Easterners live in a region which includes beautiful azaleas, camellias, roses and similar plants. These acid- loving plants thrive in the Eastern soils which are acidic. These plants are adapted for Eastern soils and struggle in the Western soils which are alkaline and arid.
Until recently, many Westerners settled for commonplace landscapes which include turf and bird of paradise. Now “curbside appeal” is desired in landscaping and can be had with azales, ligustrum, rododendron, rose, liquidamber and other acid-loving plants which do make a positive statement. The success of these plants in the West may be a challenge, but success is possible by understanding the needs of acid-loving plants and implementing proper soil-preparing and planting procedures.
Acid-Loving Plants Have Special Needs
(1) Available Iron – Acid-loving plants are quite susceptible to iron chlorosis, a deficiency of iron which results in yellow leaves, reduced new growth, reduction of inflorescence, and eventually death. Ironically, the problem is not of insufficient-iron in the soil. The fourth most abundant element in the soil is iron – the average content is 5%.
Most dicots plants makes nutrients available by plant-induced acidification of the soil around the roots. Acid-loving plants being adapted for acid soils, do not need a strong ability to lower the soil pH and have a weak ability to do so. Dicots from arid regions are much more efficient in acidification. Iron in alkaline soils has precipitated and has been made very unavailable. You are probably familiar with this problem unknowingly.
Have you every tried to wash oxidized iron sulfate off of a sidewalk? Plants have to assimilate this form of iron to be green. Iron sulfate helps plants until it precipitates in the soil. This may be a day or two. What really helps plants are the methods to optimize plant root acidification. These are better soil aeration, better drainage, lower salinity and better selection of fertilizers.
(2) Reduced Stress – Generally, acid-loving plants are sensitive to excess soluble salts. Since their native habitat is in regions with high rainfall which incidentally causes the acidification of soils, they are not adapted to the arid west with higher levels of salts. Soil preparation must provide for excellent porosity in order to have efficient leaching not only of initial concentrations of salts present at time of planting but also of the salts present in the irrigation water. This factor is usually more critical when the water source is from wells, certain rivers (such as the Colorado River) or from water reclamation projects.
A second factor which is also remedied with excellent porosity is that of aeration of the roots. These plants require good drainage for the rapid replenishment of oxygen following irrigation. If daily irrigation is practiced, plant roots may never have sufficient oxygen without using enhanced procedures for improving the soil. With good aeration. these plants are much more able to acidify the soil for solubilizing the iron.
(3) Acidic Fertilizers – Acid-forming and acid based fertilizers can be used to help acidify our alkali soils. Complete acidification takes time, if the soil is calcareous. The time can be decades. Soil sulfur can be used although there are some major limiting factors. Two-thirds of arid soils do not contain the microbes to oxidize sulfur. Sulfur oxidation occurs readily in acidic soils.
Even with the proper microbes, the oxidation rate is slow unless the soils are acidified. It may take more sulfur than which is cost effective to solve the problem. If soil contained just 1% calcium carbonate, it takes 147 pounds of sulfur to fully neutralize the alkalinity 6 inches deep per 1,000 square feet. If not all the calcium carbonate is neutralized, the soil is still calcareous. Some soils contain as much as 80% calcium carbonate.
Maintenance fertilizers need to be selected for the desired pH alteration. Calcium nitrate will increase the soil pH, ammonium nitrate and urea will be neutral mostly while ammonium sulfate will be acidifying. Periodic soil testing should be done to avoid over adjustments.
A new method to provide available iron entails acidifying several small locations near the rootball with dry, very acidic fertilizers. This can provide all the iron requirements for many years. Very acidic fertilizers are about to be produced.
Solutions for Transplanting Acid Loving Plants
Current methods of using large quantities of peat moss, nitrogen-stabilized redwoods and other organic materials have not been without problems. Water movement across the interface between the native soils and the amendments causes some problems sometimes resulting in a perched water table. It is best to use a backfill which is similar to the native soil. This can be done by using native soil with small amounts of organic materials in conjunction with polymer soil amendments which prevent soil compaction.
Soil Amendments can be used on native soil to impart topsoil-like qualities while having no negative interactions and give excellent aeration and water drainage. The cost of this technology is about half of the high organic amendment approach. Much can be done with advanced techniques to solve most causes of failure with acid-loving plants in Western soils.