Sunday, November 15, 2015

Sandalwood Trees in Hawaii

Sandalwood trees (Santalum sp.) are classified as hemi-parasites. The term describes a plant that is green and can produce its own food but also derives water and some nutrients by attaching to the roots of other plants. This process can effectively join together whole plant communities through their root systems. The plants that donate nutrients to sandalwood are called hosts; sandalwood trees do not grow well without a host. In fact, this ‘inter-cropping’ is not only possible but necessary. 

According to the publication, Species Profiles for Pacific Island Agroforestry, S. ellipticum, one of four species known as Hawaiian sandalwood, can “… successfully develop into relatively large individuals when growing with endemic species such as Wikstroemia sandwicensis (‘ākia) and a fan palm Pritchardia remota (loulu) in windward, lowland areas. In more xeric (dry) environments it has developed successfully in association with the endemic shrub Chenopodium oahuense (‘āheahea) and Chamaesyce hypericifolia. Apparently S. ellipticum, is flexible in the species it can parasitize for needed nutrients.”
Santalum ellipticum is endemic to the Hawaiian Islands. It is found as a sprawling to bushy shrub near the ocean shore. It is occasionally found as a larger shrub to small tree in dry gulches, on slopes, and frequently in rocky habitats. S. ellipticum is adapted to arid habitats with typical summer drought in leeward lowland locations.
Hawaiian sandalwood species generally resist most insect attack; sometimes infestations of whitefly or scale insects can be found. Insecticidal soap may be used to treat such infestations. Slugs and snails will also feed on newly sprouted plants. The trees generally tolerate a broad range of soil conditions but show a preference for well drained neutral to slightly alkaline soils.  Since many Hawaiian soils tend to be acidic, an application of lime would be appropriate to bring the soil closer to neutral. The wood of the sandalwood trees is often used for carving handicrafts, art, musical instruments and decorative furniture.  

Tuesday, November 3, 2015

Avocados and Clay Soils Don't Mix

Avocado trees, planted in a clay soil in an area of high rainfall, will frequently be unhealthy. Various species of trees can tolerate ‘wet feet’ such as the great magnolias of the South which grow in the swamps. Other trees, like avocado and citrus, do not like to sit in water. In order for most trees to thrive in places of high rainfall, they must either be able to tolerate lots of water or be grown in well-drained soils. Unfortunately, a clay soil does not facilitate good drainage.

A key element to remember is that roots need oxygen as much as they need water. When it rains, water fills the air pockets in the soil. For good plant health, a portion of that water needs to quickly drain away to allow the air to come back. In clay soils this does not happen; the clay holds onto the water.  

In arid climates, farmers who have clay soils simply apply water less often. In tropical climates, the clay soil has little or no chance to dry out; oxygen is excluded, and the roots die. In the case of avocados, it has been shown that after 72 hours in a water logged soil, their roots begin to decline.  Once this happens, leaves turn yellow and drop resulting in twig and small branch dieback.

Clay and rain are a bad combination for many plants. There is not much to be done for existing trees; the soil can’t be changed neither can the rain be stopped. A good recommendation is to plant on a slope where there is better drainage. Sometimes trees can be planted on mounds about 3 feet high. It won’t do any good to dig a hole, put the tree in and fill the hole with a different type of soil. That is like putting sand in a bathtub, plugging the drain and planting a tree in it.