Dry, Flavorless Citrus?

Overly mature fruit is a major cause of dryness in citrus. In other words, if the fruit is left on the tree too long, drying occurs.  A few other reasons include:  1) the application of too much nitrogen.   2)  At times, dryness may occur when a tree is young; the fruit will improve as the tree ages.    3) Trees budded on certain vigorous rootstocks will make the problem of dry fruit worse. 4) For citrus grown in temperate climates, dry fruit is the result of low, freezing temperatures.   Overall, certain varieties of citrus, especially mandarins, seem to be more susceptible to producing dry fruit.  In Hawaii and other tropical areas, a further complication is the fact that citrus fruit does not color well. In other climates, such as California, fruit develops a deep orange color due to the great differences between day time and night time temperatures.  And under these conditions, oranges may actually turn color before they are sweet enough to pick.  In the tropics, however, where there are less temperature fluctuations, the orange coloration does not develop well and therefore is not a good indication of ripeness. In fact, fruit is often sweet but will still show a green coloration; by the time the fruit shows good color, it may have dry segments already forming.  If you don’t know the harvest season for your particular fruit, I would suggest picking one good sized fruit, even though it may still be greenish in color.  If it is not sweet enough, pick one every 1-3 weeks until it tastes sweet. Fruit will develop more sugar the longer it is held on the tree.

Sweetness in Citrus Fruit or Lack of It!

Warm sunny days: The accumulation of heat units is most important in determining the sugar content in citrus. Simply put, citrus fruits become sweeter the longer they remain on the tree up to a point. If the fruit seems ready to pick, but the taste is not sweet enough, then leaving it on the tree a little longer should sweeten it.   

Location, location, location: In certain places, fruit from a given tree will simply not produce enough sugars. Of the hundreds of citrus varieties, not all are adapted to a specific area. For a given region, some varieties won’t produce good quality fruit!

The rootstock factor -  There are numerous citrus rootstocks. They impart a variety of characteristics to the fruit. Some rootstocks will enable the tree to produce an abundance of fruit, but with poor quality, in this case, low sugar content. For commercial growers, choosing the right rootstock is an important factor when selecting new trees for an orchard. Homeowners on the other hand, have few choices in rootstocks when purchasing a tree.


  Will citrus fruit get sweeter by adding potassium or lime to the soil?

The notion of adding potassium or lime to sweeten citrus fruit has been around for a long time, but it has not been substantiated by scientific research. Fruit from trees deficient in potassium are small and thin-skinned, yet they can be juicy and have a good acid and sugar content. Adding potassium to deficient trees will increase the size of the fruit. This has also been noted in other fruit trees, such as apples and peaches.  An excess of potassium makes fruit large with coarse rinds, thick skins and poor eating quality.

 A classic chart taken from the University of California’s Citrus Industry Volume II, shows that as the percent of potassium in the leaf rises, there is a slight decrease in the sugar content of the juice in the fruit.  The vitamin C, however, content increases.

If soils are truly potassium deficient, by all means apply potassium. This being said, sweeter fruit will not be a result of adding potassium.

In regards to lime (calcium carbonate), an old study (1958) in South Africa, on calcium deficient orange trees, noted that the fruit was acidic and low in sugars. The trees were stunted, chlorotic (yellow), sparsely foliated and exhibited profuse blooming and excessive young fruit drop. If the soil is truly calcium deficient, adding lime may increase the sugar content of the fruit. A soil analysis can determine whether the soil is deficient in calcium, as well as other nutrients. Contact a local university cooperative extension to inquire about where an analysis is available.

The Beautiful Vireya

Vireya are part of the rhododendron family, classified as a subgenus. They are native to Southeastern Asia - New Guinea, Borneo, Sumatra and the Philippines, growing quite often in the cooler mountainous areas. On the Big Island of Hawaii, vireya, also called tropical rhododendrons, are successfully grown from Volcano down to the coast.  There are about 300 species of vireya. Azaleas are part of this group.

Vireya grow well in the sun.  Yet locations of intense sunlight along with high afternoon temperatures should be avoided. In this case filtered sun is best. On the other hand, planting vireya in the shade will produce leggy shrubs with inferior flower production. No hot summer sun, no heavy shade.

It is important to plant vireya in soils and potting mixes that have excellent drainage. In addition to growing them in the soil, and sometimes in cracks and crevices, they can also be found growing as epiphytes. An epiphyte is a plant that grows upon another plant such as a tree, but is not a parasite on that tree.  The epiphyte derives its moisture and nutrients from the air and rain and sometimes from debris accumulating around it.

Vireya are well adapted for growing in pots and may even grow well indoors in a well-lit room. They come in a variety of beautiful, vibrant colors such as salmon, pinks, orange and yellows.

For those interested in learning more about vireya, join the Hawaii Chapter of the American Rhododendron Society or search to see if there is a chapter in your area.

Japanese Maple in the Tropics

Being a deciduous tree, the Japanese maple is indeed adapted for cold climates. Hawaii, as well as other tropical locations, does not provide the best growing environment; yet the trees will grow in these areas. I have one Japanese maple that is now 9 years old. Admittedly, it is not the most vigorous tree, and I think it is continually looking for winter. Sometimes it goes dormant in spring or even in the middle of summer, but it still grows. A question might be, how many years can it survive without experiencing a dormant period?

There are over 1000 cultivars of Japanese maple. Obviously some will adapt to tropical regions better than others. Usually, nurseries select those varieties best suited for their area.

Regardless of the climate, another problem is an insect called Chinese rose beetle. This beetle makes holes in the leaves weakening the tree. 

In the evening, when beetles are feeding, placing a cover or netting over the small trees will exclude the pest. Another choice for control is to use a systemic insecticide with the active ingredient imidacloprid. Granules can be applied to the pots and watered in. 

On this website, gardenguyhawaii.com I have a detailed report on this pest; search Chinese rose beetle in the space on the left of the screen.

Trouble with Palms

"The bottom fronds of our triangle palm started to die, and then suddenly the whole palm fell over," a friend complained.

A significant pest of Pritchardia palms is the banana moth, Opogona sacchari. The triangle palm is also attacked by this moth. It seems that the female moth targets wounded or stressed palm tissue to lay her eggs. Stresses can include drought, flooding, mechanical wounding, poor nutrition, and herbicide injury. The larvae generally feed on decaying and dead plant tissue but will feed on living tissue, too, causing extensive damage. In affected palms, larval tunneling, along with the characteristic frass (insect droppings), can often be seen. Fully developed caterpillars measure just over an inch. The adults have greyish brown wings are 3/8 to 5/8 inches long.

The main treatment is prevention: keep palms growing well; give them adequate fertilizer, and supplemental water during a drought. Gardeners also need to be careful with the weed wacker! Female moths are looking for wounds to lay their eggs. Bt (Bacillus thuringiensis), an organic insecticide, can be applied to these wounds, as well as those caused during pruning.

For more information about this pest see the CTAHR Cooperative Extension Service publication, “Banana Moth – A Potentially Fatal Pest of Pritchardia and Other Palms”, by Scot Nelson and Mark Wright.  CTAHR stands for the College of Tropical Agriculture and Human Resources at the University of Hawaii. 

Ohia Trees (Metrosideros sp)

There are four distinct species of ohia tree that are endemic to Hawaii. In addition to genetic differences, environmental factors will cause physical variations in the trees. Elevation, rain, and temperature all have an effect upon these trees. 

In general, the shapes of leaves from trees growing in hot, dry deserts are often small in order to conserve water loss through the leaf. Contrast this to the large-leafed plants of the tropics. Ohias occur in a wide range of habitats, from just above sea level to 8,200 feet: from dry forests with less than 16 in annual rainfall to wet forests with more than 33 feet of annual rainfall. This along with its genetic propensity for variation will produce trees of diverse appearance. The species name, polymorpha which actually means many forms has eight varieties. Thus tree height and form, leaf shape and flower color are highly variable.

Concerning the care, ohia trees can be damaged and even killed from a lack of water. During periods of drought especially, supplemental watering will be needed. Trees growing in the pahoehoe lava (exhibiting a smooth, billowy, ropy surface) may do well when young and water requirements are low. Nevertheless, as trees increase in size, if adequate water is not supplied, they can dry out and even die.  Mulch will help, but of course, not piled against the trunk.

Since ohias are adapted to grow in low nutrient soils, beware of over-fertilizing. Slow-release fertilizers or natural compost is best. 

Start a Garden

Here are some fundamental points to help along the way: 

·      Plant only as large a garden as you can easily maintain. Don’t over plant and become overwhelmed with the many garden chores: weeding, planting, pest control, soil preparation. 

·      Choose recommended varieties for your region. Midwest and Eastern US seed catalogs, with pictures of giant tomatoes are fine, but those varieties are not necessarily adapted for a tropical climate. University of Hawaii CTAHR seed program develops and sells vegetable seeds suitable for the Hawaiian Islands.  http://www.ctahr.hawaii.edu/seed/

·      Consider locating the garden within easy walking distance to your house in order to carry tools there and eventually return with baskets of produce. 

·      Select a site that receives at least 8 hours of full sun each day.  Plant vegetables where they are not shaded by trees, walls or fences. Nearby trees and shrubs with roots reaching into the garden will compete with the vegetables for water and nutrients.

·      For those with minimal space, grow crops that produce the maximum amount of food for the area available.  You can harvest a lot of radishes, onions, lettuce, bok choy and tomatoes in a small plot.  Plants like pineapple, watermelon and pumpkin squash take up lots of space for what is harvested.  In addition, consider planting vegetables that can be grown vertically instead of horizontally. Vining crops such as tomatoes, squash, cucumbers and pole beans can be trellised or staked to minimize ground space and increase garden productivity.

·      Plant perennial vegetables such as rhubarb and asparagus to one side of the garden so they are not disturbed as you prepare the ground for subsequent annual crops.

·      And finally, try succession planting. A crop like indeterminate tomatoes can be harvested over a long period of time; one planting will last for many months. With other crops like corn, beets and lettuce, the entire crop will mature at approximately the same time. Unless you want to eat all your corn in a short period of time, stagger the plantings at 2-3 week intervals, or more. Read more about growing vegetables by clicking on the column on the right.

When Are Pineapples Ripe?

The following information is applicable to pineapple varieties presently available in the marketplace, yellow or white.

Select a pineapple that is plump and fresh-looking. The leaves in the crown should be crisp and green with the body of the pineapple firm. A larger fruit won’t necessarily be better tasting or riper than a smaller one.

According to Maui Land and Pineapple Company, pineapples, unlike bananas, do not ripen after harvest. They may advance in shell color, but they do not get any sweeter; they actually begin to degrade. A pineapple on a shelf in the market is as ripe as it’s going to be.  In terms of sweetness, color is not an indication.  Often times, depending upon the weather, green fruit will be sweeter than yellow fruit.  The only true indication is the size and flatness of the 'eyes' of the fruit. Typically, the bigger the eyes and the flatter the eyes, the sweeter the pineapple will be.

The color of the outer shell of the pineapple is not necessarily a sign of maturity or ripeness: a pineapple’s flesh can be ripe, sweet, and ready to eat when the shell is still quite green. A University of Florida publication states, “For optimum fruit sweetness, pineapple fruit should be harvested when 1/3 to 2/3 or more of the peel color has turned from green to yellow.”  

Other indicators are as follows: a good, ripe fruit has a dull, solid sound; immaturity and poor quality are indicated by a hollow thud. If the pineapple is at its peak freshness, it will have a sweet and fragrant odor. If the odor coming from the pineapple smells too sweet and almost alcoholic, it is past its peak. If you don't plan to use your fresh pineapple right away, store it in the refrigerator, where it will keep longer. Generally, once it is ripe, fruit may be held in the refrigerator for up to a week. In addition, the ease of pulling leaves from the crown is not a sign of ripeness.

 Many years ago scientists classified fruits into two categories: climacteric and non-climacteric.  Climacteric fruit usually undergo dramatic changes during ripening. These changes have often been associated with a surge in respiration and ethylene production. Ethylene is a natural plant hormone.

The avocado, apple, melon and banana are classified as climacteric fruits whereas the pineapple is classified as a non-climacteric fruit.

 Non-climacteric fruit (oranges, pineapple, grape, watermelon) do not exhibit the increase in respiration or the rise in ethylene production. In addition, they normally do not undergo dramatic changes such as softening after harvest.