Issue: June 1, 1996

Lots of brown pine needles

Why are there so many brown needles on my ponderosa pine trees? There are still green needles, but there is also a lot of brown. I thought they were evergreens. Are they dying?

While browning needles in a pine can indicate problems, brown needles are also a natural occurrence. Yes, pines are evergreens. That means there are some green needles throughout the year, but the trees do not keep their needles forever. Most ponderosa pines will dispose of needles which are 3 or 4 years old. This can happen in the fall or the spring. These needles are shaded by the outer, newer, needles and do not receive enough light to photosynthize and produce food for the tree. Pine trees shaded by other trees will also exhibit needle thinning.

Some years there appears to be more brown needles than other years. This is due to the fact that if needles from a good growing year are being dropped, there are many needles to drop. So, if the weather allowed good growth 4 years ago, then this year we can expect a lot of brown needles.

This year was dry in the winter and early summer. This resulted in drying of the new needles. Winter drought causes the needles from the previous year to brown back from the tip. A dry spring can cause tip browning on the new needles. Generally, the base of most of the needles remain green, only the needle tip turns brown. Proper irrigation can reduce this effect. In dry winters, remember to water at least once a month. In dry springs, water well two to three times a month. This irrigation water should be applied beyond the drip line (the end of the branches) over an area which extends outward a distance equal to the height of the tree if possible. Newly planted trees don't have as extensive a root system and can be watered at the base of the tree for the first two to three years, then the water placement should be moved outward.

If all the needles at the tip of a new branch turn brown, then a problem is indicated. You might have a pine tip moth infestation. In this case, the twig will be hollowed out by the insect. You can break the tip of the twig to check this. If you aren't sure contact your local county agent for assistance. If pine tip moth is the problem, taking a sample of the affected branch to the County Extension Office will allow them to diagnose the problem. However, a branch off a tree will not always be sufficient if the culprit is not present in that branch. Some problems originate below the location at which you observe the problem. Pine bark beetle can cause browning of the needles as it attacks the trunk of the tree, but in the case of the bark beetle, all the needles will die suddenly.

Your problem is probably just the natural dropping of needles if there are green needles at the ends of the branches. This year you will probably find that many of these needles have turned brown at the tip of the needle. Don't worry unless needles at the tip of the branch or all the needles on the tree turn brown.

Keeping a cold frame "just right"

can I keep my coldframe from becoming too hot? All of my plants have burned up.

oldframe, especially in New Mexico, must be ventilated on sunny days. Even when the temperature is below freezing outside, the temperature inside a cold frame can climb quite high once the sun hits it. Place a thermometer inside the coldframe and open the lid when the temperature climbs to 70 degrees or so. If it is freezing outside, be careful not to open the lid too much. If it is cloudy, windy, or a cold front is expected, be careful to monitor the temperature after ventilating the coldframe.

Some gardeners place plastic jugs filled with water in the coldframe between the plants. These water-filled jugs will absorb heat and slow the rate of temperature increase in the cold frame. At night or when a cold front passes, they will release the heat, protecting the plants. Painting the jugs black will increase their ability to absorb the heat in sunlight.

It is also possible to buy automatic coldframe/greenhouse vents. Some of these operate by expanding a gas in a cylinder as they warm and require no electricity. As the cool, the gas contracts and closes the vent. You might want to consider these as well, but watch them closely to be sure they don't malfunction.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!