Friday, November 30, 2012

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.

Tuesday, November 27, 2012

First Year Citrus Fruit - Remove it or Not?

This question comes up often in regards to young citrus trees. The answer is applicable to many fruit trees: trees spend energy in order to develop their fruit. For an older tree, there is usually enough energy to both grow the tree and develop the fruit. When a young tree produces its first bloom, there is a limited amount of energy. Will all the energy be used to grow leaves and branches or will some of it be applied to develop fruit? Many citrus growers will choose to sacrifice the first year’s crop - remove the young developing fruit - so their trees will grow quickly and eventually produce more fruit. 

On the other hand, if the first fruit is left until maturity, that fruit is using energy at the expense of the growth of leaves and branches.  For the homeowner, since the resulting differences in yields are generally small, my advice is to enjoy the first season and let the fruit set!

Friday, November 23, 2012

Diatomaceous Earth, An Organic Insecticide

 Diatomaceous earth (DE) is an inert dust mined from the remains of fossilized silica shells of certain algae known as diatoms. It is composed of approximately 3% magnesium, 33% silicon, 19% calcium, 5% sodium, 2% iron as well as other trace minerals such as titanium, boron, manganese, copper and zirconium.

As an organic insecticide, DE works in two ways to kill an insect. 1) It absorbs water-protecting fats and oils from the outer, waxy layer on the surface of the insect and causes desiccation or dehydration.  2) Being highly abrasive, DE scrapes and cuts the insect’s cuticle layer, contributing to more desiccation. However, it is virtually nontoxic to mammals.

Around the home, dusting the powder on the floor, carpets and crevices will kill cockroaches, silverfish, ants, and fleas.  Since the powder must stay dry in order to be effective, repeat applications may be necessary in humid areas. DE is more effective in drier climates. It is also used to control beetles where grains are stored.

The same basic principles used to kill indoor insects can be applied to insects which attack plants outdoors.  Some gardeners will dust plants with diatomaceous earth in order to kill insects such as aphids and beetles which feed on the plants. The problem with outdoor use is high humidity and rainfall.   When DE becomes wet, its effectiveness is diminished.  Dusting plants with DE is the most effective application method. DE dust can cause eye irritation so wearing goggles and a dust mask is recommended.   DE is moderately effective against slugs and snails as long as the material remains dry. 

 Insecticidal DE is not the same as the DE used in swimming pool filters. Other chemicals are added to pool grade DE, and the product is heat treated. This causes it to assume a crystalline form and is a respiratory hazard. Pool grade DE should never be used for pest control.

Tuesday, November 20, 2012

Watering House Plants

Many people have asked about the care of indoor plants, “How often should I water?” The answer I give will apply to plants in the house, in an office setting  or on the lanai or porch.

1)  Do not water plants by the calendar, even though it seems the easiest way. Using this method assumes that environmental conditions such as temperature, humidity, wind, etc., each day of the year will be the same.

2) Water by inspection of the soil. If the soil is wet, wringing wet, don’t water; if it’s dry, water the plant.  If it’s moist but not soaked, wait a few days and check again. If you actually observe the plant wilting, you should have watered yesterday! When assessing the soil, do not test the surface, which usually dries out rather quickly.  To truly evaluate the condition the soil of a potted plant, place your finger about a third of the way down the pot or take a mini trowel and pull up some dirt.  In reality, you may end up watering somewhat by the calendar, but you will have arrived at it through observation and inspection. 

3) The lifting method also works well. If the pot isn’t too big, simply lift the pot off the ground; if it’s heavy, it has plenty of water. In comparison, if it’s relatively light, it’s time to water. Putting these methods together, you’ll soon get the hang of it.

A major problem lies in the fact that wilting and slow growth can be symptoms of both under watering and over watering. In the case of over watering, the roots will begin to rot, with or without the help of soil pathogenic fungi. Once some of the roots are gone, the plant will not be able to pick up enough water, especially on hot days, and the leaves wilt.

Whether under watering or over watering, the leaves wilt. It is important to note that under watering a plant will lead to  non-vigorous growth and low fruit production for fruit producing plants, but over watering can easily lead to the death of the plant.

Knowing when to water will take some experience, and some trial and error.  It is important to use a well-drained potting mix and never leave water standing in the tray. (Discard the water; don't reuse it.) Plants that have been in the pot a long time may become pot bound, meaning that most of the space in the pot is occupied by roots rather than soil. If this is the case, you will find that these plants need very frequent watering, because there is simply no soil to help hold the water.

Friday, November 16, 2012

Growing Currants

Currants (Ribes spp.) are related to gooseberries. In addition to the black currant there is also the red, pink, white and Asian currant; all are different species.

As you may suspect, currants are not a tropical plant.  According to the USDA map zones, they are best adapted for zones 3-5 where temperatures may get down to minus 40 degrees Fahrenheit (-17 Celsius). Two states where currants are commercially grown are New York and Michigan.  In addition, they require between 800 and 1600 hours below 45 degrees Fahrenheit (7 Celsius) during the winter in order to complete their chilling requirement and begin spring growth. 

Some currants are being successfully grown in the coolest parts of the San Francisco Bay Area and in coastal Northern California.  It is questionable whether they will do well in Southern California or in Hawaii.  On the Big Island of Hawaii, it is possible that they could grow at high elevations, but there is no confirmation yet.

Currants are deciduous shrubs, at least on the Mainland, growing about 5 feet tall and wide. They like morning sun and since the leaves readily sunburn and are susceptible to wilt at high temperatures, some shade in the afternoon is preferred. Placing 2-3 inches of mulch around the planting is desired.

Currants can withstand ocean winds, but the salt air will burn the leaves. Shrubs must be pruned annually to increase yields and rejuvenate plants. Birds feeding on ripening fruit along with the powdery mildew fungus are potential primary problems.

Currants are easily propagated by hardwood cuttings of one year old wood; rooting hormone will help.  Softwood cuttings also root easily.

Black currants are truly a nutritious food. They are rich in many phytonutrients, antioxidants, vitamins, essential fatty acids and minerals. They have twice the potassium of bananas, four times the vitamin C of oranges, and twice the antioxidants of blueberries. Black currants contain anthocyanins, potent antioxidants which are responsible for the color of the fruit.  They are known to reduce inflammation and the effects of arthritis in the body, similar to aspirin.

Note: Black currants and all currants are unrelated to the small raisins sold commercially as dried or black currants. These raisins are made from the black Corinth grape, a small grape shipped for centuries from the Greek port of that name.

For those wanting to try currants in Hawaii, an Internet search will yield several nurseries that sell young plants. Two are Miller Nursery - and Hidden Springs Nursery