Never too late To Prune Lantana

Q. I put off pruning my lantana. They bloomed until about a two weeks ago. Now, they are starting to cycle through the dying and rebuilding process. Can I prune them back now, the normal way, and still have good growth?

A. So, I take it, you did not prune your lantana this winter because it did not freeze. Or you just forgot. Now you are wondering if it’s too late to prune. No, it’s not too late. Do it now even though it’s starting to grow again.

            Lantana is what we call an herbaceous perennial in our climate. Winter temperatures are usually cold enough that the top freezes to the ground each winter. Spring pruning removes the top, close to the ground, and it regrows again from its base or crown. This winter it did not get cold enough.

            You know it has the potential to grow from its base. Cut it back hard to within 1 inch of the soil surface and it will “sucker” below these cuts. Give it some fertilizer and water after you make the pruning cuts.

Tangerine Leaves Curling

Q. Please help me to recover my tangerine tree leaves curling inwards. Most have very small black spots on them. l observed the leaves and don`t see any insects. l do deep hose watering during hot summer days.

Picture of tangerine leaves curling and dropping

A. There are lots of reasons for citrus leaves curling. This problem is near legendary for citrus leaves but the reason is usually environmental and not from insects or disease. I’m not saying it can’t happen but it’s less likely.

Citrus troubleshooting guide Arizona

Cold weather

            Since this question was sent to me at the end of winter, cold weather comes to mind. Cold temperatures can cause leaves to roll. Some say cold weather can cause leaf spotting as well. If leaf rolling was during the summer, guess what? High temperatures can also cause citrus leaves to roll.

Watering

            Moisture stress can cause leaf roll and leaf drop. When timing irrigations, make sure the soil is no longer wet when the irrigation water is applied. In the same token, make sure the soil does not get too dry between irrigations. Dry and wet soils can cause leaf rolling.

            What’s more important, in my opinion, is overall tree health. Plants in poor health are more susceptible to problems than those that are healthy.

Soil problems

            In the picture you sent, I noticed the condition of the soil surrounding these trees. The soil looked pretty bad, even by Las Vegas standards. Poor soil conditions leads to poor plant health in the future.

            Good soil health begins at the time of planting. I realize your tree has already been planted but soil improvement surrounding the roots at the time of planting is a huge future investment in plant health for years to come. In the future, excavate the planting hole 3 to 4 feet in diameter and 18 inches deep at the center. Mix good compost with your excavated soil at a rate of about 1:1; for every shovelful of soil, mix one shovelful of compost.

What to do?

            What can you do now? Put a half bag of compost on the soil surrounding the tree. On top of this, put a 4 to 6 inch layer of woodchips and water it in. Woodchips, where irrigation water is present, improves the soil health where most of the feeder roots of your tree are living.

Spreading good quality compost at the base of trees for its fertilizer content

            Improving the soil improves water, fertilizer and nutrient uptake by these roots which in turn improves the overall health of the tree. Soil improvement using this method helps remove some irrigation problems that could be causing leaf rolling. Overall, this means fewer problems for your citrus in the future.

Community mulch pile at the University Orchard North Las Vegas

            Get these woodchips free by visiting Cooperative Extension locations south of the airport or in North Las Vegas at the University Orchard in the Aliante community. For more information about these free woodchips call the extension hotline at 702 – 257 – 5555.

Compost’s Role in Landscapes

            Using composts as soil amendments in vegetable gardens has been a no-brainer in the past. We knew it contributed to soil organic matter content. Most vegetables benefited from high levels of soil organic matter so we had no problem adding it to vegetable beds.

How much organic matter is enough?

            We were taught in school that productive agricultural soils generally contain from 2 to 5% organic matter; some required more than others depending on what was grown. In soils with adequate amounts of organic matter, additions were not needed. But that concept of “one size fits all” when it comes to organic amendments is being challenged and the challengers are winning.

We have been educated that the ideal soil has 5% organic matter in it. But is that really enough for all plants?

            
We were told by scientists that landscape plants would not benefit from the addition of organic matter and that amending the soil at the time of planting was not necessary. Those of us working in arid and desert soils of the West and Southwest quietly challenged that generality and continued to add organic matter like composts to our landscape soils. We could see the benefit.

What is a "healthy soil"?

            Research during the past 20 years has challenged some of our previous thinking.  In many of our soils, regular additions of organic matter and its decomposition to humus is a necessary step in maintaining a vibrant and “healthy” soil and productive plants. Terms like soil health, soil food webs and soil ecology have become mainstream now.

We have always been told that a healthy and vibrant soil contains lots of worms. But does their presence really indicate that's all that's needed?

            Composting is the process used to convert organic matter into humus and employs many of the same microorganisms that perform the same function in soil. The concepts are very similar. The major difference is that composting provides a greater degree of control over organic matter breakdown than if it were left to an unregulated soil environment.

            Fungal and bacterial colonies, earthworms and soil inhabiting insects feed on organic matter. Microbial slimes and gums are produced when organic matter is converted to humus. These byproducts of composting and organic matter breakdown help cement soil particles together.

Most mushrooms are "saprophytic" which means they "feed" off of dead things, not living things. The presence of mushrooms in a soil is one sign that something in the soil is decomposing or breaking down. This decomposition is important for recycling, building organic matter and renewing life in the soil.

            This altered soil structure is filled with voids that permit the entry, percolation and exchange of water and gases. Improved soil structure or “tilth” is a major benefit from the breakdown of organic matter or the addition of compost.

            Byproducts from the decomposition of organic matter and the feeding by soil organisms improve the soil further by altering the soil chemistry and providing organic compounds that stabilize nutrients and assist in chemical reactions necessary for plant survival.

Some companies capitalize on the idea that compost adds "life" to soils like this ad campaign by Viragrow, Inc.

            When organic matter declines, humus levels decline as well. “Soil health” declines and with it landscape plants suffer. The rate of decline depends on many things including the type of soil, climate, management, nature of the organic matter and other factors.

Renewing soil organic matter with compost

            If deteriorating soil health is not caught soon enough, large volumes of quality soil organic amendments, such as compost, are needed in a process called soil remediation to bring the soil “back from the dead”.

Compost additions to soil improve it by adding aeration, improving water retention while also improving drainage at the same time, and rebuilding life in the soil.

            With these additions we see the improvement in soil health reflected in our landscape plants; more vigorous and healthier growth, more tolerance to environmental extremes, small amounts of fertilizer achieve greater results, less water is needed and plants experience fewer pest problems.

Managing soil health

            As managers of plants we must also manage our soils. The percentage of organic matter in a soil, and thus its humus content, is terribly important. Most soil test results provide the soil organic matter content.

            But, is knowing the organic content of our soils enough? To know how much and when to put it back, it is best to know how fast it disappears. Knowing the rate of organic matter decomposition is a powerful management and budgeting tool. With this type of knowledge we understand how often and how much compost to budget for to maintain soil and plant health.

             Similar to the composting process, the most powerful external factors controlling the conversion of soil organic matter into humus and its eventual disappearance are moisture and temperature. If soils are kept moist, accumulated soil temperature is the driving force in the loss of soil organic matter. At higher temperatures, soils decompose organic matter faster than in cooler soils. Hot, moist soils need additions of organic matter more often than cool, moist soils.

Compost used as a fertilizer

            Organic matter releases the nutrients it contains for plant uptake only when it decomposes. By decomposing, plants benefit as well as the macro and microorganisms that live in the soil. Decomposing organic matter also helps support beneficial soil bacteria, fungi and earthworm populations. The decomposition process of organic matter contributes to the breakdown of soil minerals which in turn further release the native plant nutrients they contain.

There are enough nutrients in compost that it can act like a fertilizer. Composts very in their nutrient content so it is difficult to claim them as a fertilizer. Some contain more nutrients than others. It depends on the components used in making the compost.

            In ways not well understood yet by scientists, the addition of composts to soils and plants and their breakdown impact plant health for the better. These impacts can be direct or indirect. Soils deficient in adequate levels of soil organic matter contribute to plant health by improving plant vigor, nutrient availability and uptake. This in turn improves plant tolerance to environmental stresses such as heat, drought, disease, mechanical damage and insect pests.

Composts role in fighting plant disease

            There are now dozens of reports on the suppression of some very common diseases in many horticultural crops through applications of composts and compost teas. Numerous studies in greenhouses have demonstrated the suppression of common plant diseases found or transmitted in moist soils such as damping-off, root rots and vascular wilts. Disease suppression has also been demonstrated on field crops.

Are available for making compost tea. They are very similar to making any kind of tea; the compost is put inside of a "teabag" and this compost is allowed to "steep" in the water. Of course good quality water is used. This compost tea can be sprayed on the leaves of plants where it can act like a fertilizer and suppresses some foliar diseases. This compost tea is perishable so it must be used relatively soon.

            Composts and products formulated from humus have been used by landscape and turfgrass professionals for 70 years.  However, with the advent of inexpensive nutrient rich chemical and synthetic fertilizers 60 years ago the use of organics such as manures and composts as fertilizers has nearly disappeared. It could be argued that with this disappearance we saw a general increase in disease incidence and the pronounced use of pesticides to control these diseases.

Compost used to "topdress" lawns

            More recent research has demonstrated the potential for using sources of organic matter such as composts and organic topdressings in the management of high quality turfgrass.  Several turfgrass diseases such as Fusarium patch, red thread, damping off, brown patch, dollar spot and snow mold have been suppressed by topdressings of compost.

           It has been further demonstrated that these suppressive effects were generally from the biological activity of the organic amendments, not just because of improvements in the chemical and physical properties of the soil. The disease suppressive effects of organic amendments generally increased with increasing rates of application and were not as pronounced when sterile compost was used.

All composts are not the same 

Choice of feedstocks and how compost is managed impacts compost quality. This in turn is reflected in landscape response. Producing humus from organic matter takes valuable time and resources. Composts must be monitored and submitted to test for nutrient content and biological activity. Selecting the appropriate compost is critical in achieving soil improvement and improving plant health.

Smelly Potting Soil in Oven Disputed

Q. Earlier in March you talked about fungus gnat problems in potting soils. You recommended baking the potting soil in the oven. But I’ve heard this stinks up the whole house! I might try it in a gas grill outside, but not inside.

Potting soils are lightweight soil mixes that usually contain peat moss and perlite as part of the soil component to minimize weight and maximize porosity.

A. I used to think the same thing about baking potting soil in the oven. The common response by gardeners is not to do it for that very reason; it stinks up everything! But we tested it recently and it worked just fine as long as the temperature of the oven was below 180F. I think the smell problem occurs when the temperature of the oven is set too high.

            I prefer “solarizing” potting soil in sealed, clear plastic bags for a couple of days to kill fungus gnats. The temperature of the soil does not have to be as high as it does to kill everything in the soil, a.k.a soil sterilization. If the temperature of the potting soil reaches 140 – 150 F for 30 minutes, through and through, it’s enough to kill insects.

            To sterilize potting soil, completely ridding it of all insects as well as harmful microorganisms, the temperature must reach 180° F for 30 minutes throughout the soil. Attaining this temperature by solarizing is doable if there is plenty of sunshine, the soil is moistened, placed in a clear plastic bag and left in the sun long enough.

            To be on the safe side, I solarize the soil with one side facing the sun the first day. Then I turn the bag over and solarize the other side on the second day. I check the temperature with a temperature probe through the plastic bag to make sure the temperature was high enough.

            I would not recommend putting potting soil in a gas grill and firing the temperature up high. Low temperatures in gas grills are harder to control. Excessively high temperatures will “burn up” the organics in the potting soil. That’s when it gets stinky.

            This cool, overcast spring presented some real problems. Cool temperatures and overcast skies did not allow solarization to reach the temperatures needed inside the bag. I enlisted the aid of a brave volunteer with an oven that had accurate temperature controls. She placed a half bag of potting soil on cookie sheets and into a domestic oven.

            The lowest thermostat setting for the oven was 160° F. The temperature inside the oven stayed around this temperature for 30 minutes and the soil allowed to cool inside of it. Voilà. No fungus gnats and no off smell.

Western Redbud Better Choice but Harder to Find

Q. I can never find Cercis occidentalis, Western Redbud, at local nurseries. Any idea where I can locate it?

Western Redbud after flowering

A. Thanks for giving me the Latin name for this tree instead of just Western Redbud because that eliminates all confusion about which tree you might mean. If you like a reddish pink splash of spring color in about March on a small tree, you will like this tree when it flowers. The Redbud most people buy is an Eastern Redbud but it is not as suitable for our climate and soils as its Western cousin or even the Mexican Redbud.

Mexican Redbud

            Eastern Redbud is the tree that people call “Redbud” from the East Coast to the West Coast. Western Redbud is unique. It has never gained the same popularity. This is the same tree that polkadots the Grand Canyon with rosy plum color every spring.

Eastern Redbud has some soil issues in the West and not as adaptable as Western Redbud

            But Western Redbud has significant advantages over the Eastern Redbud in our climate and soils. First off, Western Redbud handles the chemistry of our soils much better than Eastern Redbud. That’s because it evolved here. It is native to southern Nevada and specifically the Charleston Mountain Range of Southern Nevada. It is small, seldom reaching heights over 20 feet tall, the perfect size for a single-story home and smaller patio-sized landscapes.

            However, it will not tolerate having “wet feet”. In other words, don’t water it too often. Give it a lot of water when you do water it and then hold off and let the soil dry before you water it again. It is native to the foothills of dry Southwestern areas including Utah, Arizona and California. It’s one of our desert natives.

            I also think the Western Redbud is a prettier tree when it’s flowering than the plain old Redbud.

            Try our State Forest Nursery located in the north part of the Las Vegas Valley. They specialize in local native plants. 702-486-5411.

When to Fertilize Lawns

Q. When is it time to start fertilizing lawns again?

Lawns can be beautiful but they need regular feeding. The light green color of this lawn is an indicator it needs an application of nitrogen fertilizer. That nitrogen fertilizer will turn that light green lawn into a dark green lawn in a matter of a couple days.

A. It depends on whether the lawn is fescue, only Bermudagrass or Bermudagrass overseeded in Fall to maintain green winter color. Fescue lawns and overseeded Bermudagrass lawns are fertilized the same during winter months.

Ammonium sulfate fertilizer contains only nitrogen that the plants need when their color is not dark enough. The sulfur in the sulfate is also important for plants but in the case of light green color, all that's lacking is nitrogen.3 to 5 pounds of this fertilizer spread evenly over 1000 ft.² of lawn and watered in will turn the color a deep green instead of light green.

            Fescue and overseeded Bermudagrass should have been fertilized last Thanksgiving to maintain dark green color through winter. If this fertilizer application was missed and temperatures get cold, the lawn can turn brown when it gets very cold or just light green if it does not.

            The next fertilizer application to fescue lawns would be when air temperatures enter the 60s. Fertilize Bermudagrass that was not overseeded when temperatures enter the 80s.

Once or twice a year add a better quality fertilizer to the lawn like this one. It has a little bit of phosphorus, the middle number. Lawns don't need a lot of phosphorus because we don't grow them for their flowers and fruit. I would like to see the potassium, the last number, higher than this but this is a good lawn fertilizer.

            Established lawns require fertilizers containing high nitrogen, and occasionally an application of iron, for dark green color. However, they will perform best if this fertilizer contains also low levels of phosphorus and moderate to high levels of potassium.

            For this reason, fertilizers similar to 21-7-14 or 10-5-10 are frequently recommended for lawns. Some people use only high nitrogen fertilizer such as 21-0-0 and omit phosphorus and potassium.

            I think this is a mistake and a good lawn fertilizer should be applied at least once during the growing season. Instead, experiment and try fertilizing with only half the amount of fertilizer recommended on the bag. This is all that is usually needed if you are not bagging lawn clippings but mulching them back into the lawn using the mower.

Digging Holes to Plant Fruit Trees

Q. How big do you dig your holes for fruit trees?

This was a hole dug for a bare root fruit tree about 1 inch in diameter. The whole is about 3 feet wide and not much deeper than needed for the roots. The soil taken from the whole was mixed about 50-50 with compost and used for planting around the tree roots. Water was added to the hole at the same time the soil was put around the roots. The trees were staked to prevent the roots from moving.

A. I generally like to dig holes for fruit trees in five or 15 gallon containers about 3 feet wide and just deep enough for the root ball from the container. But the size of the hole depends on the condition of the soil for planting.

            If the soil is a very poor soil, I make the hole wider but not any deeper unless the soil does not drain water in several hours after filling it. These situations are rare. I don’t like deep holes for plants because of soil settling issues and causing plant problems later.

Finished planting fruit trees at the Ahern Orchard in Las Vegas. Berms or doughnuts were created around each of the trees so they could be watered as soon as they were planted. They were watered three or four times immediately after planting to remove air pockets and sell the soil around the roots.

            Our desert soils can be unusually hard but in some parts of the Las Vegas Valley there are “caliche layers” that are as hard as cement and require a jackhammer to break through them. If you or your neighbors have a pool and this layer was not found when it was put in, then you don’t have a caliche problem.

            The soil removed from the hole should be mixed with compost before planting. Use a mixture one part compost to one part soil. Another option is to use an “imported” soil mix for planting.

            If the compost used in the soil mix is “rich”, no fertilizer is needed for the first year after planting. If the compost is not rich, then add a starter fertilizer high in phosphorus to the soil mixture before planting. Rich compost is usually made with some sort of animal manure.

            Plant the tree the same depth as it was in the container making sure that the roots are covered with no more than 1 inch of soil.

            As this soil mixture is added to the hole, add water to the hole at the same time you add the soil/compost/fertilizer mixture. This slurry of water and soil mixture removes air pockets and results in a tree held solidly in the soil after planting. Small trees will not require staking if done right.

            Surround the plants with a donut and fill this donut with water several times during the next week before you turn it over to the irrigation system.