What you need to know about growing pomegranates in your garden

In a seminal 2010 study on the potential benefits of pomegranates in the prevention of breast cancer, the following conclusion was reached: “Pomegranate intake may be a viable strategy for the chemoprevention of breast cancer.” Specifically, pomegranate consumption inhibits the activity of aromatase, the enzyme that produces estrogen and its associated breast cancer cells, especially in post-menopausal women.

The conclusion of another 2009 peer-reviewed article about nutrition and cancer that addressed the cancer-prevention potential of pomegranates was more far-reaching: “Recent research has shown that pomegranate extracts selectively inhibit the growth of breast, prostate, colon and lung cancer cells in culture. In preclinical animal studies, oral consumption of pomegranate extract inhibited growth of lung, skin, colon and prostate tumors.”

The pomegranate is native to the Middle East. It is one of five fruits (along with grape, fig, olive, and date) indigenous to the Land of Israel that are mentioned in the Bible. Thus its ability to survive drought is embedded in its DNA, as years of drought in the Middle East are as common as they are in California.

Yet just because a plant species can survive a drought does not mean it will thrive with a minimum of irrigation following a dry winter. Where pomegranates are concerned, for example, the same water regime for growing citrus trees is recommended. That means a pomegranate tree should be deep soaked every 10 to 20 days during the summer, depending on how hot it gets. You can do this by moving a slowly trickling hose around the drip line or canopy circumference line, where water drips off foliage when it rains.

Where pomegranates are concerned, a little fertilizer goes a long way and no more than a half-pound of actual nitrogen should be applied to a mature tree. Late January would be the best time to do this because February often is our wettest month, and rain would soak the fertilizer into the plant’s root zone.

How is a half-pound of actual nitrogen calculated? Let’s say you have a bag of fertilizer that is 16% nitrogen. (The three numbers on a bag of fertilizer, separated by dashes are, from left to right, the percentages of nitrogen, potassium, and potassium in the bag). For every 100 pounds of this fertilizer product, 16 pounds are actual nitrogen. Thus 1/2 pound of actual nitrogen would equal around 3 pounds of the product in this bag.

However, if you were regularly applying compost and mulch to the soil surface, the half-pound of actual nitrogen you need would be released to the plant naturally through these layered materials and no supplemental fertilization would be required.

In an email, Margie Loya recently asked: “Why is it that my pomegranate tree had its normal blossoms, but then they fell off and only a few pomegranates were produced?”

The botany of the pomegranate (Punica granatum) helps to explain the phenomenon of flower drop. On the pomegranate tree, both male and hermaphrodite or perfect flowers are produced; 60-70% of them are males on some varieties.

It should be noted that nearly all the flowers you see on plants are perfect, meaning they have both male and female organs. Some plants have separate male and female flowers, either on the same plant (corn, squash, cucumber, melon, and walnut trees, for example) or on different plants (pistachio and date palm, for example).

The preponderance of male pomegranate flowers means you are going to see lots of flower drop since only flowers which turn into fruits (the hermaphrodites) stay on the plant. However, in order for a flower to produce a fruit, it must be pollinated; so where conditions for pollination are not optimal, unpollinated hermaphrodite flowers are going to drop as well.

The problem here is that the stigma (female part) on the pomegranate flower is only receptive to the male pollen for two to three days. If bee activity – pollen is carried on some of the three million hairs on a bee’s body to waiting stigmas — is curtailed due to environmental conditions, pollination and fruit development will be reduced.

It is thought that adverse environmental conditions can also affect the number of hermaphrodite flowers and thus the number of fruits that develop in a given year. Our current drought, for example, could have reduced the number of hermaphrodite flowers and therefore the potential number of fruits on your tree. Even when flowers are abundant on our fruit trees, pollination will depend on the trees’ being well-hydrated and not water-stressed. That is why keeping the soil moisture level steady is important. Fluctuating soil moisture will not only affect pollination but the phenomenon of fruit splitting – whether in pomegranates, citrus, or tomatoes. In this context, it is especially important to keep pomegranate trees well-watered when their fruits are ripening because, unlike tomatoes and citrus, pomegranates have a natural tendency to split while still attached to the stem.

Pollinate your pomegranate tree by hand to enhance fruit production. Take a small artist’s paintbrush and dab it on the yellow pollen grains that appear soon after pomegranate flowers open. Then transfer the pollen to stigmas. In a hermaphrodite flower on a pomegranate tree, dozens of pollen-bearing anthers surround a single stigma that protrudes above the anthers.

Hand pollination is especially important where dwarf pomegranates are concerned. As Nancy Carr who gardens in Lake Forest emailed: “I planted a dwarf pomegranate tree about a year ago. It was full of flowers that fell off! What causes that?” Some dwarf pomegranate trees — which grow no more than six feet tall as opposed to the 20- to 30-foot height reached by conventional pomegranate trees — appear to be completely dependent on our help when it comes to giving fruit and will only do so where hand pollination is employed. The small fruits, while edible, are not sweet and their principal attribute is ornamental since they stay on the tree for many months.

Margie Loya also asked: “How long do you leave bulbs in the refrigerator?”

Most of the bulbs we plant do not require refrigeration. Tulips and giant hyacinths require it, as do many daffodils and crocuses, and keeping them refrigerated for eight weeks is advised. Make sure they are not in the same drawer as fruits and vegetables since some of them give off ethylene (when ripening) which would damage the bulbs. My recommendation is to plant the following seven bulbs that do not require refrigeration and come back year after year in the garden, spreading happily with nothing more than benign neglect required on our part: paperwhite Narcissus, Crocosmia, Nerine, Hippeastrum, Crinum, naked lady (Amaryllis belladonna), and snowbells (Leucojum). Leucojum is a real charmer, whose nodding white, campanulate flowers are tipped in green and mildly fragrant. Leucojum spreads like wildfire in the shade. Search these bulbs on the Internet to find mail-order vendors who supply them.

John Krakowski asked, “What specific tomato varieties will be best for fall planting?” The safest bet are cherry tomatoes These will bear fruit throughout fall and even winter as long as we don’t get a serious freeze. Here is a list of some tomato varieties that do well when planted at this time: cherry – Sun Gold, Red Robin, Sweet 100; heirloom – Brandywine, Nepal, Garden Peach; hybrid – Celebrity, Early Girl, Jetsetter.

Tip of the Week: If you are seeking a California native that blooms this time of year in some shade, consider scarlet coyote mint (Monardella macrantha ‘Marian Sampson’), whose foliage is delicately fragrant when rubbed.

I discovered it thanks to the excellent assistance of Neda Rivka at the Theodore Payne Foundation in Sun Valley. She directed me to two other plants that I took home for shady spots. One of them is a maidenhair fern (Adiantum capillus-veneris ‘Banksianum’) and the other a sword fern (Polystichum munitum).

Both ferns would make excellent indoor plants, keeping in mind that species that appreciate shade in the garden typically need a bright light exposure when taken indoors.

I asked Rivka for her best recommendations for California natives that bloom in the fall and she cited two: Baja fairy duster (Calliandra californica) and California fuchsia (Epilobium canum). The former shows off tassel lampshade red blooms while the latter is covered with narrow fiery orange tubular flowers. Both attract hummingbirds.