Pruning Boxwood and Rosemary Hedge Can Result in Disaster

Q. I have a neighbor concerned about his rosemary and boxwood hedges. He has been having trouble with the foliage browning and falling off. His landscapers recommend he cut them to the ground but he opted to cut them back by half instead and let them regrow. Can you tell me a little about these and your opinion about how to properly care for and what he should do to get them looking their best again?

boxwood

A. When rosemary and boxwood, or any plants for that matter, are continuously pruned with a hedge shears it causes them to get thick and bushy at the point where they are continuously sheared. This increases their density on the outer edges of the plants.

            Shearing causes the interior of the hedge to become very dark. This darkness cannot support leaf or new stem growth. The older stems on the inside of the hedge drop their leaves.

            All the new growth occurs only where it is sheared. Perhaps only an inch or two of the outer surface of hedged plants have leaves. The dark interior is leafless.

            If we cut too far back into the hedge we expose the older wood that has no leaves. The wood is alive, but without leaves. Once this interior wood begins to receive sunlight again, new growth will usually occur on the older wood.

            The rate of recovery of this older wood depends on the plant. Rosemary will come back faster than boxwood.

rosemary

            He will start to see growth coming from older wood exposed to sunlight as suckers. In technical terms we call this adventitious growth. Boxwood will do the same thing but it is much slower to react and fill in.

            If he is patient he will see new growth slowly fill in the canopy.

            If he had cut it back close to the soil surface, the same thing will occur on the Rosemary but it will be slow to grow back into a hedge. Boxwood will even be slower.

            In cases like these most people do not want to look at a hedge trying to fill back in and would elect to replace these plants.

            Once plants are cut with hedge shears for a couple of seasons they are very difficult to reestablish again as plants that are no longer a hedge. The interior of the hedge is just too woody.

Lawn Care During the Heat

Watering your lawn improperly during the summer heat could contribute to disease problems in fescue. Tall fescue lawns make present fewer problems than other grasses in the hot desert climates. They are grass which is cool season, preferring cooler times of the year or cooler climates, but can normally handle the heat fairly well. As long as the heat is dry.

Summer patch

When we grow fescues in the humid climates and apply heat to them, they frequently succumb to diseases. As our summer monsoon season approaches, it is wise to remember that how you irrigate and manage your lawn may determine if your lawn gets diseases or not.

Follow these management practices if you are not already:

1.      Irrigate during early morning hours so the lawn does not stay wet during the night.

2.      Water deeply. Tall fescue can be a deep rooted grass. Deep rooted grasses typically have higher drought resistance than shallow rooted grasses.

3.      Do not let your lawn become water stressed. Stressing lawn grasses predisposes them to diseases.

4.      Aerate lawns prior to summer heat or in the fall to encourage deeper rooting which helps drought tolerance.

5.      Applying fertilizers regularly. Lawns require fertilizers all year long including the summer months. Apply fertilizers in half rates during the heat and water them in thoroughly after the application.

6.      Apply fungicides to the lawn at the first sign of disease. Fungicides primarily protect plants from diseases. Seldom do they cure diseases once they are full-blown.

7.      In future years try organic fertilizers such as compost or vermicompost as alternatives to traditional granular fertilizers. Regular applications of compost materials tend to reduce turfgrass diseases.

Leaf Yellowing on Locust Possible Sunburn and Borers

Q. Do you have idea why some many of the leaves on my locust tree are turning yellow?

A. The most frequent problem with locust trees, Idaho or black locust, is borers in the trunks. This will cause exactly what you're talking about, yellowing of leaves and leaf drop.

            This is followed by branch dieback. Dieback of limbs may take a couple of seasons after the initial borer attack but if you are not looking for borer damage early, you will see leaf drop a couple of years into the attack.

            Borers entered the trees usually where the tre is sunburned. This is normally on the west and south facing sides of the trunk or limbs. Horizontal limbs may be damaged on the upper surfaces as well.

            Check the bark on the trunk or limbs see if it is loose. It may easily pull away from the trunk particularly on the south and west sides. Damage is usually on larger diameter parts of the tree.

            Remove bark away from damage to areas and clean the damage down to fresh wood. You don't need to paint it but if you want it painted, paint it.

            Use a liquid insecticide soil drench to help protect the tree and give it a chance to recover during early stages of an attack.

Kiwis Possible But Consider Winter Low Temperatures

Q. Is it possible to grow kiwi in Las Vegas? I love the flowers and big leaves on the vine and am not looking for a big harvest.

A. Kiwi requires a growing season of at least 220 days which we have and that is one thing in our favor. What works against it are our low winter temperatures, strong sun, low humidity, strong winds and desert soils.

immature kiwi

            You can do it but you need put it in a warm winter microclimate somewhere in your landscape. Once Kiwi gets established, it can handle lower winter temperatures. Protecting it from freezing temperatures when it is young will be very important.

            It does not like windy locations either. Wind deflectors or wind barriers will help as well.

            Kiwi does not like our alkaline desert soils or soils with a lot of salt. Soil improvement and good drainages is a must.

            Kiwi can handle hot, arid conditions up to about 115° F. without too much difficulty. This will run a bit contrary to what you might read in the literature.

            So if you are going to make this work you will need a male and female plant. The variety Hayward is commonly used commercially for fruit production. It is grown in the Central Valley of California which can get pretty warm.

            The male variety, Chico, is commonly used as a pollinator. Just make sure whichever Kiwi female you select a male that blooms at the same time as the female.

Prepare the soil thoroughly with amendments and leach the soil with lots of water before planting to remove the salts. Make sure the soil drains easily so you might want to plant in a raised bed. Plant in a location that gets morning and early afternoon sun but is protected from late afternoon sun.

Kiwi is a vine so you will need to construct some sort of trellis to support it. This is a plant that will not tolerate dry soils so make sure the soil is kept moist during the summer months. I would use a 3 to 4 inch layer of wood mulch on the surface. This will help Kiwi a lot.

            Another option but not as much fun it is to grow hardy Kiwi. It will handle much lower temperatures. It has much smaller fruit but many people say the fruit is much better tasting than commercial Kiwi.

Petunias Not Producing Flowers

Q. My husband planted some gorgeous petunias in early April.  At first they were all blooming and the planters were beautiful but now there isn't a single flower in either planters.  We noticed a tiny black insect on the plants and there were many holes in the leaves so my husband sprayed them with Sevin thinking that would do the trick.  All we have is two planters filled with very healthy green plants but no flowers. 

A. This is most likely tobacco budworm. I have attached a fact sheet on the pest. Tobacco budworm larva or worm puts holes in leaves and eats flower and leaf buds. The black drops you are seeing is probably budworm "poop" from eating the plant.

            Spray the plants with a synthetic pyrethroid insecticide, Bt or Spinosad. Sevin will probably work but the problem with Sevin is that it is deadly to bees and when plants are in flower, bees are normally attracted to them. Spray plants in the evening or very early morning hours when bees are not active.

My Tomatoes Not Developing Good Red Color

Interveinal (between the veins) chlorosis (yellowing)

In desert regions, we sometimes notice that plants growing under higher temperatures develop yellowing of the leaves when exposed to intense sunlight for long periods of time. This yellowing does not appear to be associated with a lack of any particular type of nutrient such as iron or manganese, a common problem in desert soils. We don't see the typical micronutrient deficiency symptoms such as interveinal chlorosis; yellowing between the veins while the veins remain green. I have talked about this in previous postings, probably relating to intense sunlight. Usually, growing tomatoes under light shading (no more than 30%) during times of intense sunlight helps to alleviate this problem.

Retired vegetable specialist from the University of California, Hunter Johnson, explains it much better. He is talking to green house growers but the message is the same. Reduce intense sunlight on tomatoes for better color development. I borrowed this posting from a University of California publication several years ago. http://vric.ucdavis.edu/pdf/TOMATO/tomatoes_HomeGarden.pdf

Solar Yellowing in Tomatoes

Yellow discoloration invariably occurs beginning in the late spring months under greenhouse conditions, or from that period on through the summer in the open field in inland areas where daytime temperatures regularly exceed 85^OF. An accurate term for this condition is “solar yellowing" because the source of the problem is the sun. It isn't only the heat of the sun or the temperature increase in the

Tomatoes not developing good red color in heat

fruit that creates the problem, but also high light intensity. This was shown by Dr. Werner Upton, who coined the term "solar yellowing" in research he conducted on the subject in 1970. His treatments involved shading or painting the fruit either black or white. Black-painted fruit were higher in temperature than exposed fruit, but discoloration was highest in the exposed fruit. His conclusion was that short-wave radiation was largely responsible for defective coloration.

The reason for the yellow or yellow-orange color, rather than the normal red, is that the red pigment (lycopene) fails to form above 30OC (86^OF). This phenomenon was first described by researchers in 1952 and was later confirmed by others. When lycopene fails to form, only carotenes remain for fruit color. In the field, some red color forms when day temperatures rise above 85^OF because of fluctuation in noninhibiting temperatures during other parts of the day or night. An orangey-red color results. 

In production areas where temperatures do not exceed 85^OF, much higher red color develops.

For good uniform red color to develop, high temperatures should be avoided and fruit should be protected from short-wave radiation in high light intensity areas. 

Dr. Upton showed that sprays of non-phytotoxic whitewash will help. In greenhouses, growers who intend to mature fruit in May and June should begin to alter their pruning practices in March by allowing two leaves to develop on axillary branches instead of the standard practice of removing these branches.

The author is Hunter Johnson, Jr., retired University of California Cooperative Extension Vegetable Specialist, Riverside Campus.

Bees Drowning in Swimming Pool

Honeybee visiting peach flower

Q. My daughter has an above-ground swimming pool and she is encountering a lot of bees floating on her pool water. First she is not happy to see them die. Second she is not happy for them to be there as her son and daughters swim in the pool and they don't want to get stung. Can you make any suggestions?

A. The bees are looking for water to take back to their hives. When it is hot out, bees are continuously hauling water back to the hives to keep it cool. And consequently they drown because the pool is not shallow.

            She can try putting out a shallow depression in the landscape away from the pool and see if they will land there instead. They would prefer to haul water from a place that has a very shallow amount of water like the edge of a pond or stream.

            This way they can land on solid ground, take water and fly away. Once they find it, they may make lots of trips to it for water and be regular visitors. There is a hive somewhere fairly close by.