Many gardeners still wait for tangerines to turn orange before picking.

With this method, waiting for more orange coloring, the fruit might be past ripe and characterized by dry fruit segments. Coloration can be an indicator for ripeness in California and Arizona.

But here and in other tropical areas, color is not a good guide for harvesting. Large temperature differences, such as 85 degrees in the day and 45 at night, are the mechanism which produces the orange coloration. In contrast, temperatures in the tropics do not vary drastically; thus, fruit tends to stay partially green.

If you know the variety, you can find out when the harvest period is. If you don’t know the type of tree you have, then when the fruit first begins to show color, pick one and taste. If it’s not ready, wait a week or two and pick another one.

Eventually, you’ll discover the right time and know the approximate picking time for next year.

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For those interested in planting deciduous fruit trees, January and February are the time to purchase them.

Hawaii, along with other tropical areas, is of course, not ideal for growing deciduous fruit trees. I would not recommend a commercial venture, but a tree or two in the backyard could produce some nice fruit for the family, especially at higher elevations.

Deciduous fruit trees are those trees that lose their leaves and go dormant in the winter — apple, peach, nectarine, plum, almond and cherry. They need cold in order to produce an abundance of good quality fruit.

Through the years, however, breeders developed deciduous fruit trees with a low chilling requirement; these are the varieties that will do best in Hawaii. In general, though, the trees will have low yields, smaller fruit and, at times, scant foliage.

The higher elevations will obviously produce the better trees. When shopping for a deciduous fruit tree, select only the low chill varieties, apples and peaches are the most common.

Deciduous fruit trees are rated by their chilling requirement, that is, how many hours they need below 45 degrees in order to adequately break dormancy and produce a good, consistent crop of fruit. Many trees need 500 to 1,000 hours below 45 degrees. But the low chilling varieties require only 100 to 250 hours. These are the varieties that have a chance to bare fruit in Hawaii even though some areas on the Island will receive zero hours below 45 degrees.

Apple trees along with other deciduous fruit trees can be purchased about January and February at Paradise Plants Home and Garden Center in Hilo. Call (808) 935-4043.

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I am growing a number of passionfruit vines (lilikoi) and I am curious to know how long they will live? I have heard they will die after three years.

The passionfruit vine, or lilikoi, as it is known on the Islands, is a relatively short lived plant. Some vines might produce for only three to four years, while others can last a decade. They will generally not die outright, but rather yields begin to decline.

Commercial growers should keep harvest records and when yields begin to drop, it’s time to replant. Backyard growers don’t have to be so quick to pull the plants since they can usually tolerate less fruit.

I have a vine reaching the decade point and is producing quite well. Since I don’t keep records though, I can’t tell if my yields are down; certainly not substantially.

Commercial strawberry growers have a similar situation. In the southern U.S., plants remain in the ground for three or four years. After each season, yields decline as the population of pathogenic organisms, such as nematodes and a variety of fungi, increase and attack the roots. In contrast, California strawberry growers remove the plants, fumigate the soil and replant each year. Because of this practice, yields remain high each year.

Hilo resident Nick Sakovich is a professor emeritus of the University of California. He has worked in the field of agriculture for 30 years. Email your questions to Sakovich at askthegardenguy@earthlink.net.