Thursday, March 31, 2011

Queen Palms - In Las Vegas???

Queen Palms  -  In Las Vegas???

Growing up in Southern California in the 70’s the Queen Palm was one of my favorite palms.  Of the many different species of palms growing in California landscapes the Queen Palm (Syagrus romanzoffiankum) provides one of the best tropical effects with its smooth straight trunk, soft bright graceful green feather-type fronds that sway with the slightest breeze. 

When I moved to Southern Nevada in 1979 I was quite surprised to find the queen palm being used in landscapes.  Environmental conditions of the Las Vegas Valley with colder winter temperatures combined with highly alkaline soils produce less than desirable growing conditions for this palm. 

March 2011 Las Vegas
March 2011 Las Vegas
Some degree of damage to frond tissue occurs nearly every winter.  Trees are hardy to the mid 20’s with death often occurring in the low 20’s to high teens.  During the winter of 90-91 official temperatures dropped into the single digits and nearly every Queen Palm in the Las Vegas Valley was killed.  In addition, Southern Nevada’s highly alkaline soils (high pH) severely limit the availability of the essential soil trace elements or nutrients required for proper growth and development, especially manganese.
March 2011 Las Vegas
March 2011 Las Vegas

The damage to the palms in the photos is not unusual. It's also important to note that this past winter was average or typical and would not be considered exceptionally cold.  Without TLC these palms will not generally recover replacing all the dead fronds until late summer when its only a short time until the process starts all over again.

So why do we still see Queen Palms installed every spring and summer in Southern Nevada Landscapes?  Because the palms are inexpensive, readily available from Southern California, provide a nice tropical effect, and are very attractive in nursery growing containers as they arrive in Las Vegas from Southern California.


Tuesday, March 29, 2011

Mexican Evening Primrose - 'Bug Alert'

Mexican Evening Primrose ‘Bug Alert’

With cold winter temperatures behind us and the onset of warm spring weather Mexican Evening Primrose can be found actively growing throughout the Las Vegas Valley with the plants soon to be in full bloom.  However, the warmer temperatures and lush new plant growth also brings out the flea beetle. 

Adult flea beetles feed on plant foliage.  They are very small insects between 1/16 inch to 1/4 inch long.  The color of the insects varies dependent on species with metallic bluish-black most common in our area.  Flea beetles often hide and are difficult to see without close observation of the plant foliage.  In most cases, the presence of the insects are first observed when the new lush foliage begins to look tattered.  The beetles can do a considerable amount of damage in a very short period of time.  The insect will decline in numbers with the onset of hot summer temperatures; however, a second cycle of beetles may appear once again late summer.

To keep your plants healthy and ensure an attractive spring bloom will require early detection of the pest.  Flea beetles are easily controlled with insecticides. 


Sunday, March 27, 2011

Mesquite - A Las Vegas Landscape Challenge?

Over 30 Mesquite trees in this Las Vegas parking lot were
blown over due to a strong summer wind.  Photos identify
 insufficient root development while considerable top
growth has taken place.

Mesquite – A Las Vegas Landscape Challenge?

In Southern Nevada we have been using mesquite trees in both commercial and residential landscapes for many years.  Found throughout the southwest, the mesquite is quite tolerant of Las Vegas environmental conditions.  Although there are different species, the Chilean Mesquite (Prosopis chilensis) and the Texas Honey Mesquite (Prosopis glandulosa) are most often the species of preference. 

Large beautiful mesquite trees that enhance our landscapes do not naturally occur, but are often a product of years of determination and hard work.  Mesquites do not grow naturally into upright single or multiple trunk trees with large full crowns.  In there natural environment trees are often found growing in thickets with their growth habit similar to a very large sprawling belligerent thorned shrub.  Young nursery trees require considerable training, mostly in the way of pruning and staking, to produce a saleable upright growing tree (notice all of the tree support stakes next time you see these container grown trees in the nursery).  As trees increase in size and their initial upright form has been established less work is required although not entirely eliminated. 

Poor root system development is another issue we are constantly dealing with in nursery container grown mesquites.  In the wholesale nursery growing environment mesquites grow very rapidly.  The trees are initially grown in small containers and are upsized or repotted to larger containers as they grow and develop.  With such rapid growth it is not uncommon for root problems to develop in terms of girdling roots and/or root-bound plants.  Trees with root problems may be upsized several times with the potential of the same problems reoccurring.  Although root development may be quick, top growth is generally faster.  Therefore, it is possible to not only have a tree with poor root structure, but one in  which the top growth far exceeds and is out of  proportion with the size of the root system.  Even  a nursery container tree with good root structure that is also in proportion with the tree’s top growth, when placed into a landscape environment where it receives frequent irrigation, fertilizer, etc. may once again experience top growth exceeding root development.  This is the reason we often see trees tied to support stakes for several years following installation. 

Loss of newly installed mesquites to winter desiccation is another problem common to Southern Nevada.  Most nursery trees are produced in Southern California and Arizona where winter temperatures are mild.  Planting of these trees in Las Vegas mostly occur during spring and summer months.  With warm weather, irrigation and fertilization trees grow rapidly producing soft tissue.  As often occurs with new landscape installations heavy irrigation continues into the fall and early winter and trees do not have an opportunity to harden off prior to the onset of cold and often freezing temperatures.  With lush growth, soft tissue and wind combined with cold temperatures desiccation and death may occur. 

Rules of Thumb (Green Thumb):

ü      The smaller the better!  Small containerized nursery trees are less likely to have root problems and will often out perform larger containerized trees.  Unfortunately, small container sizes such as 5 gallon are generally not available since the trees will quickly grow to 15 gallon or larger and thus have a greater cash value to the wholesale grower.  Always inspect the tree’s root system prior to planting.  Root pruning may be necessary to correct problems or deficiencies.

ü      Strong, healthy, upright, and attractive mesquites don’t just happen by luck!  Trees will also require considerable training following installation.  Put as much emphasis on developing a strong root system as you do on developing the above ground structure.  This may require heavy pruning of the top growth to keep it proportional to the developing root system.

ü      Don’t over fertilize.  In most cases mesquites require very little fertilizer.  Too much fertilizer will often increase top growth at a faster rate than root growth producing a top heavy tree.

ü      Irrigation system design needs to meet the newly installed tree’s requirements as well as the tree’s long term requirements.  Improperly designed irrigation systems can restrict as well as create rooting problems which may lead to eventual tree failure. 

ü      Keep installation of trees in turfgrass areas to a minimum.  Turfgrass irrigation and fertilization encourages shallow rooting and excessive top growth.

ü      Heavy pruning should only be done during the coldest time of the year.  Trees produce heavy sap flow during warm temperatures.  Large pruning cuts made during warm weather may produce sap flow to the exterior of the tree for months or in some cases years. 

ü      Don’t fertilize newly installed trees and reduce irrigation in the fall to harden off trees for winter. 

Friday, March 25, 2011

Purple Flowering Plum - Disappearing From Las Vegas Landscapes

Purple Leaf Flowering Plum (Prunus cerasifera)

During the past twenty-five years we have seen a tremendous decline in the purple leaf flowering plum trees across Southern Nevada.  The losses have been primarily due to the insect the flat head borer.  Today flowering plum is used in limited quantities in commercial landscapes with most tree installations occurring in residential landscapes.  The flat headed borer will continue to thrive in Southern Nevada and many more plums will be lost each year, especially trees that are stressed due to adverse cultural or environment factors. 

Keeping trees strong and healthy through good cultural practices including fertilization, irrigation, pruning, and pest control will greatly reduce problems with borers.  Trees should be fertilized mid to late February, late spring, and again early fall.  Irrigation system design should meet the needs of newly installed trees as well as meet the eventual requirements of a mature tree.  Trees should be professionally pruned each winter to ensure good structural development of the branches that form the crown but should also encourage good density.  Excessive thinning may promote sunscald of the internal branches which will encourage borer infestation. 

In addition to borers, purple leaf flowering plums are attacked by chewing-type insects and foliar diseases.  These pests along with poor cultural practices reduce leaf size thus increasing potential for sun scald of internal branches within the crown.  Proper cultural practices including fertilization in conjunction with two foliar applications of an insecticide/fungicide mix will greatly increase leaf size and overall density of the tree’s crown.  The insecticide/fungicide mix should be applied to the tree’s branches and foliage following spring bloom with the second application six weeks later.