Plant Profile- Lima Bean

Wandering around my old abandoned gardens today I spotted a lima bean with a decent crop of pods splitting in the sun. The dry weather has the good effect of improving the quality of the seeds as moisture can lead to mould. I bundled them up in my shirt, and shelled them on the verandah. Until I lucked onto lima bean I was starting to wonder if I would find any staple legumes that liked my local conditions. Long ago I had even been ambitious enough to try lentils and chickpeas. These plants are from much cooler and drier locations. They grew reasonably well but the pods failed to form (lentils) or rotted (chickpeas). Kidney beans have been very hit and miss and seem to have issues with our local mineral balance. They do OK when I add plenty of lime (or use mushroom compost) but fail on goat manure (could be too salty). They also suffer from bean fly making timing the crop tricky.

Originally I wasn’t planning to grow lima bean. I had seen the Madagascar bean form in permaculture circles and heard tales of how rampant the vines were, leading me to assume that the beans themselves were pretty low on the edible scale. Legume seeds contain all sorts of interesting toxins that can be removed or inactivated by various combinations of soaking, sprouting, cooking and fermentation. Chickpeas are at the lower end of natural toxicity, then lentils, then kidney beans and finally soy beans that are risky to eat in large amounts unless thoroughly fermented. My dear Dad was responsible for getting the seeds, and I planted them in an old abandoned vegetable garden at the base of a piece of metal concrete rebar mesh that I used as a trellis. Its growth lived up to its reputation, and when it produced a heavy crop of seeds I decided to hold my nose and try cooking them. I soaked them for 12 hours with a few changes of water, then boiled them while removing the scum that formed, and finished by pressure cooking. To my surprise they were delicious and we added them to our various stews for a few months with no digestive issues.

Lima beans are a rare example of a crop that was domesticated twice, independently in the lowland and highlands of South America. Normally the first domesticated variety spreads out so quickly that it prevents wild forms in other places being domesticated later. The lowland forms are less diverse, represented by the large seeded Madagascar bean. The highland forms are more variable and include butter beans commonly bought in a can.

The crop has large seeds that germinate readily from direct sowing in spring and flowers through autumn, with pods drying through our reliably dry winter. They seem to be immune to our local seed sucking bugs that destroy my pigeon pea. Even better the plants are perennial so will produce for a few years, though I noticed my original plant produced less this year, possibly due to no extra nutrient being added to its bed. The first year the single plant in a 2.5 m long bed produced about 4 kg of dry beans.

It is interesting to weigh up the return on investment of the crop. It was never watered, weeded, sprayed or netted. The initial fertility in the old bed might be worth an hours work at most (it already had other crops through it after whatever fertility was added). Harvest of last year’s big crop probably took about an hour all up, and processing and cooking about an hour each as well, a couple hours more if I needed to gather fire wood. Lima beans have about 12 500 kJ of energy per kilogram dry, or 50 000 kJ total. Humans need about 10 000 kJ a day in energy, so eating nothing but lima beans this harvest would last about five days, based of about 6 hours’ worth of invested time (round up to about one days’ worth of activity). This estimate seems right since staple crops optimised for energy production yield closer to 10 for return on investment. A legume also produces useful amounts of protein but diverts the plants resources away from making starch. Lima beans have the benefit of being quite easy to store and even leaving them in open containers with minimal effort drying them saw no mould or storage pests appear.

The interesting part comes when you consider the trellis the plant was growing on. This piece of rebar cost maybe $40, but the energy behind it is more relevant. The total weight is about 30 kg, and iron manufacturing consumes about 20 megaJoules, or 20 000 kJ per kilogram, so a total of 600 000 kJ of energy in the form of mostly coal and oil was used to create the rebar. This ignores the energy needed to transport it. For context this means the trellis alone consumed 12 times more energy in its construction than the crop produced during the first year. You could also imagine it would take twelve years of crops to break even energetically (though comparing coal energy to food energy directly is pretty silly). At any rate the rebar is already rusting heavily and will probably be unusable in a couple more years at most.

Luckily rebar trellises aren’t the only way to grow lima beans. I tried a new smaller seeded form last year and grew it on a bamboo trellis. This was the first one I made, hammering in the upright poles with a post banger, and tying horizontal slats in place with left over baling twine. It lasted a couple of years before starting to fall over but did a good job. Using the baling twine was bothering me though, for strategic reasons since cheap plastic string may not be around forever, and for practical reasons since it meant I needed to carefully pull the trellis apart afterwards to extract the plastic from the crumbling bamboo. The trellises I made this year used a different trick, splitting the bamboo posts with a bamboo hatchet after they had been hammered in, then using the three upright slats to weave the horizontal slats into place, no string required. This construction is a little weaker but has held up well so far. I estimate constructing the bamboo trellis on the 2.5 m bed scale above would take about 1 hour, dropping the return on investment a little lower.

Even more luckily for me my new found passion for lima beans collided with making a wonderful new friend who has been growing heritage lima bean strains in the district for many years. She generously shared her seeds with me and they will be going through test plantings soon this spring. Among them are a few bush varieties that require no trellising and thus save on the time and hassle of building trellises, though they make harvesting a bit more unpleasant if you don’t like leaning over or crouching. Down the track I might be able to find a way to grow climbing lima beans up other support plants as well to avoid that job. Having multiple strains also opens the door to cross pollinating different varieties to produce even more genetic diversity to suit our local conditions.

This little thought experiment about the rebar and lima beans is a useful illustration of the enormous influence fossil fuel dependent resources have on our lives, and offer an insight into why they transformed the planet and human society so dramatically in the last few hundred years. They wont last forever and when they are gone those of us left will need to find ways to live without them.

My old Madagascar bean on the rusting rebar trellis.
Bamboo trellis mark 1 with string, starting to disintegrate
Bamboo trellis mark 2 with split and woven uprights and no string.
A useful harvest of Madagascar beans, destined for the pressure cooker.

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