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  

Friday, November 9, 2012

Growing Persimmons in Hawaii


Persimmon trees (Diospyros kaki) can successfully be grown in Hawaii. They grow well in areas above 500 feet and are raised commercially above 2000 ft.  Occasionally they are found at low elevation.

Common varieties are Hachiya and Fuyu. The Hachiya variety is heart shaped and pointed at the apex. The accumulation of tannins cause the fruit to be astringent which produces a puckering if eaten before it is fully soft and ripe. Persimmons can be picked firm and ripened at room temperature. The astringency will be eliminated during the ripening process, leaving a creamy texture and tangy-sweet flavor. Hachiyas, along with the variety Maru, are often dried.  The Fuyu fruit is flatter and eaten when firm and crisp; it is non-astringent.

Persimmons are one of the few trees that will tolerate a heavy clay soil as long as drainage is not severely impeded. Few insect pests attack persimmons. The oriental and Mediterranean fruit flies occasionally damage fruit.

On a health note: one study conducted in Japan showed that the peel of the persimmon contains phytochemicals known as proanthocyanidins which may protect cells against oxidative damage associated with aging. In another study which compared apples with persimmons, researchers found that persimmons contain significantly higher concentrations of compounds instrumental in fighting atherosclerosis, a leading cause of heart disease, heart attacks and stroke. In traditional Chinese medicine, it is a remedy for hiccups. The persimmon is native to China and was introduced to Japan.