Problems with Acidic Soils: Lime Can Work Wonders

Note: pH is the measurement of the soils acidity/alkalinity. The pH scale is from 0 to 14 with 7 as the neutral point; below 7 is acidic, above 7 is alkaline. Here are a few common pH examples:

• Extremely acid:  lemon-2.5; vinegar-3.0; stomach acid-2.0; soda pop-2–4

• Strongly acid:  carrots-5.0; asparagus-5.5; cabbage-5.3

• Slightly acid:  cow's milk-6.5

•  Neutral:  saliva-6.6–7.3; blood-7.3

• Slightly alkaline: eggs-7.6–7.8

• Moderately alkaline: sea water-8.2; sodium bicarbonate-8.4

• Very strongly alkaline: soapy water-12; household bleach-12.5

Concerning the pH of soils, there is a preferred range in which plants will grow best. Most soils in Hawaii, as in other parts of the country, are acidic. Extremely acid soils can have a toxic effect on many plants. One common problem is excessive aluminum and manganese becoming soluble in the soil adversely effecting plants.  Acidic conditions can also change the type of microorganisms living in the soil. This will affect the amounts of nitrogen, sulfur and phosphorus available to the plants since the microorganisms breakdown these nutrients into plant-available forms.

These acidic soils will benefit when lime is applied. As an amendment, lime in its various forms can raise the pH of the soil and eliminate a number of problems.

Ground limestone is almost pure calcium carbonate and comprises the largest percent of lime used in the United States. It is usually the cheapest form of lime. Limestone with significant amounts of magnesium carbonate is called dolomitic limestone (dolomite), containing approximately equal parts of magnesium and calcium carbonate. Dolomite works well especially if the soil has a magnesium deficiency.

Hydrated lime, another form, is one and a half times more effective at raising the soil pH but is also more caustic, and therefore,  hazardous to handle. Protection for the skin and lungs is recommended. Excessive amounts of hydrated lime can cause a pH shift towards a highly alkaline condition. Conversely, when using dolomitic lime, it is difficult to apply too much as long as it is thoroughly mixed into the soil.

When purchasing lime, a fine powdered lime, about 60-100 mesh, is the fastest acting grade available.  However, being a fine powder, it is a potential eye irritant under windy conditions. It will also cake rather easily, and when improperly mixed, it will stratify forming a layer that can burn roots and repel water.

A coarser limestone (similar to salt grains) is also available and is easier to handle, but its disadvantage is that it is slower acting.  In summary, incorporating lime as an amendment in any of its forms can make a big difference in acidic soils.

pH Can Make A Difference

Why are certain plants in the garden growing poorly while others flourish?  
Obvious answers maybe insect pests, fungal diseases and abiotic ailments such as soil deficiencies. The pH of the soil, however, is an often overlooked problem. pH measures the acidity/alkalinity of the soil. Seven is neutral; below 7 is acidic and above is alkaline.

To address this, the University of Hawaii Cooperative Extension has a publication “The pH Preference of Plants.”  The pamphlet includes a chart with many crops including fruit trees, vegetables and ornamentals, and their suggested pH growth range. All plants prefer a specific pH range, usually around neutral; some require slightly acidic while others favor slightly alkaline.

The pH of soil is important and can be a reason for poor growth. Take note which plants are doing well and which are not. Compare those plants to the list in the publication. If all or most of the poorly growing plants prefer a soil pH which is not indicative of your soil, then pH may be a problem. Get a soil analysis. Often taken through a local university cooperative extension, the analysis will be  helpful for a variety of reasons.  

As an example, breadfruit, mac nuts, parsley, lilikoi (passionfruit) and gardenias prefer an acidic soil and will grow well down to a pH of 5 and even 4.5.  These plants may be flourishing in the garden,  On the other hand, plants like bananas, mock orange, broccoli, leeks and lettuce all like a pH much higher, between 6 and 7. If these plants are growing poorly, then your soil may be too acidic.  

For additional information on pH and a useful chart, search this blog for the articles, Problems With Acidic Soils: Lime Can Work Wonders, and Unsuspected Causes of Plant Damage.

Ways of Adding Phosphorous to the Soil

 Primary nutrients of plants include nitrogen, phosphorus and potassium; they are the ones indicated on each fertilizer package. For example, 5-10-15 printed on the label signifies that the fertilizer contains 5% nitrogen, 10% phosphorus and 15% potassium.

Many soils are deficient in phosphorus, especially those red Hawaiian soils high in iron and aluminum oxides.  When growing vegetables, or any annual crop, phosphorus can be incorporated into the soil before the crop is planted. It can also be incorporated before trees and shrubs are planted. The difficulty comes when attempting to apply a phosphate fertilizer to an established tree or shrub with existing roots already deep in the soil.

In contrast to nitrogen fertilizers which are water soluble and move well in the soil, phosphate fertilizers do not move well. In fact, years after a surface application of a phosphate fertilizer, the majority of the phosphorus will still remain near the soil surface. How then can a phosphate fertilizer be applied and penetrate down to the roots of mature trees?   Here are some better ways of applying a phosphate fertilizer to existing plants. 

1. Remove a core of soil at the drip line of the tree, at the four corners, 1 – 2 feet deep. Cores can also be removed going around the drip line of the tree in a circular manner. Apply a measured amount of phosphate fertilizer to these holes, either dry and mixed with soil, or in a water solution.  Ammonium polyphosphate is especially good. Admittedly, this involves a good deal of labor when treating many trees. 

2. Similarly, fertilizer spikes, although expensive, can be placed in the ground around the drip line. In both cases, roots will gradually gravitate to the higher nutrient content and flourish.

3.  Foliar applications of a phosphate fertilizers do not work well. Frequent applications of 3-4 times per year, however, can potentially meet the trees requirement.

4. Perhaps the best alternative in improving phosphate availability and movement into the soil is to apply it in its organic form; for example, manures, fish meal and blood meal. Likewise, adding organic mulch is beneficial. As the organic material breaks down, the end product is humus. Humus is loaded with negatively charges sites that are able to hold onto positively charged plant nutrients such as potassium, calcium, magnesium, manganese and iron. Keeping the tree under a bed of mulch will supply a small but constant supply of various essential nutrients.  Roots will eventually grow into the mulched area and proliferate, picking up essential nutrients. In addition, because of the abundance of new surface roots in this area, it now becomes an ideal place to apply a phosphate fertilizer.  

Fertilizers - Nourishing the Garden

Which is the best fertilizer? With the countless number of fertilizer products on the market, little research has been conducted to show whether there is significant differences among the various brands. If you have found a particular product that produces outstanding results, and you are willing to pay the price, then by all means, continue to use it.

Otherwise, let me give you some fertilizer basics. In the broadest sense, nitrogen is nitrogen (N), phosphorus is phosphorus (P), and potassium is potassium (K).  Plants only absorb nutrients that have been broken down into inorganic, water-soluble forms.  For example, whether nitrogen comes from brand A or B, whether it was derived from anhydrous ammonia (gas) or urea, or from manure or the compost pile, it makes no difference to the plant. Stick with a basic N-P-K fertilizer, buy on sale, and don’t fall for promotions.

The question now is what type of formulation to purchase?  Nitrogen only, potassium only, phosphorus only, or combinations?   Nitrogen is always needed in areas of heavy rainfall, because it is easily leeched out of the soil.  Fertilizers like ammonium sulfate, ammonium nitrate, urea and calcium nitrate are all good fertilizers for supplying nitrogen. Calcium nitrate will also give calcium but is more expensive. 

Like nitrogen, potassium can also move in the soil with water; phosphorus moves very slowly. The question of whether to apply potassium and phosphorus can be answered accurately by a soil analysis.  Without an analysis, statements about soil fertility are only guess work. Check with local university cooperative extension offices for information about soil analysis.

 If an analysis is not taken, then buying a fertilizer with all three ingredients (N-P-K) is a good idea. The only problem with that is if the soil has adequate phosphorus, and over the years more is added, a soil imbalance may occur, and the excess phosphorus will cause a deficiency in iron and zinc - seen as interveinal chlorosis, a yellowing between the veins.  Also, it is cheaper to supply nitrogen than all three nutrients. On the other hand, you can apply nitrogen alone and supply the potassium and/or phosphorus only when deficiency symptoms occur.

Sometimes micronutrients are added to an N-P-K formulation. But they are added at such low amounts that they are seldom beneficial to the plant, especially trees. If a micronutrient (zinc, manganese, magnesium) deficiency truly occurs, buy that specific nutrient and apply to the soil or as a foliar treatment, whichever is appropriate. Special formulations of ‘citrus food’ or ‘avocado food’ or ‘palm food’ are good fertilizers. But note that they are higher priced, and a basic all-purpose (N-P-K) fertilizer should work as well.

Organic vs. Inorganic

Inorganic fertilizers often contain rather high percentages of the major nutrients and are applied on a per pound per acre basis. Organic fertilizers, on the other hand, have relatively low amounts of nutrients and are applied on a per ton per acre basis.  Although organic fertilizers have many benefits - including improving soil structure and the water holding capacity of the soil, feeding beneficial microorganisms and  of course, acting as a reservoir of nutrients that can be released to the soil - they are rather expensive in some places like Hawaii.  Gardeners, however, are encouraged to take advantage of any free or inexpensive supply of organic fertilizers, i.e., manures, in their area.

A Case of Too Much Nitrogen

Why do fruit trees have dark green leaves but bear little or no fruit, especially if they are well fertilized? 

Here is a brief lesson in plant nutrition: in general, nitrogen is for vegetative growth. Consequently, when fertilizing a lawn or any plant grown primarily for its leafy growth, the main nutrient to apply is nitrogen. When growing plants for fruit or flower production, as opposed to foliage, a balanced complement of phosphate and potassium needs to be applied along with the nitrogen. Applying large quantities of a high nitrogen fertilizer to fruiting trees like citrus and avocado will put them in a ‘foliar growth mode’, producing an abundance of dark green leaves but little or no fruit. Be careful how much high nitrogen fertilizer you apply to the plant.

Urea fertilizer contains 46% nitrogen, ammonium sulfate 21%, while manures in general contain less than 5% nitrogen, usually around 2%. For more precise instructions on fertilizing fruit trees, CTAHR has a short publication titled Fertilizers for Fruit Trees in the Home Garden #37. It can be accessed online or at UH CTAHR Office at 875 Komohana St, Hilo, Hawaii. Other state extension offices in the U.S will have similar publications.

Beware: Fertilizers Can Burn Plants

If you water plants with ocean water, the salts in that water would eventually accumulate to a level that is toxic to the plant -- assuming a good rain doesn’t come each night to leach out these salts. Whether its ocean water, manure, or fertilizer, each contains salts that can accumulate to a toxic level. Salts are not just sodium and chloride found in ordinary table salt. The nitrates, phosphates, sulfate, etc., found in fertilizer and manures are also referred to as salts. As an example, one cup of calcium nitrate fertilizer may be recommended for a large tree and one tablespoon for a small shrub.  Do not think that if one cup or one tablespoon is good, that two are better.  No matter how good a fertilizer is, too much, can burn and even kill a plant. When plants are over fertilized, in approximately one to two weeks the tips and edges of the leaves will begin to turn brown.  With a slight overdose, tip burn may be all that occurs. A larger overdose will cause many or all of the leaves to turn brown and drop off.   Eventually, as the excess fertilizer is leached out (diluted and carried below the root zone), the plant will put forth new roots and new leaves.

Handle fertilizers with care.  Used properly, they will nourish plants; overdosing can cause injury. 

Don’t Pile Mulch Against Tree Trunks

Applying organic mulch to the garden provides many benefits: improves the soil structure, adds micro and macro nutrients to the soil, conserves water during a drought, and acts as a food source for many beneficial microorganisms living in the soil. When applying mulch around trees, however, an air space must be kept between the mulch and tree trunk so the bark can dry. A constantly wet trunk will provide a suitable environment for disease. This, of course, does not apply to all trees. For instance, the magnolias of the Southern States grow along streams and swamps.  But other trees, like citrus and avocado, are susceptible to crown rot.    If the fungal organism is present and the bark remains wet for a prolonged period of time, infection will occur.  Untreated, the tree will die. Don’t pile mulch against the tree, and don’t position sprinklers so the water hits the trunk. Keeping the tree trunks dry as much as possible is important. In general mulch enhances the health of trees but precautions need to be observed.

What’s Crawling in the Compost Pile?

          

There is truly an abundance of living creatures that inhabit compost piles.  They range from slugs, centipedes and beetles to tiny microorganisms like fungi and bacteria; some can be seen but most cannot.  Some of the giant inhabitants may be toads and rats.

 The insect population of compost piles will include ants, beetles, cockroaches, centipedes, earwigs, millipedes, sowbugs, springtails and termites as well as flies laying their eggs.  Some insects like earwigs and sowbugs feed on the organic matter; springtails and some beetles like fungi to eat, as do ants; termites, of course, eat wood, and cockroaches like decaying wood.

Spiders and tiny mites are eight legged creatures classified as arachnids rather than insects.  Spiders feed on other insects while mites feed on many things including decomposing plant material, nematodes and fly larvae.

 

    Nematode on plant root

Some nematodes are garden pests, infesting ornamentals and edibles.  But many are helpful and thrive in compost piles.  They feed on decaying matter, bacteria, protozoa, fungal spores and other nematodes.  Earthworms are especially beneficial.  They help breakdown the organic matter, make N-P-K (nitrogen-phosphorous-potassium) available to the plants and help till the soil.