If bermudagrass flowers like this one are left to release pollen in the air, they will cause “hay fever”. That’s why common bermudagrass is not permitted for planting in Clark County, Nevada. Pollen Alert That’s what we see on our advisories in the early spring regarding pollen from mulberry, ash and junipers. The pollen alert continues through the “pollen season” as we go from mulberry to pine to olive. Pollen season might last until May. Right now we’re in “mulberry season”. Some pollen like mulberry is light enough and can be pushed by the wind and carried by pollinators like honeybees. This type of pollen causes “hay fever” while others are considered “sticky” or “heavy”, too large to travel long distances in the air and not considered allergenic. Male flowers from the ‘Bonita’ ash tree. Because this ash tree is male, it produces only male flowers. Great for producing no seed but not if you dont want pollen. Hay Fever             “Hay fever” was a misnomer from the start. It was an old historic association with the cutting of hay in the spring and not paired with flowering of plants that cause the release of pollen. Back then pollination by plants was not studied much. Tree and shrub pollen was not considered responsible for “hayfever”. Most allergenic pollen comes from uncontrolled, wild grasses growing where rain was available. These allergies were caused by pollen floating in the air but the idea of “pollen fever” never caught on. Until recently people with severe symptoms were told to move to the desert Southwest where “pollen fever” was never considered much of a problem. Maybe that was the case back then, but they are wrong now! Common bermudagrass flowering and it will seed next spreading pollen and seed everywhere. When bermudagrass escapes mowing, it creates pollen, allergies and seed. Desert and Hay Fever             As people moved to the desert Southwest and started planting more and more “desert trees” like Acacia, Mesquite and Palo Verde, “pollen fever” (aka, hayfever) developed into more of a problem. Typically, trees and shrubs with large showy flowers like oleander do not contribute much to the “hayfever problem”. This pollen is heavy or sticky and did not travel in the air far from the flower and the plants released pollen too large to cause “allergy problems”. Most of the “problem pollen” comes from “non-showy” flowers commonly found on olive, mulberry, pines, ash trees, mesquite and the like. Oleander flowers are quite “showy”. Showy flowers are not typically allergenic because the pollen is large and/or sticky. Planting Restrictions             Now we have planting restrictions in population dense Clark County that prohibit the planting of male mulberry trees or olive trees that produce lots of fruit. So, is it “illegal” to plant mulberry trees in Clark County? Yes and no. It is “illegal” to plant male mulberry trees but not the female trees. Mulberry flowers are called “catkins”. Flowers in mulberry are like ash trees; they are either male or female depending on the sex of the tree. How about olive trees? Yes and no, but for a different reason. Olive trees always have both male and female parts in the same flower so we focus on the so-called “fruitless mulberries” and hope that these trees reduce “hayfever” in large communities. Mulberries, similar to ash trees, are bought as either male trees or female trees. As I have always said, plant sex is much more interesting than animal sex because of its diversity. Olive trees are both male and female so their flowers, unlike mulberry and ash, contain both male and female parts. 

Q. Does pineapple guava need a pollinator plant to produce fruit? The edible flowers bloom in May and have the wonderful taste of cotton candy! Should I get my pineapple guava tree a boyfriend? Flowers of Pineapple Guava A. First, let’s talk terms. A pollinator is an insect that helps plants produce more fruit by transferring pollen from one plant to another. Examples of pollinators are honeybees. A pollenizer is the plant that supplies this pollen to another plant to help it produce more fruit. So, I think you are asking for a pollenizer plant for pineapple guava. A pollinator, honeybee, visiting a peach flower and it will encourage fruit set. Now let’s talk pineapple guava. If the flowers are pollinated properly by a pineapple guava that is not exactly the same as the mother plant (pollenizer), the flowers will produce fruit. Some plants may be even self-fruitful to a degree. The amount of fruit produced depends on the number of flowers it produces and closeness to a pollenizer plant. To make sure to get fruit from the flowers, give the plant a “boyfriend” (or girlfriend). The reason for this are because of its genetics. In technical terms, the flowers can be non-receptive to pollination by the same or similar plant (variety or cultivar) depending upon genetics. So to make sure you get fruit, plant two different varieties of a pineapple guava in close proximity, otherwise it might be a trickle of fruit at best. The flowers of pineapple guava are edible and the taste is not affected by a pollenizer. Pineapple Guava and the Desert Pineapple guava performs well in desert landscapes. They can handle our heat and they can handle our cold. They can even handle a lot of the rock mulch used in many landscapes. But they are “normal” water users (mesic) and not xeric like many of our native desert plants. Flowers of pineapple guava with the same genetics are “self infertile”… in other words as much as the honeybee visits these flowers they will not set fruit. Even if the honeybee visits other pineapple guava, if they are too similar genetically then they will not create fruit. But the flowers are still yummy! Pineapple guava is a good choice for our desert climate in landscapes, but they are not true “desert plants” so they grow better with a little bit of organics like compost mixed in the soil at planting time.

Q. I have a star jasmine that is very woody growing behind some front greenery. I heard you mention once not to prune “flowering wood”. What does that mean? Peach flower buds opening on peach “flowering wood”. Sometimes, as in the case of peaches, the flower buds are formed the previous year they bloom. Other times flower buds (as in the case of oleander and Texas sage) they are formed on the newest spring growth. This creates a slight delay in flowering after pruning in the spring and summer months. Texas sage (ranger) produces flowers on “current seasons wood” so if they are pruned when growing there is a pause in flowering until new growth has time to put on growth with flowers on it. A. It means pay attention to the time of season you’re pruning and its relationship to when the plant produces flowers.  Warning: we are talking about plants valued for their flowers, not fruit trees! Fruit trees are pruned at a different time because we value their fruit. The flowers are not as important to us in fruit trees.  If you remember one thing, remember this; the best time to prune any plant valued for its showy flowers, is as soon as possible after it finishes flowering. Enjoy the flowers, and then prune! Shrubs like oleander that need to put on some new growth to flower will not flower after severely cut back until it reaches close to its mature size, which in some cases can be quite large. If it’s in the spring, prune it for flowering after it finishes in late spring. If it flowers all during the growing season, then wait until fall or winter when it stops flowering. Avoid all dramatic or “heavy” pruning of nearly all plants during the summer heat.             Plants need time to produce flowers. Some plants also need the right time of year. If plants produce flowers all season long when growing, then wait to prune them until they finished their show by mid fall or early winter. Probably one of the best known examples of flowering at certain times (photoperiodic flowering) is poinsettia which must only get a certain number of hours to create “flowers”. Light for longer periods than this or shorter only produces green leaves. Star jasmine typically produces flowers after a flush of spring growth; not right away in the spring. The time of flowering for this plant is more similar to oleander or Texas sage. As long as they are old enough, they start flowering as soon as there is some growth. This tells you they need a little bit of growth to produce flowers. Plants that grow like this we say f”lowers on current season wood”. Can you see why oleander, Texas sage or star jasmine shouldn’t be pruned during the summer? Instead, they are best pruned during the winter when spring and summer growth provides the new “stem growth” needed for producing flowers. If these plants are pruned just before or after they start their new growth in the spring, it causes their flowering to “pause” until there is some new growth.

Q. I don’t like what I’m reading about Imidacloprid (frequently found in borer control insecticides) and wanted to know if there is a better insecticide that won’t harm bees. Bayers Tree and Shrub Insect Control insecticide is one of many insecticides approved by the USEPA for killing some borers, like Emerald Ash Borer (not currently found in Nevada).  A. You are talking about an ingredient (tiny letters on the label under active ingredients) found in several different products rather than an actual product name (big letters) found on the label. The actual or product name might be “Merit” for commercial applicators and “Bayer Tree and Shrub Spray” for homeowners but also many others Some Countries Banned It As a “class” of insecticides, the neonicotinoids are the most used group of manufactured insecticides in the world. Insecticides containing imidcloprid have been banned for use in some countries due to accumulated evidence. That particular ingredient is still approved for use in the United States but has faced a lot of environmental problems and may be eliminated in the future. It has been implicated in the death of some pollinators like honeybees when visiting the pollen contained in open flowers. How to Apply it Safely The label information for these types of products gives you a clue about how to apply it properly. If you must use this product, apply it to plants after they have finished flowering. This helps prevent the transmission of this ingredient to pollinators. Alternatives At this particular time I don’t know of any insecticide available or permitted for use that has the same potential for controlling borers as imidacloprid. Its major advantage is also, potentially, its disadvantage; it is a long-lived systemic insecticide that can potentially be harbored in flowers, fruit produced and plant parts for up to 12 months. The only other option I know that can work is the digging of these problem insects from infested trees as they are seen.   Borers can be removed from an infested limb with a sharp, sanitized knife.

Q. My backyard has several planting beds containing roses, rosemary, mock orange, euonymus, pyracantha, lantana, sago palms, and other plants. I added rock to the soil surface eight years ago and these plants started to decline in about five years. I decided to remove the rock and put woodchips down instead but afraid of roaches entering the house from the woodchips. Irrigation valve box amongst plants receiving water. When you combine woodchips, water and a valve box it is normal for cockroaches and spiders to live and enter there. Spray the inside of these boxes with an insecticide once a year to help reduce these numbers. But this will not stop them from helping to decompose the woodhips. A. Insects such as cockroaches like water and something to eat. They live in the woodchips exposed to water because they help break down debris from the wood chips. Cockroaches, unpleasant as they are, are decomposers. Their favorite place to congregate in the landscape is in irrigation boxes where it stays wet. They are attracted to these wet areas and warmth of your home when it gets cold so they may come inside as their populations get larger. Keep landscape areas close to the home dry. Apply water to landscape plants no closer than 3 feet from your house exterior walls. There isn’t a good reason to apply water closer than this. In a desert climate where there is limited rainfall, plant roots follow irrigation water. Irrigating foundation plants on the side away from the home causes their roots to grow in that direction. Keeping the soil dry surrounding your home also reduces water damage to the cement as well as reducing insect problems inside the home. After removing the rock and before you apply woodchips, sprinkle the wet areas around plants with a rich compost to help feed the plants, enrich the soil, and start the decomposition process.

Q. I am a young gardener (25) in Henderson, specifically Green Valley, near the Pittman Wash. I am interested in the cultivation of plants not only for their aesthetic value, but their benefit to wildlife as well. This has steered my interests to pedology and edaphology as well as horticulture and botany. From what I have gathered from the USDA soil survey of the Las Vegas Valley (published in 1985), my residence (and therefore garden) lies near a boundary between the ‘McCarran’ and ‘Jean-arizo’ soil series.  From direct observation, it seems I am situated more so in the McCarran series area. With massive soil in the lower C horizon, and sticky and plastic qualities throughout, how does this effect irrigation protocols and amendments types and amounts? The reason I ask is I recently purchased some premium compost from Viragrow (thanks for the rec), and want to make sure I use the correct ratio of compost to native soil to prevent reinforcing any drainage issues associated with clay soils. The bare, native soil I am about to cultivate drains moderately slowly (some areas 15 minutes, other areas up to an hour). The only plants that have ever been in there were some poorly pruned Texas Sage (Silver and Green Cloud varieties) which have been removed. This area was not irrigated for many years, with the plants subsisting on incidental precipitation and irrigation diffusion from neighbors’ lots. The irrigation to this area has been repaired, and a large ornamental and small productive garden is now planned to be planted there. Are there any good resources, preferably more up to date than 1985, that can provide more information on local soil series and how to mitigate the inhospitable qualities of such? A. You live in the Pittman area of Las Vegas and Henderson.  Description of the Pittman soil series in Las Vegas and Henderson, NV. Most native soils in that area are classified usually as “heavy” which means they have quite a bit of clay and smaller silt particles. Water drainage can be a problem in these soils if the soil is irrigated too often. For this reason, I tell people that if all the water in a hole on the property drains overnight, it’s okay. If this were Wisconsin or Iowa then it would be different. Those soils are beautiful compared to the Mojave Desert soils. The soils for subdivisions oftentimes are imported or man-made and may not represent the native soils in those areas. If you have in imported soil on your property, then it may not be representative of the soils map. I am very familiar with NRCS soils maps for Southern Nevada and Northern Arizona, and I know the McCarran soil series quite well. It represents a huge area. So, make sure you are actually dealing with the native soil and not one that’s imported. You should be able to see that from the soil horizons. But overnight drainage for landscape soil would be okay for most landscape plants. This may not be true of Mojave native plants. If you are growing Mojave natives then I would suggest either not using an irrigation controller or using it only to water manually and not leave it on a schedule. As far as more information is concerned, Dr. Dale Devitt (soil science researcher) and I are in the process of publishing a book that you might take a look at. It’s available on Amazon in digital form. If you want a hard copy or digital it is also available from the publisher. Dr. Devitt teaches in the biology department at UNLV. Dr. Devitt is a “hard” scientist and I consider myself a “soft” scientist who focuses mostly on transferring difficult information in terms more easily understood. Together we have published about 40 peer-reviewed scientific research articles in various journals.  Dr. Devitt is the local soils expert and knows more than anyone about soils and water movement and plant use in the Mojave Desert. But honestly the book takes much of this difficult information from an urban tree perspective and tries to simplify it as much as possible. It’s really rehashing a lot of the same information but puts it into one book. Any of the Cloud series of native plants (Green Cloud, Silver Cloud, etc.) will be sensitive to soils that drain poorly. Their roots will tend to die due to poor drainage. In soils like that, consider planting them on a hill or berm about a foot tall and perhaps about six feet wide. This will give the roots a chance to grow in a raised soil that will drain better.

Q. What plants can I plant in my front and backyards? I want plants that grow large enough to produce shade. No shade on this south facing wall of this home. Wow, its hot! Shade the walls of this house to reduce electricity use in the summer. If they are deciduous then the sun can warm this house with sunlight in the winter. Shade the walls and windows. That is all that is needed, Not the roof. A. Shade only what’s needed. This is usually the West and South windows and walls. A single-story home only needs, at the most, 25 foot-tall trees or shrubs. A two-story home can handle trees to about 35 or 40 feet tall maximum. Selecting trees taller than needed just looks “funny” when they are mature. Big trees need big spaces like parks and malls to look good. Select Trees by Low Temperature Winter low temperatures should be the deciding factor for permanent trees and shrubs important to the design of the landscape. There are plants used for “fun”. Fun plants can be selected for any low winter temperature. But expect damage or lose them during cold winters. In the Las Vegas Valley, use a winter temperature around 20°F minimum for the most important trees and shrubs in a landscape.                To see which plants are available. There are three choices; buying from a local nursery or garden center, taking a road trip to buy plants, or purchasing plants online. Buying online starts around October with shipments beginning in January for spring planting of winter hardy plants. Plants bought online won’t have any soil around the roots so more care at planting time is needed.             To aid your search for the right plant, use two places online; the plant database from the Southern Nevada water Authority or Arizona State University’s (ASU) plant database by Dr. Chris Martin. To access ASU’s plant database, type in the plants “common name” followed by “ASU”. To access Southern Nevada Water Authority’s database, start by typing in “SNWA” and “searchable database”. Pick 3 to 5 different plants in the case the plant you want is not available.

Q. If anything, what can the different species of weeds tell someone about the soil conditions they’re found in. For example, do dandelions only grow in certain pH ranges or does puncturevine thrive only in certain sodic concentrations etc. etc.? I want to understand the most about my land via the plants that grow on it unassisted. I apologize for the lousy picture. I took it from a slide I had made a long time ago. This is Lake Mead and showing the change in native plants (weeds) that occur with a change in soil moisture. Plants are very different closer to the Lake than further away due to less available soil moisture. As soil moisture changes, the plant communities change as well as their numbers (density) and sometimes even their height depending on the plants. A. Which weeds are growing on native soil or disturb soils can tell you a lot. It can give hints about the chemistry of the soil and it will tell you a lot about its structure, if the soil has been disturbed or not, suitability for different plants and availability of water.  I look at the type of weeds growing, the number of weeds and how tall they are. Wherever there is subsurface water there are a lot more plants per square meter and they are usually taller. Native soils high in phosphorus tend to favor those plants that flower more and produce seed. Crappy local native soils don’t grow much of anything.  Dandelions for instance like disturbed soils, high phosphorus soils and they are very good at competition that’s one reason they can survive in lawns while common Bermudagrass does not. How the local plant community and the soil is managed influences which weeds grow. There are plants such as salt cedar which does favor growing in soils high in salinity but I’ve not seen a reference to sodic soils. That could be a question you could pose to Dr. Devitt.  Some research questions I wanted to ask include different amounts of irrigation applied to a soil and how it influences native plant management and the value of soil amendments such as compost in influencing the management of native and exotic plants. To my knowledge none of those questions have been answered. Our soils typically are not classified as sodic soils but there are pockets (areas) of them in the valley. There are also pockets of high boron (a soil salt).

 Other terms used besides Winter Deciduous include semi evergreen. It just means when it gets cold enough, it might drop its leaves because they get damaged by freezing weather, In warmer climates than Las Vegas, or if Las Vegas gets a winter with little to no freezing temperatures, then the leaves aren’t damaged by the cold and they don’t get damaged or may not drop.  A change in leaf color to a “bronzing” yellowish brown can also occur. This is also a signal that it got cold.  To reduce the chance of freezing damage, stop applying fertilizers to plants by around July 1. This winter air temperature became so cold in this North Las Vegas location that this mesquite tree leaves were damaged, but not the tree, and they dropped. This tree, sometimes also called semi-evergreen, became deciduous. If it gets cold enough, plants like this Star Jasmine will get yellow or bronze leaves and may even get deciduous. Sago palm can also get cold damage during the winter if temperatures get low enough. Bottlebrush can also get damaged from cold if winter temperatures are low enough. Cold or freezing damage can also occur to some plants like this myoporum (locally called Australian Racer). It depends on how cold it got and for how long.

  Orchard at Ahern in Las Vegas The Orchard at Ahern, located 1 ½ miles from Las Vegas Boulevard near the Center of Las Vegas, is looking for a responsible, experienced gardener, part time, to care for its vegetable and herb growing area. Ahern also owns and operates the Ahern Hotel in Las Vegas. The successful candidate would report to a Senior VP at Ahern and be responsible for the planting, growing, harvesting, and distribution of vegetables and herbs from its garden. Hours are flexible and the salary is negotiable. Interested individuals should contact Bob Morris at [email protected] with their contact information and experience.