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Master Gardener Journal  


A   B O U N T I F U L   G A R D E N



Papaya: A Tantalizing Taste of the Tropics

by Dick Gross, Master Gardener

Botanical Name: Carica papaya Linnaeus

Family: Caricaceae

Technically, the papaya is not a tree but an herbaceous succulent. Succulent plants that possess self-supporting stems (such as the papaya and banana) are known as herbs.

Papayas grow best in tropical and subtropical climates, where annual temperatures stay between 70 and 80 degrees Fahrenheit and annual rainfall is well over 40 inches. The papaya is a relatively short-lived plant in even the most favorable environment, and rarely exceeds 4 years here in the Salt River Basin where its demise is almost always caused by root rot. Still, papayas can be grown successfully here in the desert, where 7 inches of annual rainfall are common and temperatures range from 32 to 120 degrees. One just needs to practice careful irrigation and know how to cope with an occasional frost.

A papaya plant blooms continuously throughout its adult life. A seedling 8 inches tall planted in Phoenix about the first of March will typically grow to a height of 4 to 5 feet by the first of May, with blossoms forming in the leaf axils (that upper space between the leaf and stem). By October it can exceed 7 or 8 feet, and have mature fruit if germination has occurred.

COLD WEATHER PROTECTION
A typical cold snap in Phoenix and the surrounding valley is generally of short duration, occurring between 5:00 am and 7:00 am. I've lived on the West Side for 29 years, and I've experienced one low of 15 degrees Fahrenheit, and several in the range of 29 to 32 degrees.

Brief lows in those ranges are not enough to hurt a relatively dry root system, so don't worry about protection. A sustained low of 33 to 34 degrees, however, will damage foliage. The leaves and crown (growing tip) are quite sensitive, and a mild frost will kill them. The stem of the papaya plant is frost-tender, but I have never seen one damaged by frost.

There is one important thing to keep in mind where frost protection is concerned: NEVER FLOOD THE TREE BASIN, as is often advised for the protection of citrus. The soggy soil will cause root rot, and the tree may be dead before the ground dries.

If frost protection becomes necessary, you can wrap the plant with burlap or blankets. Commercial frost covers are available, but they don't offer enough protection for a long exposure. If a prolonged frost is predicted, you can drive a stake under the cover several inches from the stem and attach a 25-watt light bulb using an extension cord. (Make sure the bulb has a safety shield, and remember that electrical devices should never be used in wet weather). For trees over 13 feet tall, you can try mounting a 100-watt flood lamp or an infrared light under the tree canopy and forget about using frost cover (unless you can handle yourself on 6-foot stilts).

One effective way to protect foliage is to aim an air fan into the leaf mass. Use the highest-output shop fan you can find. This will protect your papaya in all but a severe freeze of long duration, and even then the fan will minimize frost damage. If you are blessed with several papaya plants or other tender subtropical fruit trees, get several fans.

If you should end up losing all the foliage and growing tip to frost damage or crown rot, don't despair. A healthy root system kept dry in cold weather will force branching, and each branch will have the potential to bear fruit. Some cultures behead their papayas on purpose to increase production.

IRRIGATION
Growers have observed that the papaya will handle all the water you can give it. That is true only during the summer, where drainage is ideal and soil temperature is above 70 degrees Fahrenheit. Root rot is certain to set in whenever the soil is cold and damp for more than a few days at a time, and it is always fatal.

There isn't much you can do about extended rain, except to plant on a slight mound to direct water away from the root zone. Since the leaves form a natural umbrella that deflects rain toward the drip line, you can cover the area beneath the tree with plastic when rain is anticipated. But be sure to remove it when the sun comes out again. Once wet, shallow cultivation, using care to avoid wounding roots near the surface at the stem, can help aerate and dry out the soil.

In the months of November through February, when ambient air temperatures are in the 40s and soil temperature is below 60 degrees, papaya growth is very slow-virtually at a standstill. The method of irrigation at this time is critical. Water modestly only at the drip line and only when the soil there is dry to a depth of one inch. Once established, the papaya has a much greater tolerance to drought than to cold, wet feet.

For winter irrigation dig a 3-inch-deep trench the width and shape of a garden spade around the tree, like the imprint of a doughnut, with the inner ring directly beneath the drip line. The trench itself should lie outside the drip line. As the plant grows, extend the trench outward to keep up with it. Check ground moisture by scratching an inch or so into the soil. If completely dry, fill the trench with a garden hose at the rate of about a half-gallon per minute. When full, stop. Don't water again until you scratch the soil and find it quite dry.

The papaya will take full Arizona sun. If the soil temperature is above 55 degrees and drains well (the basin will empty in less than 30 minutes), it is okay to flood irrigate. The tree will respond with very rapid growth. When the temperature rises over 90, use good judgment but water often and deeply.

FERTILIZATION
The requirements are not well established in this area. I have raised more than 20 plants to maturity, some with erratic fertilizing and others with no fertilizer, just water. If there was a difference, I failed to detect it then. Having learned, however, that papayas do indeed respond to nitrogen, I presently feed as follows:

With seedlings until transplanted into 1-gallon containers, use 1/4 teaspoon per gallon of water-soluble fertilizer with every watering.

With plants in 1-gallon containers, drench already-moist soil every 2 weeks with about 1 quart of water mixed at the rate of 1 tablespoon per gallon of 20-20-20. Any commercially available soluble fertilizer is okay. I've found slow-release plant food to be satisfactory and easiest to apply.

For established plants in the ground, salt about a cup of ammonium sulfate monthly (or 1/4 cup weekly) around the drip line. Rake it in lightly and water well. CRFG Fruit Facts recommends 1/4 pound of 21-0-0 monthly, increasing to 1/2 pound per month after the plant is established. Do not add fertilizer to cold, wet soil.

VARIETIES
The Mexican papaya appears to be easily grown in the Phoenix area. The fruit-at least that with which I am familiar-is the size of small watermelons. I have not tried to grow it because I don't like the taste. Grocery store papayas are generally a Hawaiian-grown Solo variety. The common cultivars of the Solo are Sunrise, Sunset, Vista, Waimanolo and X-77 (Kaymia). These vary in disease resistance, size, shape, color of the fruit, and size of the tree. None of these varietal differences are of any particular value to the recreational home grower in the Phoenix area.

POLLINATION
Your tree may be male, female or hermaphroditic. You won't know until it blooms. Even then it may take some conjecture until the fruit actually sets.

There is no mistaking the male. It has clusters of small white blossoms borne on branched tentacles that may be more than 18 inches long.

The female has a slightly larger single white blossom borne on the head of a miniature fruit close to the stem in a leaf axil. The petals tend to be straight. If the fruit shrivels after the bloom dies, it has not been pollinated.

The hermaphrodite, difficult for the inexperienced to distinguish from the female, has all the necessary sexual paraphernalia in its blossoms to develop fruit. The white petals on this flower have a slight right-hand twist that is easier to observe while the blossom is still closed. It is best to plant several seeds or seedlings to improve the odds for getting the sex you want. They can be thinned out later.

PLANTING THE SEED
Scoop the seed from the papaya. The seeds are encased in a gelatinous envelope. I find it best to break it apart and wash the seeds thoroughly and then air-dry. I usually soak the seeds overnight, and then mix them (they may number up to 400) with a handful of peat moss. Spread the mix evenly over a tray containing 3-4 inches of a good planting mix. Cover that with 1/2 inch of the same mix. Cover with plastic wrap until they break the surface, keeping the medium damp but not wet. Sprouting can take from 15 days to 6 weeks or longer for some inexplicable reason. Bottom heat always helps. As soon as the sprouts break the surface, start getting them into bright light to harden them off. Insufficient light will make them leggy. Prick the seedlings out when they are about 2 inches tall and transplant into 4-inch containers in a potting soil that drains well. You will lose a few to damping off, but don't let that concern you. You will have planted a hundred seeds, and you only need 2 or 3 trees. Don't plant in the ground until the soil temperature is at least 55 degrees Fahrenheit-70 degrees is even better.

Resources: Internet sources for this material include CRFG Fruit Facts, the University of Hawaii, Texas A & M, and the University of Florida, with input from members of the Arizona Rare Fruit Growers. In large part, the information is based upon my own experience. I am still learning, still experimenting. What I believe today to be the facts may turn out to be fallacy tomorrow.

Photography: Dick Gross


Maricopa County Master Gardener Volunteer Information
Last Updated July 28, 2003
Author: Lucy K. Bradley, Extension Agent Urban Horticulture, University of Arizona Cooperative Extension, Maricopa County
© 1997 The University of Arizona, College of Agriculture and Life Sciences, Cooperative Extension in Maricopa County
Comments to Maricopa-hort@ag.arizona.edu 4341 E. Broadway Road, Phoenix, AZ 85040,
Voice: (602) 470-8086 ext. 301, Fax (602) 470-8092