Pretty much what the title says. We just bought a house in the fall that has a lovely huge tree in the back yard. The tree produces about five bazillion cubic feet of long pods in the autumn, blanketing our yard in a thick coating pierced only by dropped twigs from the tree. The twigs are coated in six-inch-long flesh-seeking envenomed thorns, but that’s neither here nor there.
Coincidentally, we’re getting ready to start a compost pile for kitchen scraps, and we need “browns” to balance the “greens” from the kitchen and from mowing the yard (browns=high-carbon plant matter; greens=high-nitrogen plant matter). I looked at the tonnage of locust pods, and thought, Hey! We should compost these!
But then I thought about a couple of issues:
They have a pretty low surface-area-to-volume ratio, especially compared to suggested browns like hay and leaves.
Legumes are usually pretty high-nitrogen, which might unbalance the compost.
Legumes are also often pretty high-fat, making them harder to break down in compost.
If we try composting them and it doesn’t work, we won’t really know for sure for six months or more.
Does anyone have any ideas about this admittedly bizarre question?
Being leguminous, robinia is likely to produce nitrogen nodules on the roots, in the soil. The common misconception is that nitrogen is locked in the pods of legumes. Bean or pea pods would have more ‘green’ value than the pods of a robinia.
Pods from the Black Locust or Robinia pseudoacacia are ‘brown’ or contain a high amount of carbon compared to nitrogen. Therefore these will help to balance against the higher nitrogen levels, the ‘greens’, in the kitchen scraps.
You will undoubtedly have a surplus of robinia pods unless you have a very, very large family.
If you cold compost these the seeds will pass right through and be still viable when the composting is finished; much of the fibrous material of the pods will persist helping soil structure in soils it is applied to.
I suggest a well planned hot composting, research the subject, fertilise the heap, keep moisture to the optimum 55% and when done you will have a compost so nutritious that you could sprinkle on you cereal or even grow babies in it.
By the way a garden compost heap should initially have a C:N ratio of about 30:1 dropping to 10:1 when complete. If you were to compost sawdust, a C:N ratio of 80:1 would be the starting point, dropping to 50:1 at completion. This is due to the high cellulose and lignin content which are very difficult to compost.
Considering this, you may need to aim at a C:N ratio somewhere in between the two, maybe 50:1.
Wow–thanks, guiness! I have a couple follow-up questions, if you’re still there:
You say that I’d probably have a surplus of pods. Does this mean that the pods are edible? I know they smelled pretty tasty last autumn, but didn’t try eating the pulp inside them.
I’m guessing I don’t need to worry too much about the beans sprouting in the garden, since they ought to be pretty easy to weed out. Is that a deadly misconception?
You recommend hot composting, but I’m a little leery of it: our first garden is likely to be teeny (probably less than 50 square feet of actual beds), and I’m just not sure whether we’ll have enough stuff to do a proper hot-compost pile. If we go for cold-composting, do you think we’re likely to crash and burn? Note that this’ll be the first time I’ve done anything like a real compost pile before; previous attempts have been little more than little middens in the backyard on which we throw fruit rinds and leaves.
Thanks, though, for the fantastic overview of the issues!
Daniel
Invest in a chipper and shred them before composting (you can put twiggy garden stuff through it too; increasing ythe surface area in this way makes a huge difference to the rate of composting.
You can shred a years woth of stuff in about seven minutes. If you have the right kind of relationship with friends, family, or neighbors you can share a chipper. Kind of a commie idea, I know. But It can work out pretty good. I hear southerners are pretty neighborly.
Peace,
mangeorge
Aren’t chippers pretty expensive? Our gardening book suggested getting one if you had a big operation. Maybe I can rent one. Or maybe the sweet lady across the street, the one that offered to let me borrow her wheelbarrow earlier today, has a chipper I can borrow.
Hmm…if I get a chipper, though, that might take care of the tremendous pile of befanged locust branches pruned from the tree and dumped in a corner of the back yard just before we moved in…hmm…
I’ll check out the compost forums tomorrow. Thanks! (And if anyone knows whether locust pods are edible, lemme know – half a dozen sites on black locusts don’t mention anything about uses for the pods or even whether they’re deadly poison).
I don’t believe the pods are edible, Left Hand of Dorkness. I always raked mine, but the few that escaped the rake would last until spring, unmolested by our busy troupe of squirrels.
Depends what you mean by ‘chipper’ - there are small, affordable electric garden shredders that will handle quite a throughput of waste. I have one of these and it really does make a difference - all of the prunings from the garden go in there and the shredded result rots down in 12 months, whereas simply piled up, it would remain a pile of twigs for maybe five years or more.
The action of shredding on woody waste does more than just increase the surface area, it allows the material to pack down a little more (not too much though, you don’t want that), meaning that moisture can wick up into it - a pile of springy twigs never really stays damp on the inside.
Well, I just checked prices, and the cheapest one I could find to purchase was $400 – more than we’ve got to blow on our compost pile at this point. However there’s a place in town that I can rent a small one from for only $35 a day; this may be my best bet, although I doubt it’ll be able to put a dent in the massive branchpile in the yard. May have to send the big pile out for the landfill and save the mulcher for the pods exclusively.
Too bad they’re inedible – I saw you’d responded, mangetout, and expected to come in to the thread to say, “Well, of course YOU can eat them!”
1)No i just meant an excess of woody material to successfully compost all the pods, kitchen scraps or green value may be the limiting factor.
2)They should be fine to weed out. The problem with Robinias is suckering from the roots not huge amounts of seed (the seed needs to be scarified in order to germinate)
true, you need more bulk to hot compost. Slow composting will just take more time and not kill any seeds or pathogens.
As an alternative to a chipper, use a lawn/mulcher mower to cut them up. No extra outlay.
