warm humid environment of western North Carolina. Most conifers like well-drained soils and dry air. In western NC, the land of rain, these plants stay too moist for too long and get various diseases.
Shade Conifers need full sun!!! Six to eight hours of sun is required for healthy conifers. Sun helps dry out plants after rains. Conifers planted in the shade exacerbates the wetness problem. Increasing air flow through pruning in and around conifers helps them dry out as well.
Dwarf conifers are dense and do not dry out quickly after rain events. Dwarf plants are genetically anomalous and therefor often not the most robust plants. Really densely branched plants hold onto water after rains. Dying leaves on the interior of dwarf conifers can build up and lead to problems. Clean out from under dwarf conifers to increase airflow.
Heavy pruning that is used for topiary or hedging just creates wounded branches and needles during the summer when diseases are most prevalent. Conifers should not be pruned during the growing season. Limit pruning to the cool season when insects and diseases are dormant.
Planting Conifers in Hedges Gardeners should avoid planting conifers too close together. Conifers planted too close together can rapidly outgrow their soil space and run out of nutrients. A plant will take nutrients from older less productive leaves and move the nutrients to the outer newer more productive needles. In the case of conifers the new leaves at the end of the branches take nitrogen from the inner needles.
Plant Leyland and Murray cypress, 'Green Giant' arborvitaes and other large conifers at least 15 feet apart; 25 feet would be even better. Finally, make sure your conifers get full sun all day and plenty of water and fertilizer. Conifers do not like saturated soils but they need adequate water during drought.
Fungicides If you have a large investment in lots of conifers it would be a good idea to spray the plants with a copper based fungicide according to labeled instructions throughout the spring and summer annually. It can be purchased in most garden centers and ag supply stores.
