Monday, December 29, 2014

Cotton in Hawaii

In Hawaii, the cotton plant, Gossypium tomentosum, is a perennial shrub lasting about 3-5 years, depending on growing conditions. In Hawaiian, it is called Ma’o. This plant can be found growing in coastal plains and dry forests primarily on the leeward sides of the main Hawaiian Islands. Ma'o naturally grows in hot, dry, windy coastal areas tolerating the salty spray. Conversely, the plant does not do well in locations with continuous high rainfall and in waterlogged soil.

Periodic pruning is necessary to control the height, to keep the shrub full and to prevent low lying branches from spreading.

In 1838, a commercial cotton industry was actually started in Kailua on the Big Island of Hawaii. Although it lasted for about a century, cotton never became an important trade item. Even though early Hawaiians stuffed pillows with the fibers, the cotton was not used as a fabric. 

 For more information on Ma’o, see the website for native plants in Hawaii at 
and refer to the UH CTAHR publication entitled, “Ma’o (Hawaiian Cotton). 

Photos by Forest and Kim Starr

Monday, December 15, 2014

Hapuu, the Hawaiian Tree Fern, vs. the Australian Tree Fern

The Hawaiian tree fern is native to most of the Hawaiian Islands. Although once common, hapu’u stands have been reduced due to a large number of ferns being harvested for orchid media and landscape use. The last remaining large stands of native hapu’u are found on the Big Island.

The Hawaiian hapu’u  are very slow growing; the young ones grow at about 3.5 inches per year while the older plants grow even more slowly, eventually growing to  15-20 feet tall.  The unfurled fronds are covered with silky, red-brown wool-like fibers called pulu.  In the past, pulu was used for stuffing pillows and mattresses and for dressing wounds.

The Hawaiian tree ferns are relatively easy to grow. They grow best in well drained slightly acid soils and partial shade; they will tolerate full sun in cloudy upland areas. They need a steady supply of water and occasional light applications of a complete, slow release fertilizer. Old and injured fronds should be pruned. It is illegal to ship tree ferns or products from the ferns internationally. 

 The Australian tree fern, Cyathea cooperi, is considered invasive in the State of Hawaii due to aggressively out competing native plants in the forest understory. As a threat to  Hawaiian forests, this fern eventually displaces the native ferns, including the slower growing Hawaiian tree fern, or hapu’u.  

Although invasive, the Australian tree fern is being sold in Hawaii at many commercial plant nurseries. This fern grows to 40 feet tall and tolerates full sun in cool wet areas. The spores are spread by wind and can travel over 7 miles from the parent plant.

 The best diagnostic characteristic to distinguish between the Australian tree fern and the native hapu'u is the hairs on the leaf stems. With the  hapu’u, the hairs are either fine and reddish-brown for hapu'u pulu (Cibotium glaucum) or fine and black for hapu'u i'i (C. menziesii). The hairs on the Australian tree fern are broad and white.

                                                Cibotium menziessi

  Photos: Native Plants Hawaii, University of Hawaii


Monday, December 8, 2014

Propagation of Blueberries

Blueberries are propagated from either softwood or hardwood cuttings.  

Hardwood cuttings are collected in late January or February, after sufficient chilling has occurred. Follow these simple directions: collect shoots from the previous summer, 12 to 36 inches in length. Select healthy material, avoid propagating from plants that have odd-looking or stunted foliage. Divide the shoots into pieces 5 to 6 inches long, removing any flower buds. Place cuttings in a propagation bed at a depth of one-half to two-thirds of their length. Finally, keep moist.

Softwood cuttings are taken in late spring from the current season's growth, 4 to 5 inches long. Here are the directions: collect these cuttings when the stems have developed woody tissue but are still somewhat flexible. Remove all leaves with the exception of two or three terminal leaves.  Place cuttings in the propagation bed, under mist at a depth of one-half to two-thirds of their length.

Rooted cuttings are eventually transplanted into pots and held for about one year.  During the time of rooting, keep beds moist while being aware not to over water.
For the propagation process, a greenhouse is not necessary, but some type of propagation bed/chamber, under 40 to 70 percent shade with a mist system is recommended; an area as small as 3x3x3 can be used.
The mist system should keep the media uniformly moist but not soggy.  An intermittent-mist system with frequent, short misting intervals is recommended in order to keep the humidity near 100 percent.  However, keeping the cuttings at this constant moisture also creates an ideal environment for pathogenic fungi to grow. Thus cleanliness is very important; use new or sterilized planting mix and pots, keeping them raised off the ground.
Potting media containing various mixtures of coarse sand, ground pine bark, perlite, sawdust, and peat moss have proven satisfactory. According to a publication from the University of Hawaii, a good rooting medium recipe is a mixtures of coarse sand, ground pine bark, and peat moss at 1:1:1, or perlite and peat moss at 1:1.

Monday, December 1, 2014


Are your plants foaming at the leaves?

A white frothy substance on plants may be a spittlebug. Inside all that froth is a tiny bug about ¼ - ½ inch long.  The immature stage of this insect sucks the plant juices just as aphids do. But in the process, spittlebugs remove so much water and carbohydrates, that excess fluid is produced. They then cover themselves with this fluid. The spittle is produced when the insect bubbles air from the tip of the abdomen into the liquid. This is an ingenious method to protect themselves from predators and  from drying out.

Although the removal the plant fluids can weaken the plant, rarely are spittlebugs a serious problem. Simply spraying a strong stream of water can physically remove the pest. A soap/oil spray can also be used.

In addition to basil, the spittlebug attacks other common plants such as rosemary, mint, hibiscus and some pine trees.

Monday, November 24, 2014

Avocados with Black Strings

Why are some avocados stringy?

The strings in the fruit are vascular tissue, part of the conductive system of the plant bringing water and nutrients to the fruit.  They are always in the fruit but are unnoticeable in high quality fruit. From non-grafted trees, or seedlings where a genetic mix takes place, fruit can exhibit darkened, thicker strands as a natural characteristic, especially as it reaches maturity and beyond.  

These strands are usually the same color as the fruit pulp but can discolor or blacken for various other reasons. The most common reason is cold temperatures. This is true in avocado growing in areas like California where temperatures can reach freezing or below. Cold weather, however, would not apply to fruit growing in tropical regions such as the Hawaiian Islands. 

The blackened vascular tissue can also be caused by a disease. There are a number of fungi which enter an avocado at the stem end of the fruit.  Some of these pathogens will cause vascular discoloring as a precursor to decaying the flesh. 

These stem-end rotting fungi are present in the soil and on dead plant tissue and assist in the breakdown of organic matter. The spores of the fungi spread by wind and splashing water. This disorder is clearly made worse in a rainy environment. Infection typically occurs when the fruit is still on the tree, but it does not develop until after the fruit is picked due to anti-fungal compounds present in unripe fruit. Fruit will continue to decay as it ripens.

Control Measures For this Fungal Disorder 
  • Clean out dead limbs and twigs which helps to reduce the incidences of fruit rot.  
  •  Keep trees healthy with proper nutrients and water.
  • Maintain a thick layer of mulch under the tree’s canopy which will help to minimize the disease.   
  • Place avocados in the refrigerator after picking them, if not eaten soon. Caution: Temperatures below 41 degrees Fahrenheit can cause fruit injury in some varieties.
  •  Spray trees with a copper fungicide to limit infection if the problem is severe.

Monday, November 17, 2014

Hummingbirds and Pollination


About 25% of plants are wind pollinated. The rest rely on pollinators: bees, bats, beetles, butterflies and yes, hummingbirds, as well as some other birds. During the day hummingbirds feed about every 10 minutes and consume up to 2/3 of their body weight from the nectar of plants; they can service 20 flowers per minute. The wings of hummingbirds beat up to 55 beats per second and allow these tiny birds to fly at speeds up to 50 mph. They can hover and even fly backwards or upside down. 

Hummingbirds are primarily attracted to tubular flowers. They are stimulated by color, especially the color red. Clumps of bright red, orange and pink flowers are more visible to them than other colors. Plants with red, tubular shaped flowers are an excellent choice in the garden to attract hummingbirds. Other plants that attract these birds are gladiolus, honeysuckle, iris, lupine, nasturtium, petunia, and cosmos. 

Lastly, I was asked if hummingbirds pollinate vegetables. I am having difficulty finding specific vegetables that they pollinate. That’s probably because there are not many vegetables with red, tubular shaped flowers, which attract the hummingbirds.  

Photo: University of Maine