Over the past few months, Napa County Master Gardeners have been conducting a field trial of two types of shelling beans. We wanted to find out which of the two would perform better in our county’s varied microclimates. The plants needed to mature before the rains arrived so that we could harvest the dry beans. Well, we almost made it.

Napa County has four main climate zones, as defined by Sunset’s Western Garden Book. Carneros and American Canyon fall in Zone 17, where marine effects make for cool summer temperatures in the 60- 75 degree Fahrenheit range. In this zone, the growing season lasts from May to early December.  

Zone 15 includes the area around Mt. Veeder, Spring Mountain and Howell Mountain. This zone is described as “cool coastal,” with frequent afternoon summer wind and a growing season from May to November. 

The valley floor is considered Zone 14, or coastal warm, with some marine air moderating the heat. The growing season can begin early, in mid-March, and last until mid-November.  

Finally, the foothills of Pope Valley and Lake Berryessa belong to Zone 7, characterized by hot summers and a growing season from May to mid-October. Cool fall temperatures arrive early in Zone 7.

Our field testers began the project with heirloom bean seeds from Rancho Gordo, the Napa store. We selected two varieties: ‘Tepary’ and ‘Christmas Lima.’ Tepary is a small golden bean, about the size of a lentil. Christmas limas are large, kidney-shaped beans with a colorful cream and burgundy skin. We  selected these two types because they vary in the number of days from transplanting to harvest, although they require the same growing conditions.

Beans are a warm-season crop. They need a soil temperature of at least 65 degrees to sprout, and they grow best when temperatures are in the seventies and eighties. Our 25 team members reside in all four climate zones. They planted their seeds between June 15 and June 30.  

Some gardeners sowed their seeds directly in the ground, bypassing the transplanting process. In most gardens, the seeds sprouted readily in five to eight days and grew steadily after that. Those who started seeds in containers transplanted the seedlings when they had their first true leaves. A few gardeners had poor germination and replanted near the end of June.  

If you want to plant shelling beans next summer, here are a few pointers:

Avoid planting beans in beds where you grew beans or peas the previous year. Bacteria that inhibit growth can accumulate in the bed. 

Beans grow best in full sun and prefer fertile, well-drained soil. Plant them one inch deep, two to six inches apart, and in rows 12 to 14 inches apart. For large beans, allow more space between them. Plants need to be far enough apart to allow for air circulation to prevent disease. This is particularly important for dried beans since they stay on the vine a long time.  

Provide one inch of water every seven to ten days. Regular watering is critical during flowering and pod growth. Beans do not typically need much fertilizer.  

Christmas limas are pole beans. Stake them when they start to vine. They can reach seven to eight feet in height, depending on their support. In contrast, Tepary beans are bush types that do not require staking for good production, although they don’t object to it.  

Pods form about two weeks after flowering. When blooming ends, stop watering. This alerts the pods that it is time to begin drying out.

Potential bean pests include birds, cutworms, beetles, aphids, spider mites and whiteflies. In our Napa Valley trial gardens, aphids were a recurrent problem that most gardeners controlled with a vigorous water spray, although the spray did disturb some blossoms and pods. Insecticidal soap is an alternative; be sure to spray the underside of the leaves as well as the top. For more pest management information, visit the Master Gardeners during office hours (see below) and inquire about University of California publications on integrated pest management.

When green beans appear, pick them frequently to ensure continued production. For dried beans, leave the pods on the plant until they begin to dry out. When the pods are at least half yellow, it’s time to harvest them. Both types of shelling beans need to dry completely before shelling.  

Uproot bush beans and place them, dirt and all, on an old sheet. Put them where they will have good air circulation and low humidity. When they are completely dry, put the pods in an old pillowcase and bang them around to loosen the beans from the pods.  

Our trial team is harvesting Christmas limas now. Some gardeners simply cut the plant at ground level, leaving the vine to dry. Then they harvested the individual brown pods and spread them out to dry thoroughly. These shrunken pods may not look like they have viable beans inside but they do.  When they have dried sufficiently, the beans can be easily removed from the pod by hand. 

The Master Gardeners participating in the bean trials harvested just under a pound of dried Tepary beans for each 20 plants. Initial data for the Christmas limas suggest about a pound per 10 plants. This is a satisfactory yield, and we are pleased with our trial.  

We concluded that both the Tepary bean and the Christmas lima can thrive in Napa County, with only moderate attention and care. Whether planted in Calistoga, Carneros, East Napa or on the valley floor, these two varieties performed well. 

Unlike fresh beans, the dried beans store well. When you have eaten or processed all the tomatoes, zucchini, cucumbers and figs you can manage, try Rancho Gordo’s recipe for Tepary Bean Dip. People tell me it rocks.

Napa County Master Gardeners (http://cenapa.ucdavis.edu) answer gardening questions  Monday, Wednesday and Friday, 9 a.m. to noon, at the UC Cooperative Extension office, 1710 Soscol Ave., Suite 4, Napa, 253-4221, or 877 279-3065.

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