Earthly Delights is an eight-acre organic farm in South Kona where Bonnie and Bacci Perata have employed as many sustainable practices as possible during their nearly twenty years on the farm. They are dedicated to composting and mulching as well as growing some of their own fertility to limit their off-site inputs. Growing nitrogen fixing plants is an excellent way to add nutrition to the soil in small gardens as well as on farms.
On a recent visit to the Perata’s farm, I asked for a tour of their nitrogen-fixing plants to gather some information that I could pass on to other gardeners and farmers. They gladly took me on a wild ride through their farm with many stops and lots of explanations.
Crotalaria, perennial peanut, gliricidia and other plants in the Fabaceae (Legume) family including pigeon pea trees and all kinds of bean plants can be grown to fix nitrogen. They can serve as temporary cover crops or grown as perennials to add fertility to the soil as well as offering cuttings to be used as mulch. They all collect nitrogen from the air and sequester it in their roots, offering fertility for themselves as well as plants growing near them.
Bonnie began by telling me how they fed the soil on their farm when they first arrived. She and her husband Bacci seeded the areas they had cleared with crotalaria, sometimes known as sunn hemp. Crotalaria juncea is a tropical plant in the Legume (Bean) family. It can grow tall and produce yellow flowers that, once pollinated, become seed pods with lots of seeds for future plantings.
The Peratas waited a few months until their first crotalaria crop matured at about three feet tall. Then they mowed it and re-seeded. The second crop grew to nearly six feet tall at maturity. The taller plants were nourished by the nitrogen released into the soil by the first planting. Their third planting grew over nine feet tall. They mowed again leaving lots of crotalaria mulch. By then they knew their soil had been sufficiently enriched to help their food crops thrive.
Crotalaria seeds are available online. It is easy to grow from seed and can provide a good nitrogen source when grown and cut prior to planting edible or ornamentals. Crotalaria cuttings can provide nutritious mulch and the roots that are left in the ground will continue to release nitrogen. This plant has the added advantage of discouraging root knot nematodes. See https://www.ctahr.hawaii.edu/oc/freepubs/pdf/RES-036.pdf for more information on sunn hemp.
Once they started planting edible crops, Bonnie and Bacci added more nitrogen fixing plants to the farm. They planted some large Legume family trees that are now well over fifty feet tall with root systems that spread in all directions.
They also planted the attractive ground cover, perennial peanut. They continue to grow Arachis pintoi, sometimes known as ‘Golden Glory’, at the base of larger plants where it serves as a living mulch and adds nitrogen to the soil.
Once established, perennial peanut offers a low growing mat of green leaves and yellow flowers that shades out most weeds and helps reduce soil erosion. It produces seeds to regenerate itself while continuing to feed the soil. It can also be propagated vegetatively from cuttings or stolons.
Planting perennial peanut at the base of larger shrubs and trees offers numerous benefits. For more information on perennial peanut go to the UH CTAHR publication: https://www.ctahr.hawaii.edu/oc/freepubs/pdf/OF-23.pdf.
The Peratas also planted gliricidia on the whole farm. Their initial strategy was to put in one plant about every seven trees in the orchards so their roots would touch the roots of the orchard trees around them. Though gliricidia can be grown as a tall shrub or tree, Bonnie showed me that they have kept most of them pruned low. They coppice it so they can use the chipped branches as mulch while leaving the rooted plant in place to store the nitrogen it collects from the air. This is then slowly released into the soil in their coffee and cacao orchards.
Native to parts of Central and South America Gliricidia sepium can also be cultivated as an ornamental plant with lots of lovely lavender flowers. Known as ‘madre de cacao’, it is often used as a shade tree for cacao, coffee or tea plants. Though gliricidia seeds are available online, it will grow easily from cuttings.
The large trees that the Peratas planted early on are now quite large. Both the ice cream bean (Inga edulis) and the monkey pod (Samanea saman) continue to serve as nitrogen fixers. These trees may be too large for small gardens but can offer many benefits on a large piece of property.
The ice cream bean tree produces pods that are about a foot long and contain lima-sized beans surrounded by a sweet, cottony pulp. The fluffy pulp tastes similar to vanilla ice cream, hence its name.
Huge monkey pod trees have seed pods that are filled with a sticky, sweet pulp. Both the pulp and the seeds are edible, and have a licorice-like flavor. The name stems from their attraction to monkeys in their native South America. There, monkeys gather in the trees to eat the sweet seed pods. Monkey pod trees add nitrogen to the soil through their roots as well as other parts of the plant. Its leaves, blossoms and seed pods fall on the ground, producing additional nitrogen-rich material.
Another nitrogen fixing plant to consider growing is the pigeon pea tree. Known botanically as Cajanus cajan.This small, short-lived tree also produces pods of edible peas following the bloom if its yellow-orange flowers. The peas that have a nutty flavor are called gandules in Spanish and recipes using them abound in cookbooks and online.
Pigeon pea trees also offer a ten-to-twenty-foot overstory of light shade for lettuces and cole crops like kales and cabbages. This multi-level planting can offer beneficial growing conditions as well as additional fertility for the lower story plants.
Growing nitrogen fixing plants is an excellent way to add nutrition to the soil in small gardens as well as on larger properties and farms. I have used several of these plants in my own small garden plots to add soil fertility before planting ornamental or edible plants. Since most plants in the Bean family serve as nitrogen fixers, you might want to follow the Perata’s example and try growing a few to add fertility to you soil.
Gardening Events
Saturdays:
•“Work Day at Amy Greenwell Garden” from 9 a.m. to 12:30 p.m. Meet at the Garden Visitor
Center across from the Manago Hotel in Captain Cook. Come with a mask and prepared to practice social distancing. Volunteers cn help with garden maintenance and are invited to bring a brown bag lunch. Water and snacks provided. Visit the website www.amygreenwell.garden/get-involved/volunteer-1/ and sign up for the weekly email for more information on work days.
Wednesday, May 24:
•“Dealing with Coffee Leaf Rust Organically” from 2 to 5 p.m. at Mahina Mele Farm in Honaunau. If you plan to attend contact colemel2@gmail.com for more information.
Save the date:
June 15 – 17:
• “Hawaii Coffee Association’s 2023 Annual Conference &Cupping Competition.” A live event at the Kauai Beach Resort &Spa. For more information go to https://www.hawaiicoffeeassoc.org/Events.
Farmer Direct Markets
(check websites for the latest hours and online markets)
Wednesday:
•“Ho’oulu Farmers Market” 9 a.m. to 2 p.m. at Sheraton Kona Resort &Spa at Keauhou Bay.
Saturday:
•“Keauhou Farmers Market” 8 a.m. to noon at Keauhou Shopping Center. Information on their online market: keauhoufarmersmarket.com/onlinemarket
•“Kamuela Farmer’s Market” 7:30 a.m. to noon at Pukalani Stables
•“Waimea Town Market” 7:30 a.m. to noon at the Parker School in central Waimea
•“Waimea Homestead Farmers Market” from 7:30 a.m. to noon at the Waimea middle and elementary school playground
Sunday:
•“Pure Kona Green Market” 9 a.m. – 2 p.m. at Amy Greenwell Garden in Captain Cook
•“Hamakua Harvest” 9 a.m. to 2 p.m. at Hwy 19 and Mamane Street in Honoka’a
Plant Advice Lines
Anytime: konamg@hawaii.edu
Tuesdays &Thursdays: 9 a.m. to noon at UH-CES in Kainaliu – 322-4893 or walk in
Diana Duff is a plant adviser, educator and consultant living part time in Kailua-Kona.