: I have several Carolina cherry trees. Some are doing wonderfully while others show various signs of distress. They are all on the same 30-minute, daily watering schedule. The soil here is quite sandy and the only the compost soil was added at planting about eight years ago. Additionally, I have annual deep-root fertilization done in the spring.
A: Thanks for including the pictures. It helps. What I see is typical leaf scorch from excessive water loss.
My first reaction was that they were getting too much water, which was possibly causing root rot and leaf scorch. But with the type of soil you have and the lack of soil amendment, it is possible they may not be getting enough.
Water is lost from the leaves at such a rapid rate and in such volumes that the leaves cannot keep up so the parts of the leaves furthest from the veins (which carry the water) first yellow and then turn brown and die.
The answer may not be to simply apply more water. We have to consider the plant first. This particular plant does not do well in real hot locations where water loss is extremely high.
One possible answer might be that it is in the wrong spot. It might just be too hot for it in that location.
Another possibility could be plant health. I noticed in the picture that your trees are planted in rock mulch. Two problems occur for this plant in this environment.
First, a lot of heat comes off of the rock. Rock surfaces in midsummer will be about 170 degrees F and this kind of heat radiated back to the trees can be quite damaging.
Secondly, soils covered with rock become “mineralized” over time. When the plant is first put into the ground, it is frequently planted with some type of soil amendment, as yours was. Over a period of a couple of years, this soil amendment breaks down and disappears. Once it is gone there is nothing left to replace it. The steady loss of organic material with no replacement causes the soils to become dominated by soil minerals.
Organic amendments help to keep soils open, retain water and provide for the movement of water into and through the soils. As these amendments disappear, the soil slowly “closes” to air and water movement.
Next, organic matter helps lower soil pH and adds natural chelates that help many minerals be more “available” to plants. Without proper nutrition, the plant loses its good health and tolerance to hostile locations.
My gut tells me your trees are in the wrong spot in the yard, but you can use organic surface mulches to help the soil retain water. You could use a soil moisture meter to help you determine when to schedule the next irrigation. These can be bought for about $7 at a local nursery or garden center. You do run the risk that if you apply water more often, you could kill the trees due to root rot.
Q: I live on a large property in the northwest part of the valley. I have more than 20 Mondale pines growing throughout my yard. These pines range from seven to 10 years old and 20-30 feet tall.
They have been great trees for the last 10 years, but over the last few weeks they have started to lose their needles at a rapid rate. Some of the smaller branches have died back. On some of the trees, about 6 inches of the tips of the branches are dead. I have not changed my watering schedule nor used any different kinds of fertilizers or pest control. Do you have any idea what is going on? Is the dieback normal for this time of year?
A: The problem is most likely related to water. Usually the loss of needles in pines means not enough water. This can translate into not giving the trees enough water, not applying water often enough or both. It also might mean that the water may not be applied in a large enough area surrounding the tree.
By applying water over a larger area under the tree we effectively increase the amount of water available to the plant. Whenever water is applied to trees, it needs to penetrate to a depth of 18-24 inches. Drip emitters, because they deliver such small amounts of water, can trick us into thinking we are giving the trees more water than they are actually getting. Applying water for a longer period of time means that it penetrates deeply into the soil where tree roots are located.
As plants get bigger, their requirement for water increases but usually not their need for watering more often. We can compensate for this by increasing the number of emitters and the area under the tree where water is applied. This is done by adding more emitters under the canopy at greater distances from the trunk.
By doing this, the volume of soil that can contain water and the amount of water available to the trees increases. This usually means we can go longer between irrigations. If we just simply increase the number of minutes without adding more emitters, we run the risk of wasting water.
I generally discourage the use of drip emitters on trees that get more than 25 feet tall since so many are needed. These trees will do better in the long run on a different irrigation scheme, such as bubblers and basins.
Bubblers deliver gallons of water in minutes rather than hours. But the water must be contained in shallow basins surrounding the trees or it will go everywhere.
Changing over to bubblers from drip might be expensive. Before you go to this kind of expense, you can tell if this is needed by watering the trees with a hose once a week for a few months. If you see some improvement, this may answer your question. The only problem might be that many trees are getting ready for winter by now and you may not see much improvement until next year.
Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by e-mail at email@example.com.