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Fava Bean Cover Crops in Seattle

September 22, 2008

Yes, yes…I keep posting about getting out and doing crop exchanges. And, yes, here I am writing that I’m going to get out there today to do it. Sometimes life gets in the way of what we intend, but if I don’t get out there soon, I’m going to miss my window to get in my cover crops! And if anything is going to help my Seattle garden, these cover crops are it!

Fava Germination: Day 1

Fava Germination: Day 1

About a week ago, I found an old packet of fava bean cover crop seed in the garage. Fava’s have fairly fat seeds, which mean often they can store longer than the “packed for” date on the bag. A basic rule is “the bigger the seed, the longer the shelf life”. We may not notice it, but seeds are alive, using up minute bits of stored energy as they wait in packets, on rocks, in tree crevaces, in sidewalk cracks, etc…for the moment to germinate. Eventually, they can use everything up and have zero chance of germinating. But, in many cases these little DNA packets are surprising. Seeds from archeological digs have occassionally proven viable; sometimes not. Because seeds can often be viable beyond their “expiration date”, I will often pre-germinate them before putting them in the ground. This is what I did about a week ago with my favas. Buying a new packet would be just another expense I’d rather avoid.

Germinated Favas: Day 8

Germinated Favas: Day 8

In addition to showing us if our seeds are viable, pre-soaking to germinate can also speed up the process. The consistent moisture and the warmth of being on a morning-sun window sill not far from a furnace vent ensures them an optimal environment in which to break from their skins and start growing. They won’t survive long in this environment, but its a good way to get started. So, here I am about a week later with little less than 100% germination rate. (No, I didn’t do a scientific count. I just eye-balled it.) Some seeds didn’t open and grew mildew instead. Others are beyond putting out that first root and are showing hints of dicot leaves ready to emerge. So, if I don’t get them in the ground, they’re going to poop out soon.

Those first emerging leaves are the early food-factories of the plants. The stored seed energy is starting to run out for these little guys, and they need to get into the soil and sunshine in order to establish themselves and expand those factories. So, today’s the day.
So, how do I get the seeds going?
Well, it’s pretty easy. I grab a small, shallow dish or pan. In this case, I used an old toaster oven cookie sheet that is just about as wide as my window sills. I folded a papertowel to double thickness, wetted it, and sprinkled a single layer of favas over it. Then, I folded a second paper towel, wetted it and placed it gently over the beans. I placed the pan of beans on a window sill that gets dappled morning light (aka, it doesn’t cook the beans). Each morning and evening, I checked to be sure the towels stayed damp, rewetting as needed. As some seeds mildewed, I removed them to reduce the chance of spreading the problem to viable seedlings. Within a week, I have my tiny seedlings.

Why do I grow favas?

Well, favas have that amazing ability to fix nitrogen. So what does “fix” mean. Seriously, what’s wrong with nitrogen that it needs to be fixed anyway? Well, nitrogen comes in several forms. To explain it simply: plants can use nitrogen in some of its forms; plants cannot use nitrogen in other forms. And, yes, plants need nitrogen. Again, simply: nitrogen is a nutrient that plants use for green growth. And, remember, the green growth is what makes up their little food factories!

So, if I grow a plant like fava (or clover or other beans or several other nitrogen fixers), the plants do the work of correcting my soil so that it is nitrogen-rich in forms that next year’s plants will be able to use. As well, they do this in a way that does not disturb microbial and other insect life. (If I add a bunch of chemical fertilizers I can end up messing with the flora-fauna ecosystem in ways that are more difficult to repair.)

Too, as the favas grow, they produce green leaves and stems, which are nitrogen-rich. Next spring, I’ll cut the tops off the plants and cut the tops into the garden beds. These fresh cuttings will serve as food for the microbial life. The nitrogen in the cuttings won’t be immediately in the form that my new plants will want, but it will be a food source for soil microbia. As the soil microbia eat and excrete this food source, their digestive process will convert this additional nitrogen source to a form that my new plants will want. All the while, the roots of the plants will still be in the ground fixing more nitrogen!

Eventually, I will cut the entire plant, roots and all into the beds, which by now should be filled with positive soil microbia and rich with plant nutrients and fixed-nitrogen. And, my spring vegie beds will be thrilled to meet that soil. As I plant up the vegies, I usually add snow peas, green beans and other plants that will continue the nitrogen fixing work throughout the growing season. So, in addition to rotating my crops, I will continue to experiment with building symbiotic plant relationships year-round.

This year the favas are particularly going into two place. First, I’ll be putting these sprouts among this year’s corn patch. Corn depletes the soil rapidly, so I want the favas in there to rebuild as quickly as possible. Second, one my oldest raised beds is significantly depleted of nitrogen. I have lettuce growing in it now for winter, and it is my best covered bed. So, I’m hoping that the favas and lettuce can live together all winter, feeding me and feeding the soil.

Yes, I’m going, I’m going…the plate of seedlings is just to my left. I’ll be putting them in the garden within the next 20 minutes!

For more information on Fava Beans as cover crops, visit the OSU website.

Later that day…yes, the fava beans are in the ground as are my remaining lettuce starts and chard starts. Before I put in the bean starts, I pulled everything out (except a few lettuce and a pepper that’s just ripening and oh-so-cute), and I cut in about 4 gallons of worm-bin compost. Hopefully the microbials and the nutrients will also help rebuild my sad bed. As well, I pulled a soil sample before I changed the soil. I’ll run tests later to set a baseline for where the beds are now. This may help as I re-evalute it in the months ahead.

Mixed Harvest at Fall Clean up

Mixed Harvest at Fall Clean up

In cleaning through all of my greenhouse starts I found more cabbage loopers decimating my dinosaur kale. I was able to salvage quite a few plants, but one plant was all but gone. They were also chomping on some cabbage starts in the greenhouse. So it goes…Regardless, I my vegetable beds are in pretty good shape for fall. I may need to tent them later, but today is fairly warm and sunny with rain showers on the way.

While cleaning out spent plants, I was able to harvest my one little pumpkin, several eggplant (the plants are still going!), some tomatoes, stumpy carrots and stressed, tiny cabbage and flying saucer squash from the bed now under renovation, and a few beans that went into the compost. The vegie beds are still producing with Bok Choi, chard, kale, lettuce, herbs all gearing up for the winter ahead.


  1. […] Contact | Garden Mentors Fava Bean Cover Crops in Seattle […]

  2. […] out to grab a few sprigs from the garden. Along the way I noticed destruction in my newly cleared, just-yesterday-fava-bean planted, needs-a-lota-love raised bed in front. Some critter has harvested many, if not all, of my fava […]

  3. Katy says:

    I have a cover crop of favas planted in one of my beds, in hopes of both fixing nitrogen and protecting the soil from the winter weather. But, the beans are about 2ft tall and starting to flower. I’d like to keep them in the bed all winter, but if I let them produce, will they still fix nitrogen? I’ve read that it’s important to turn them under before they produce beans – is that true?

    Thanks in advance!

  4. rhaglund says:

    We are having a strange autumn aren’t we? (Okay, I’m guessing you’re in Seattle). Here’s what I understand…if you let them flower and produce seed they should still fix nitrogen. I’ve pulled out green beans that are done for the season and they still have nitrogen fixing nodules on the roots. The reason you want to get them out before they go to seed is so you don’t end up with weedy seedy fava beans everywhere, or at least that’s what I understand.

    Now, if they flower and start trying to set seed now they may be more vulnerable to freezes when they come. But, do you have time to reseed right now? Its a tough call. I’ve put in cover crops late in the fall germination season and had luck. So, maybe soak a few of your remaining seeds overnight to soften them. And then plant another batch just in case this round doesn’t make it.

    So many plants think its spring with our warm fall weather right now!

  5. Katy says:

    I’m actually in the bay area, which is having crazy weather too. I’m not too concerned about the nuisance of the seeds spreading, these guys are pretty easy to control. Maybe I will try planting another set now, just in case. Another question – I bought these as a cover crop. Do you know if the cover crop cultivars are still tasty? It’d be great to be able to eat them.

  6. rhaglund says:

    Ah yes. I heard it was like 75 last weekend down there (Sunnyvale report).

    The favas I grow as a cover crop don’t produce tasty beans. I have tried them, but I wasn’t impressed.

    Given the weather you’re having, I’d definitely try another seeding. Just soak the seeds at least overnight to get them going a little faster.

  7. Maureen says:

    Where can I buy fava bean seeds in WA? Been looking but so far no luck finding any. Thanks.

  8. rhaglund says:

    Maureen, I’ve found them supplied at several retail nurseries around Seattle — Sky, Swanson’s and others. I believe many seed catalogers offer them as well. Good luck!

  9. Nitrogen fixation says:

    Nitrogen fixation by legumes are actually at the maximum when the plants flower. Legumes are protein(nitrogen) rich. That is why the rate of nitrogen fixation is the least when the plants are young and most when they enter into the reproductive phase. So legume cover crops will fix more nitrogen the longer they are allowed to grow in the garden or plant beds.

  10. anna says:

    nice article

  11. Judi says:

    Where can you buy fava beans in bulk in Seattle to use as a cover crop?
    Thank you!

  12. Judi,

    Unfortunately, it looks like Seattle Farm Co-op is on hiatus, otherwise, they could be a good resource for bulk farming supplies. Try calling farm suppliers in outlying areas. Too, many retail nurseries offer some bigger supply bags of fava (usually covercrop/not eating kinda) this time of year. Or, if you’re a non-profit, you could try calling some of the seed vendors themselves to see if they’ll offer you discounted rates (or even freebies) on older seed. (Fava is a big seed, which stores a lot of energy, so even older seed is likely to germinate just fine for several years past their “due date”.) Good luck!

  13. […] out to grab a few sprigs from the garden. Along the way I noticed destruction in my newly cleared, just-yesterday-fava-bean planted, needs-a-lota-love raised bed in front. Some critter has harvested many, if not all, of my fava […]

  14. […] as I was clearing out beds of summer vegies to make way for fall plantings, including nitrogen-fixing fava beans, I pulled out spent green bean plants. Green beans provide nitrogen fixation, doing the work in […]

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