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Aleppo pine blight damages trees grown in desert

Q: All the large pines on my property have branches that are turning brown in some form or another.

A: I have not mentioned this problem in my column or on my blog per se, so I’m glad you asked. I do have a post on my blog that talks about the branches of pine trees dying back and possible causes.

If the tree is Aleppo pine, the browning of the needles occurred during the winter, and these brown branches remain supple or flexible when you bend them, it is most likely a disease called Aleppo pine blight. This disease occasionally attacks other pine trees but is more common on Aleppo pine growing in the hot, dry desert.

Aleppo pine blight is not a true disease, as we think about diseases caused by some agent like a virus, bacterium or fungus, but is thought to be more closely related to the tree’s reaction to stress. The exact cause is not known but believed to be related to a lack of water during the summer.

The tree reacts with branches and needles turning brown in December. The branches look dead but bending them reveals they are frequently still flexible and alive. In extreme cases, these branches may die. This is common in Aleppo pine throughout the valley during the winter.

What to do? Certainly, we don’t want to spray chemicals because it’s not necessary. New growth appears from the brown but still supple branches in the spring. If some of the branches have died, new growth will appear somewhere beneath the dead parts.

Aleppo pine trees can be quite large. Their demand for water is high when they get this size. Their demand for water is not as high as mulberry, for instance, but their need for water is high because they are large trees. Because of their need for strong anchorage in the soil, applied water to the soil should be deep and at least half way to the ends of the branches.

Their demand for water will be about 400 percent more in the summer months versus winter months. This means, apply the same amount of water each time you water, but increase the frequency of these applications from winter to summer.

Q: I have a variety of succulents and cactus plants growing in pots on my balcony. They get sun in the morning until early afternoon. How should I keep their soil? Moist or dry?

A: I’m afraid there isn’t one easy way to water everything when it comes to cacti and succulents. Even though they appear somewhat similar, succulents are watered differently from most cacti. Even among cacti, there are differences in how they should be watered.

Adjust your watering to the needs of the plants. You will know these needs by observing them carefully. Let me tell you how.

All cacti are succulents but not all succulents are cacti. Cacti are in a subgroup of succulents more tolerant of dry soils. However, both cacti and succulents tell us when they need water through observation. Once you get in the habit of observing your plants, watering will become a breeze.

Both succulents and cacti push new growth after water is applied. Succulents have adaptations allowing them to store water during times when water is not present. If water is not present, they don’t grow much. When water is present, they use that water for growth until it runs out.

Using this information to your advantage, if you want a cactus or succulent to grow more, water it more often. If you want a succulent to not grow as much, water less often. But avoid watering too frequently. This can kill it.

Avoid a watering schedule but, instead, look at the plants. Remember, healthy plants can be 95 percent water. When they need water, leaves or stems begin shriveling or wrinkling as the internal water gets used up.

There is a misunderstanding about the word “overwater.” Overwatering occurs in two very different ways. First is watering too frequently. An example is daily watering. This type of overwatering is more likely to kill plants. Use restraint when deciding when to water again.

The second way to overwater is giving the plant too much water in a single application. An example might be watering weekly. This type of overwatering wastes water but is far less likely to kill plants. Make sure an irrigation is followed by an extended rest period without water.

Both cacti and succulents need a rest or dry spell between irrigations. The length of this dry spell varies among cacti and succulents. The only way to know this is through experience watering.

Use container soils that allow water to drain freely from around the roots. Use containers that have holes in their bottoms so water drains easily from the soil.

After watering, about 20 percent of the applied water should drain from the bottom of the container. Water draining from these containers helps remove salts that might otherwise build to damaging levels in the soil.

Get a feel for when to water individual plants through observation and avoid a watering schedule that treats them all the same.

Q: I keep my landscape cacti and succulents on the dry side. But I am uncertain how much water these plants use when kept outside in small- to medium-sized pots. They don’t have a large volume of soil to contain their water supply.

A: You are right. Cacti are watered less often when planted in the ground. They have a much larger root system compared to those growing in containers. Landscape cacti and succulents draw upon water their roots find in the surrounding soil. Potted plants are restricted to the water found only in their container.

Surprisingly, cacti and succulents of the same size kept outside in containers use about the same amount of water as those growing in the ground. But potted plants are watered more often but given less water during each irrigation.

Water cacti and succulents more often in pots and containers. How often depends on the cactus and the soil.

Cacti and succulents growing in the wild may have roots stretching distances eight to 10 times their height. These large, extensive roots are important for their survival.

When it rains, shallow roots slurp up the water quickly and put it into internal storage. After a rain, trunks, stems and fleshy leaves visibly swell with this stored water. They look plump. They react the same way after an irrigation.

Observe your plants to determine when to water next. To push growth, water more often. Water Opuntia or prickly pear cactus every three weeks during the summer to push new growth. Watering frequently can cause excessive top growth with shallow roots. Eventually, they fall over because they are top-heavy. Watering more often than this can kill it.

Always allow the soil to dry between irrigations. Look at the cactus. If it is starting to shrivel, then it’s time to water. If the container is getting light in weight, it is time to water.

Use a pencil. It is harder to push a pencil into dry soil than wet soil. Use a moisture meter. The meter should read “dry” when it’s time to water again.

Avoid glazed containers that are too small for a large cacti or succulents. Many cacti experts recommend porous, clay pots with drainage holes at the bottom. The width of the containers should be about half of the plant’s height.

Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.

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