Greenhouse- Papayas

Papayas from Colorado? ¡Si como no! We  investigated yield potential of two varieties of papayas under Colorado greenhouse conditions. Papayas are of interest as a crop due to its sweet taste, health benefits (packed with nutrients, antioxidants, and used medicinally for indigestion), and use in hair and skin products. Regional and national demand is relatively high and growing.

Previous research at Colorado State University involved growing papaya in the Arkansas River valley. Researchers were able to produce green fruits which can be eaten or processed.

Papayas growing on tree trunk

Photo courtesy of www.AlohaSeeds.com

METHODS:

We planted 72 seeds (acquired from Aloha Seeds, Hawaii) of each of the two varieties of Chinese dwarf papayas (Red Lady #786 and Tainung #1) into Winstrip 72-cell trays on January 1, 2004. We used Sunshine No. 3 soil mixed with 10% worm castings and topped the seeds with vermiculite. We kept the trays misted but not too wet.

Red Lady #786 papaya variety Tainung #1 papaya variety
Red Lady #786
Tainung #1
Photos courtesy of www.AlohaSeeds.com
Seeds began germinating on January 20, 2004 . The seeds in the cells on the perimeter of the tray germinated first indicating soil warmth is a factor.
Closeup of papaya seedlings Germinating papaya seedlings

Germinating papaya seedlings
Approximately 15 of the seedlings seemed to had a virus, the roots were healthy but the plant wilted and died. The remaining seedlings (33 Tainung and 35 Red Lady) were transplanted into 3-gallon pots into a mixture of coir and perlite on March 12, 2004. We began fertilizing the seedlings with ammonium sulfate (20-0-0) and then switched to Peters 15-5-15 Cal-Mg to keep the pH from going to low (optimum pH for papayas is between 6.5 to 7.0). Note that the papayas are not being grown organically.
Red Lady papaya plant
The papayas began blooming mid-summer, 2004. Unfortunately many of the flowers were dropping, probably due to insufficient nutrients and/or water. We switched from fertilizing once a week to a constant feed and watered more frequently. The papaya plants produced hermaphroditic and female flowers. As of November 2004, the female flowers began producing fruits. Fruits can be grown without pollination but will be smaller. The hermaphroditic plants are self-pollinating, as the stigma grows through the developed stamens. Those plants began producing fruits in March of 2005.
Hermaphroditic Papaya Flower Female Papaya Flower
Hermaphroditic Flower
Female Flower
On December 3, 2004, all papaya plants were moved into a newly renovated quonset greenhouse with a heated floor wherein warm water runs through tubing under a pea gravel floor. The papayas thrived with the bottom heat. Minimum night temperatures were set to 55 degrees F (below that the fruits and flowers abort) and the maximum ambient temperature in the day was 85 degrees F. An irrigation system was also set up with individual watering rings for each plant.
Papaya Fruits
Papayas in the quonset greenhouse
Irrigation system
A few insect pests affected the papayas. Two-spotted spider mites were troublesome, as well as aphids. Fungus gnats were also a problem. We introduced Hypoaspis miles (predatory mites) to the soil to control the fungus gnats and Feltiella acarisuga (also a predatory mite) to control the two-spotted spider mite. Lacewings were introduced unsuccessfully (they didn’t lay eggs as we had hoped), and so we resorted to introducing adult ladybird beetles which dropped the aphid population quickly.

Growth of the papaya plants is recorded below (see Table 1). The plants grew quickly after we increased the fertilizer rate in the spring of 2005. Stem girth was measured near the base of the plant at the soil. Height was measured from soil level to the top of the upper leaves. We transplanted the plants into 7- gallon pots in April of 2005.

Ladybird beetle release for aphid control
Table 1.
12/3/04
3/5/05
3/13/06
Variety
avg. height (cm)
avg. girth (cm)
avg. height (cm)
avg. girth (cm)
avg. height (cm)
avg. girth (cm)
Tainung
100
3.7
156
7.4
192
7.6
Red Lady
66
3.5
125
5.8
130
6.7
Table 2. Yield data from 7/22/05 to 9/30/05
Variety
# fruit/plant
lbs./plant
lbs./fruit
Tainung
1.77
0.89
0.5
Red Lady
3.76
2.33
0.62
We picked the first ripening fruit on July 22, 2005. Red Lady appeared to give higher yields on a shorter plant. We believe that the overall yields from our study were somewhat low and the first fruiting was late due to fluctuations in our fertilization rates and frequency.
Taste Testing
Red Lady Papayas

It was determined that with adequate light, heat, and fertilization, papayas can indeed be grown in greenhouses in Colorado, however the commercialization of papaya as a greenhouse crop is unlikely due to the slow rate of maturation and high cost of heating in the winter.

 

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