Orange tree growing in southern Nevada Winter Low Temps First of all, citrus production is not commercially done in southern Nevada. There are two good reasons for that. Citrus are subtropical and range from fairly tolerant of winter freezing temperatures (kumquat, Myers hybrid lemon, grapefruit and mandarins) to citrus that can barely tolerate freezing temperatures at all (sweet oranges like Washington Navel, limes, true lemon). Commercial citrus production occurs in Yuma, Arizona, and parts of southern California where it is warmer.  Whether citrus survives the winter depends on the type of citrus, how cold it gets during the winter, if these minimum temperatures occur in spring, midwinter or fall, and how many hours it lasts.  Sweet orange is tender to winter low temperatures in Las Vegas. Here the sweet orange died back to the more tolerant sour orange rootstock and it grew replacing the sweet orange. The second reason citrus fail to produce fruit here is, like any fruit tree, due to late spring frosts when it is flowering. Flowers, unlike the tree, can’t handle any freezing temperatures or the flowers die and dont produce fruit. ‘The tree might be able to but the flowers can’t.  Flavor Supreme pluot in full bloom. The flowers of flavor supreme pluot and when they bloom make this tree irregular in consistent fruit production, year after year, in southern Nevada. Citrus like Meyer lemon can be the same. If a light freeze occurs once during its flowering time, there is a chance some fruit will be produced. If light spring frosts occur repeatedly over a couple weeks of flowering then it is likely there wont be any fruit produced. If a heavy spring freeze occurs then the whole crop is lost and maybe even the tree! Flowering is Triggered by Stress Draping burlap over citrus tree for cold protection in Las Vegas. Draping burlap over the tree keeps the wind off of the tree and may help reduce flower freezing by a couple of degrees. . But homeowners buy citrus from Las Vegas nurseries, plant them and wonder why they die or don’t produce fruit. Flowering in citrus is triggered by stress, whether it is from cold or drought. The plant doesn’t care. Both are forms of stress for the plant. In southern Nevada orange, grapefruit and mandarin characteristically flower for 2 to 4 weeks following winter dormancy or cold. Flowering starts just before a spring growth flush of leaves, commonly seen here in March. Out-of-season flowering is occasionally seen in June or August following a dry period.  Sucker growth from trunk of Cara Cara Orange in southern Nevada Lemons and limes also flower in the spring but may flower intermittently throughout the year. Kumquat does not produce flowers or have a spring leaf flush of growth until about May so it typically will have fruit regardless. On top of that it is one of the more cold hardy citrus you can grow in southern Nevada. Flowering will occur after a rain similar to a drought-induced dormancy in the tropics. There is often a main flowering period with the onset of rain after a long dry season and a small flowering period following the end of a rainy season when there are intermittent short periods of drought and rain. Citrus leaves yellowing due to intense desert sunlight Drought and Cold are Both Stressors In Nevada orange, grapefruit and mandarin characteristically flower for 2 to 4 weeks following the winter dormancy. Flowering starts just before a spring growth flush of leaves, commonly seen in March. Out-of-season flowering is occasionally seen in June or August but that is following a drought and then and rain or irrigation. Lemons and limes also flower in the spring but may flower intermittently throughout the year. Kumquat does not produce flowers or have a spring leaf flush of growth until about May. Flowering will occur after a rain similar to a drought-induced dormancy in the tropics. There is often a main flowering period with the onset of rain after a long dry season and a small flowering period following the end of a rainy season when there are intermittent short periods of drought and rain. Hobby St. Denis and grapefruit tree in Las Vegas, 1995 Flowers Produced at Different Ages Orange and grapefruit trees require 6-12 years to flower and fruit after planting young trees. Pistachios will be about the same. But grafts from the flowering portion of an older tree takes only three or four years! But the lower, older portion of that young seedling tree remains juvenile forever in exchange. Mandarins take only 5 years to start flowering, limes only 2-3 years and Key lime 1 to 2 years.  Once fruiting, most citrus are notorious for producing a smaller yield the following year after a full load of fruit. An example is the Murcott variety of mandarin. I tell people to not delay harvesting fruit from Myers lemon when ready because keeping fruit on the tree for a long time can result in smaller yields the following year. Myers lemon is ready to harvest in Las Vegas at the end of December to mid-January. When it is sweet to the taste, harvest the fruit. Pruning Citrus and Fruiting Pruning may delay flowering and fruit to the following year if its severe. It depends on the variety and how much pruning is done, but expect little to no flowering when trees are heavily pruned. Pruning citrus is done commercially to oranges and necessary for controlling the size of the tree and producing fruit regularly. But prune citrus with caution. Pruning can commonly result in reduced fruit and flowering on pruned portions of the tree. Annual or even every other year lightly pruning of the tree may be enough. Published research on best practices for pruning citrus is sparse.   Leaf loss due to winter freezes can decrease flowering and fruit production. Occasional leaf loss due to winter or spring freezing temperatures may not be a problem but regular early

The major uses of pine trees in desert landscapes are for visual barriers, sun protection, windbreak, or mark property boundaries.  Problems with Pines They oftentimes become too large for the property. Cute when they are small. That is the problem now, they are large trees so you need a lot of space to grow them. And they use more water as they get bigger. And they need to be watered deep to improve their anchorage during strong winds. There are plenty of other choices that are smaller trees for shade and for visual barriers. As windbreaks? Put windbreaks close to where they are needed,  not on boundary lines. Pine trees are frequently planted for shade but out of scale when they mature. The two pine trees most commonly planted here, are the more formal looking Afghan (Pinus eldarica, sometimes called Eldarica or Mondell or Mondale pine) and the loosely structured and informal Aleppo pine (P. halapensis). Aleppo vs. Mondell The less formal looking Aleppo pine (P. halapensis) The more formal looking, Christmas tree-like, Mondell pine (P. eldarica) These can be fairly large trees at 40 feet tall and above and can easily dwarf a single story home. They can use quite a bit of space and, at those sizes, can use quite a bit of water when they get bigger. Its not a question about whether they will grow in the Mojave Desert but where will you put them? Aleppo Pine Blight They can look quite similar sometimes and telling them apart can be difficult. All pine trees can cross pollinate and are wind pollinated. But most of the time they are easy to recognize. One method I use to differentiate the two is the presence of winter physiological disorder called Aleppo pine blight. It only is present on Aleppo pine. It usually causes isolated browning of new growth in a patch or two here and there. In some cases, it can cause tree death but it is rare in Las Vegas. Aleppo pine blight occurs during the winter and is a disorder that oftentimes causes isolated browning of new growth in Aleppo pine only. It can get so bad in some regions that it causes severe browning and suspected of tree death. Chir Pine? A vert large (60+ feet) and graceful pine sometimes used is the Chir pine (P. roxburghii). But this pine is a bit tender to winter cold (and in severe freezing temperatures (low 20’s) can be damaged. Like many other plants, in its wild native habitat in the lower elevations of the Hindu Kush (northern India, Afghanstan and northern Paksistan) survives fire and will “sprout” new growth from its trunk if scaffold limbs are killed by fire or cold. Not to be confused with a very similar looking, long needled, but more winter tender pine called Canary Island pine (P. canariensis) heralding from…you guessed it…the Canary Islands. Chir pine, considered perhaps subtropical, can be a bit tender in the Las Vegas area but it has a very graceful appearance if it survives the winter cold every 15 years. Chir pine is one of the “long needled” pine trees that can have a very graceful appearance in the landscape but not nearly as tender as its very close relative, the tropical Canary Island pine and similar in cold hardiness to some of the more tender citrus like naval orange (P. canariensis) This Chir pine survived but some of the branches froze. The mass of its trunk survived the freeze and sent out these suckers from epicormic buds embedded in the trunk. Fire and freezing temps can cause the same reaction. Japanese Black Pine Japanese Black pine is oftentimes recommended for planting in urban landscapes because it is a smaller pine (25+ feet) with an interesting form for landsapes. But when was the last time you saw one growing here? Nearly all of them planted here have died. Beware! Japanese black pine. Two Nevada State Trees Bristlecone pine (P. longaeva) and Pinion pine (P. monophylla) are the two state trees of Nevada. Pinion pine occurs at around 4500 foot elevations in Nevada. Bristlecone pine much higher. For this reason, Pinion pine would  have a better chance in the hot, lower elevations of the Mojave Desert than the 6000+ foot elevation Bristlecone pine. Pinion pine occurs in the wild along with Utah juniper. The problem? Availability. It was popular for Mojave Desert landscapes about 25 years ago and disappeared from nurseries. If you choose to grow pines in the desert: Give them plenty of room to grow because they will be big trees. Amend the soil in every direction around the trunk about 2 to 3 feet and a foot deep. Cover the soil after planting with 3 to 4 inches of woodchips. Water them with a coil of drip tubing or basin filled with water.  Water them deep when you water – three feet deep!

Sunlight can be very strong in the desert. In other parts of the country where sunlight is more “normal”, shade cloth might not be needed. Desert sunlight can be very intense at times. It makes sense with some plants to reduce light intensity with shade cloth? But how much? Which plants? Intensity The effects of sunlight (or light) can be broken down into the quantity of light plants receive and the quality of this light. Light quantity refers to its intensity, or how strong this light can be.  Intensity of sunlight refers to the quantity of light plants receive. Some vegetables give us better plant parts with a little bit of shade. This is 30% shade which is about right for a lot of leafy vegetables growing in the intense desert sunlight. This may be too much shade for some flowering vegetables like okra. The 30% shade cloth was doubled over to give 60% shade in this darker area of the grow tunnel. Usually anything above about 40% shade will prevent a lot of vegetable growth and production. Light Color The color of light can also affect plant growth. Red light promotes flowering while solid blue light discourages flowering. Research has demonstrated that different colors of light in combination can promote certain types of plant growth. Should you as a homeowner use different lights? Probably not but it might be worthwhile if you grow plants commercially. For more information look at https://sensing.konicaminolta.us/us/blog/can-colored-lights-affect-how-plants-grow/ At Dave Wilson Nursery near Modesto, CA, here red shade cloth is applied to influence plants. How Long Light Shines (Photoperiod) Plants will do different things sometimes at different times of year (mostly in cold climates, rain can play a similar role to light in tropical climates). Sometimes this is tied to how much night time there is or how much rain. Plants cant move around so they are much more “in tune” with their environment and “reading” it. At this marijuana production facility light is used to provide the energy needed for plant growth. A certain light intensity is needed if any kind of production is needed. Although not done here, a specific color of light could be used that enhances root production of these cuttings. Some decisions are better made considering the economics of production.

 Yuma AZ is warmer than Las Vegas. Yuma sits on the border of Arizona and Mexico. Its latitude sits between 32 and 33 degrees North latitude (Las Vegas is closer to 36 degrees north of the equator).  Yuma’s elevation is only about 140 feet above sea level (Las Vegas is about 2000 feet above sea level). Both elevation and latitude play major factors in determining winter low and summer high temperatures. Latitude and Longitude map of Arizona. Yuma AZ is near the border with Mexico and at 140 feet of elevation above sea level. Tucson AZ, even though lower in latitude than Yuma, is at 2400 feet of elevation above sea level which accounts for most of  its colder winter temperatures and warmer summers. https://www.mapsofworld.com/usa/states/arizona/lat-long.html Because of its warmer winter temperatures, Yuma can grow some of the more tender nopales (such as Copena V1 and F1 and better tasting!) from Mexico than we can in our colder winters in Las Vegas. We can grow cold hardy nopales but they are not as tasty as the more tender Copena types. Winter freezing temperatures affect both pad (nopales, nopalitos) and fruit (tuna) production. Freeze damage to Copena nopales growing in Las Vegas during the winter of 2007-8. To make the planting/harvesting adjustment from Yuma to Las Vegas, consult local temperatures but it will be about 6 weeks forward in the spring months and about 6 weeks backward in the fall months. Even though this crop calendar is for seed production, the planting dates would be the same.  “Contracting” refers to the business arrangements needed for seed production to begin. “Sowing” refers to planting time. https://www.condorseed.com/contract-production/ 

 Come join me in this podcast about exploring Food Forests in the Desert. Should we pursue this permaculture concept in desert landscapes? Moringa leaves on our farm in the Philippines. We use the leaves of this tree for food and as a spice nearly on a daily basis. They are a commonly planted tree now in Southern Nevada due to food forests. But is it the right thing to do?

Q. Our bottle tree in Scottsdale is 11 years old and this summer had a crazy amount of leaves dropping. So, we watered longer but only once a week. It also gets some water when the lawn is watered, and right now, that is 3 times a week. The leaves are very, very light green, turning brown on the edges first and then completely brown and then dropping leaving it very sparse. Are we not watering long enough, or is it getting too much water? Bottle trees sold in the nursery are not really a bottle tree. Yes it has a tapering trunk but the REAL bottle tree has a trunk shaped like a bottle! It may drop its leaves naturally when the soil is dry or just before it starts to flower in the late summer or fall. The true bottle tree (B. ruprestis) has a much fatter trunk, shaped like a bottle. A. These trees normally drop leaves just before flowering at the beginning of their wet season. In Australia where they are native, that would be just before our fall months. Many “south of the equator” trees don’t pay any attention to their new environment and flower or drop their leaves just like they were growing south of the equator. If leaf drop occurred starting around September and got worse a few weeks later, their leaf drop may be a response to longer nights, something totally out of your control. Maximum/minimum temps in Scottsdale, AZ, USA. Maybe it Was to Hot Our normal summer temperatures are are about 10F hotter than their maximum high temperatures where they grow naturally. In their natural environment, the beginning of Australia’s monsoon season mean cooler temperatures. With these high temperatures and low humidity and if there was a some wind then it would mean the plants and soils would dry out sooner. Your tree may have got hit with a double whammy; high temperatures and intense sunlight. You did the right thing. You increased the amount of water they received by increasing the amount of water and not the frequency of water application. The only thing I would add is to increase the area where water is applied and not just the amount while all the time not letting the soil dry out between irrigations. My guess is the tree was getting most of its water (and fertilizer) from the lawn. That’s also probably were most of its roots are growing. These trees like to have their “toes” in water but not submerged. Next time this happens, try watering your lawn a little more often. I think the amount of fertilizer the lawn is getting is plenty for this tree.

Q. I have several bottle trees that have grown well over the last years and one that has always had a slight “droop” to the branches. I’m not sure what else to do as all the other trees are doing great! When young, many trees have upright growth. It is very common in young trees. Remember, Kurrajong (aka Bottle tree in the US) can reach 55 feet tall! A. If the tree otherwise looks healthy there may be nothing you can do about it. Growers of bottle trees usually start them from seed. Propagating plants directly from seed creates a lot of tree variability in their growth habit, flower color, seed pod as well as the seed itself. The result is that some trees are more upright than others, some have different leaf color, and some more resistant or susceptible to disease or insects. Its genetic and nothing much you can do about it. Trees grown from seed can show quite a bit of genetic variability in their shape, leaf color, overall size, size of acorns, leaf size and other visible traits. That’s not even counting what you cant see! Other trees propagated from seed include southern live oak, and most of our pine trees. So, you see, this variability can be good, or it can be bad if you don’t like it’s looks or it’s more susceptible to a disease present in your locale. If you are not careful in your watering, the canopy can drop leaves or maybe some limbs might sunburn and die. When trees are young, they oftentimes grow more vertically. They want to get taller and get taller than any competitors nearby. As they get older, vertical limbs become more horizontal. It’s possible this is what you see. When it has a full canopy of leaves then horizontal limbs are not a problem. The dense canopy of leaves shade these thin-barked horizontal branches. But if there is leaf drop from disease, insects, drought or normal leaf drop then watch for sunburn on these very susceptible limbs. Because they are native trees, they don’t need a lot of fertilizer. Native plants are like that. They are not commercial hybrids that rely on more soil nutrients applied by fertilizer. This means applying a light application of high nitrogen fertilizer like 16-16-16 or 20-20-20 once a year in the spring just after new growth starts is enough.

            I thought I would talk about “Bottle trees”. The reason for that? I get so many darned questions about them from readers. I get more questions from confused readers about this tree than any other landscape tree. These aren’t usually good questions; they are problem questions. All these problem questions makes you wonder if they should be planted in our warm desert at all! They should but choose a good planting location and water them carefully and not haphazardly. The true Bottle Tree, Brachychiton ruprestis, has a bottle-shaped trunk. The Kurrajong, B. populenum, has a straigter trunk and is oftentimes called “Bottle tree” in the US. (Picture sent by reader in Australia where they are native) What you are buying from the nursery (Brachychiton populneum) is not really a “Bottle tree” at all. The correct name is “Kurrajong”. The true bottle tree (B. ruprestis) is very different from the nursery version because its trunk is truly shaped like a bottle! It’s a beautiful oddity in the landscape. But the true Kurrajong hybridizes very easily with other types of so-called “Bottle trees”. The growers propagate “Bottle trees” from seed. Seed results from a cross between “mama” and “papa”. Unless the growers are knowledgeable, who knows what you are getting? The Kurrajong, (B. populneum) which we here in the US oftentimes mistakenly call a Bottle tree, does not nearly have the trunk taper of  B, ruprestis. Picture sent by reader in US.  The number one questions I get is about watering. They grow primarily in the dry interior of Australia. They are not a “swamp tree” and they are not a cactus but something in between. When you water them, think of them more like watering a palm tree (e.g., date palm) or even asparagus; they like to have their “toes” constantly in water but without the soil around them continuously wet or they will die. Be very careful of overwatering Bottle trees, any of them. It is a delicate balancing act of giving them enough water vs watering too often when planted near or in a lawn., Leaf drop can be normal. It frequently will drop leaves just before  or if it’s not getting enough water (that does not mean water it more often!) The horizontal branching and thin bark of the so-called Bottle tree can lead to sunburn if the canopy begins to thin due to leaf drop. Plant in the spring, not during the hot summer months. Unlike palm trees, they don’t grow well after planting during the heat. Yes, they should be watered more often after first planting; maybe twice a week in the spring or fall rather than once a week. But after one growing season, apply a lot of water to a large area under its canopy but water less often. This means either apply the water slowly as in drip irrigation or build a mound or moat around the tree to hold the water so that it sinks in the ground. Applying a lot of water at once uses the same amount because “little sips are combined into one big gulp”. Leaf scorch followed by leaf drop can occur because of watering too often or not enough water. Seldom is it from giving the tree too much water at one time unless the soil has poor drainage. Poor shade from the canopy can lead to sunburn of thin-barked limbs, particularly horizontal limbs. The second problem I hear about from readers is sunburn or sun scorch on their primarily horizontal limbs. Sunburn on the limbs is for two reasons; the first is because this tree has very thin bark easily sunburned by intense sunlight and the second reason is due to where it’s planted. Never plant this tree in the hottest locations. It’s not a mesquite, Cordia or sweet Acacia.

Q. I read your blog on pruning flowering shrubs but want to know if this information also pertains to wisteria vines? I’ve read that flowering occurs on new growth, so I am not sure about trimming it. A. In my blog I was telling people to differentiate between plants that flower early in the spring versus those that flower later in the spring. Bottom line, always prune flowering trees and shrubs any time after they finish flowering if flowering is important to you. Let me first give you a textbook answer. Wisteria falls into two major groups; the Asian varieties and the western varieties. The Asian varieties of wisteria flower on last year’s growth (early spring flowers) while the American or western varieties flower on current season growth (late spring or summer flowering). Something interesting about wisteria is the amount of time the plant needs to begin flowering. It’s usually quite a while. Some people say 10 years to initiate flowering, others say 15 years and I have even seen some people say 20 years! That’s actually quite old for a woody plant to start flowering. Typically unimproved woody plants begin flowering in about 6 to 8 years.  Plant breeding and producing hybrids that flower earlier can address this problem. When you’re pruning try to leave as much older and larger wood as possible. Prune its structure the way you want it as early as possible. A few things that can affect how soon or at what age the plant begins flowering can be removing too much larger wood, using a lot of high nitrogen fertilizers, how much shade it’s growing in to name a few. It will flower when it’s good and ready to flower. Just remember prune after it finishes flowering and you won’t go wrong. Fertilize once a year in the very early spring with a “rose fertilizer” and not a “lawn fertilizer” or apply compost in the early spring.

Q. I am reaching out to you to see if you could offer some advice on my established fig tree. I noticed that some of the leaves have turned yellow with browning at the end and are drying off. The tree seemed to be healthy up until the last couple of weeks. The fruit seems to be in good shape.   A. The fig tree appears to be okay except for a few yellow leaves. The picture you sent shows the yellow leaves in the shade or interior of the tree. That could be normal if the leaves are not getting enough sunlight they will turn yellow and drop. The most important thing is the growth of the tree and fruit production. You haven’t mentioned it’s growth but the fruit production seems to be good from what I understand, another indicator that the tree is healthy. There doesn’t appear to be a problem except the yellow leaves in the shade in the center of the tree. For those reasons I would tell you that there isn’t a problem. I would suggest however that you keep the grass away from the base of the tree two or three feet. Dig out the grass from this area and cover the soil with wood chips. Rock would not be a good idea there. Do not plant annual flowers in that area but you could put a circle of edging around the tree to contain the mulch. I would not plant anything in the mulch area but keep it free of weeds. The fig tree will get plenty of water and fertilizer because of the lawn.  It will not need anything extra. Make sure that the lawn is not getting so much water that it harms the tree.