Thursday, June 02, 2011

Perennial polyculture designs: five year review

This is part one of a three part series on perennial polycultures:

  1. Designs: a five year review
  2. Species profiles
  3. New designs


When we first moved to this site in 2006, I designed, on paper, elaborate perennial polycultures for tree understories. In each guild I included at least one plant to perform the main "food forest" functions: nitrogen fixation, nutrient accumulation (generally deep taprooted plants), beneficial insect feeding (plants in the carrot and sunflower families), aromatic pest confusing (onion family and mint family with their strong odors to throw off pests trying to find their preferred plant), spring ephemeral for early season nutrient cycling, ground cover, and foot tolerant path cover. I also wanted all the plants to have some direct human use, whether as food or medicine. And I tried to minimize inter-plant competition by matching vigorous runners with taller clumpers, plus designing for a combination of taprooted, fibrous, and flat rooted plants. I placed plants under each tree according to their sun requirements, designing for a fairly mature tree canopy casting significant shade (with some thought to the transition period of full sun in the early years.) And I matched guilds to tree root patterns, so that a taprooted tree would mostly have shallow rooted plants under it, and vice versa. Example polyculture design (1 MB PDF) I can't call these designs complete failures. The exercise of working them out helped me think through all the factors involved, and helped me learn the on-paper characteristics of many interesting perennial plants. I'm glad I did it. However, I never successfully implemented a single design, for several reasons.

Reasons for failure

Plant (Un)Availability

Our Process

To create my list of desired species, I diligently went through every entry in the species table at the end of Volume II of Edible Forest Gardens by Dave Jacke and Eric Toensmeier, plus all the species rated 4 or 5 in the Plants for a Future database. I added a few plants from books like Simon Hickmott's Growing Unusual Vegetables, local edible plant nursery catalogs, and odd mentions here and there. I came up with a great list of about 175 potential guild plants. I worked from the list to create my polycultures, then began tracking down the plants to implement the guilds. I hadn't anticipated the difficulty I would have locating the plants, even in the form of seeds which posed their own propagation learning curve. Over the last five years I've ordered hundreds of species of seeds from dozens of seed companies, spending hours researching and combing through plant catalogs. (My two most useful plant source search engines: Dave's Garden Plant Scout and UMN's Plant Information Online.) I managed to track down 90-95% of the species on my original list, though I kept adding more species of interest over the years, so that I still have dozens of species I would trial here if we were staying in this bioregion. Of the species I could find, only about 50% grew successfully. The rest never germinated, succumbed to slugs, got outcompeted by other plants, rotted from winter moisture, died with drought, or disappeared while we weren't watching. With the skills I've gained over the years in seed starting and with willingness to provide some extra babying to the most interesting species, I'd probably re-try another dozen or two of those failed species if we were staying here longer.


The long, drawn out process of tracking down seeds over several years, starting them up, waiting for them to get large enough to plant out, and having many of the attempts fail to produce a viable plant meant we never had all the planned species for a given polyculture at once. So my on-paper designs had to adjust to accomodate what I actually had available, with additions over the years as I successfully grew out new plants to incorporate. I still tried to make additions based on the original factors of guild function, top growth, and root patterns, but inevitably my incremental plantings lacked the full integration of my theoretical designs.

Inadequate Knowledge of Plants

I gathered as much information as I could on plant habits, culture requirements, and uses before designing my initial polycultures. But the books can only give so much detail on the intricacies of a living organism's life cycle, don't always accurately describe a plant's response to our particular climate and site, and certainly can't tell us whether we'll actually like eating the plant, or which part(s) we'll value the most, or what time of year we find the plant most useful.


Size, life cycle, & harvest methods: Skirret

The literature led me to believe that skirret (Sium sisarum) would grow to 3' tall by 1-2' wide. We've found that, on our site, that accurately describes a first year plant with its flowers, but older plants easily reach 5' tall and 3' wide. In mid-summer, after our typical weeks without rain, the first rainstorm or the first irrigation via our sprinkler weighs the foliage down so much that the whole plant flops right over. So my skirret placed carefully 1.5' from the edges of paths fell into them and created a maintenance problem. Other subtle details of skirret's life cycle and harvest methods affect how it integrates with other plants:
  • The roots radiate outwards in all directions from the central crown, necessitating a thorough excavation of the soil to find all the roots. So as opposed to something like garlic with a bulb easy to pull out without soil disturbance, skirret does not work well under trees and shrubs, nor next to perennial greens. Instead, it needs to integrate with other root crops or self seeding annuals.
  • The foliage dies down relatively early in the autumn, before the first frosts, allowing early harvest and potential cover crops or garlic plantings. Many of the roots we grow can't be harvested until November or later, so this timing makes a big difference in polycultures or time niche planning.
  • Skirret top stalks stay visible for several months into the winter, but by late winter or early spring they've rotted off, making it difficult to find the root locations. So it works best to have predictable locations for the skirret, or situations where it doesn't matter if some plants regrow in the spring where we missed harvesting.

Life cycle & harvest methods: Creeping bellflower

Creeping bellflower (Campanula rapunculoides) volunteered in our yard. I identified it, looked it up, discovered it's considered invasive in gardens as it runs rapidly but that the roots are edible, and devised a plan of allowing it to grow in place, with periodic harvesting of the roots from the edges to keep it in check.

Several times I dug up the edges to find the roots, but never found anything larger than spaghetti, tough and fibrous with nothing that seemed actually edible. I wondered whether this was a famine food, or if I had defective plants, or what. Finally I happened to dig into the center of my neighbor's patch of the plant, and discovered numerous sizable roots up to 3/4" diameter and 1' or longer! So apparently the plant only makes large roots over time, and my plan to harvest young roots from the edges won't work.

Parts used: Scorzonera & Dandelion

We originally planted scorzonera (Scorzonera hispanica) as a root crop. Soon thereafter, we learned that the leaves make an excellent lettuce substitute, so the plant became primarily a perennial green, with self-seeded plants as a bonus root crop. So rather than growing scorzonera in frequently disturbed soil in zone 2, we grow it in an undisturbed zone 1 bed. Conversely, we originally considered dandelion (Taraxacum officinale) just a leaf crop, best used during early spring then weeded out. Last year I discovered the roots make an excellent vegetable in their own right, providing a low maintenance root crop in the summer. So now we let the dandelions stay and harvest them from late spring til fall, when more desirable roots become available.

Inappropriate zone placement

I missed a very basic permaculture principle with many of my original polyculture designs. I didn't pay attention to what sort of yields went under which trees in the yard, and their accessibility from our front door. So I had leaf crops designed under trees in the far corner of the yard, which in practice I would almost never get around to harvesting.

Crop balance

When I first designed our guilds, I had no concept of how many leaf crops we would need vs roots, shoots, berries, seeds, etc. Since the perennial plant world offers many greens but relatively few foods from the other categories, I overdesigned leaf crops by default.

Difficulty implementing self seeding annuals

I sometimes consider myself a terrible gardener, such as when I have to admit that I failed--several years in a row--to grow pigweed (Amaranthus sp) and lambs quarters (Chenopodium album). You know, those weeds that gardeners everywhere else persistently pull out of their beds year after year. I tried several different species of amaranth, and at least two of Chenopodium, and I don't think I ever got any to grow the first year, let alone persist as an annoying weed. My original designs incorporated several other self seeding annuals: breadseed poppy (Papaver somniferum), miner's lettuce (Montia sp), land cress (Barbarea verna), corn salad (Valerianella locusta), and some biennials like evening primrose (Oenothera biennis). Only the evening primrose has really succeeded here; the rest never got started or have failed to robustly self seed. I attribute the failures to our heavily mulched, rarely dug soils. The first two years (especially the first), everything had a thick layer of wood chips. I tried spreading a thin 1" layer of soil in some places to seed plants like the amaranth & chenopodiums, but those tend to germinate in late spring or early summer with more heat, which coincides with the end of our rains and thus drying out of those 1" layers of soil. In subsequent years, we had heavy slug pressure, and rarely had bare patches of soil with full sun to support such pioneering annuals, especially late in the season. I did include root crops amongst those self-seeding annuals in my original design, to facilitate creation of bare soil, but with the exception of evening primrose (whose root I dig over the winter), those combinations of digging & self-seeding never really came together.

Spring Ephemerals Not So Useful

I made a small design mistake by including, in each guild, a spring ephemeral as suggested in Edible Forest Gardens. These ephemerals begin growing in late winter or early spring, taking advantage of full sun conditions before shrubs and trees above them leaf out. They flower early in the season, then die back to the ground as shade increases. On the east coast, with its harsher winters and frequent late winter snowpacks, these ephemerals play a crucial role in "catching" nutrients early, preventing snow melt or rains from leaching them out before the woody plants come into growth. In the pacific northwest, we have mild winters with many warm spells throughout the winter allowing some plant growth. In Portland we never get a real snow pack. Here it makes more sense to incorporate evergreens or fall planted crops such as garlic and fava beans. The ephemerals I've tried have competed poorly with other perennials and the late winter/early spring annual weeds.

If I Knew Then What I Know Now...

If I had the opportunity to do this all again, I would:
  • Design with the plants available to me, so I could plant them all out at once. (I would reserve some areas as nursery & trial beds for new experiments.)
  • Plant out low growing or easily removable ground covers everywhere I'm not yet ready to implement permanent designs. Selection criteria:
    • Evergreens preferred
    • Winter leaf crops
    • Berries
    • Duck forage
    I haven't put much thought into this, but some ideas on species:
    • Evergreen violets such as Viola odorata (edible leaves & flowers)
    • Evergreen bellflowers such as Campanula poscharskyana and C. portenschlagiana (edible leaves & flowers)
    • Bunchberry (Cornus canadensis) as a native berry crop. This did poorly in early years, but might succeed now with more shade from maturing trees.
    • Various low growing Rubus species, such as R. nepalensis, R. tricolor, R. x stellarcticus, R. arcticus, R. pentalobus.
    • Strawberries, both garden variety and species (Fragaria sp.)
    • Perennial ground cherries (Physalis sp.)
  • Plant fewer greens, and concentrate them closer to the house since I pick them once or twice a day.
  • Plant more perennial seed crops.
  • Try to design a soil disturbance regime to suit self seeding annual seeds from Amaranthus sp. and Chenopodium sp.
  • Incorporate ducks to reduce slug pressure on leguminous seed crops of favas, peas, and runner beans.
  • Include more evergreens in general rather than spring ephemerals
  • Group root crops together for complementary soil disturbance. I'll post soon with several root polyculture ideas I'm trialing this year.
  • Skip the nitrogen-fixing function from my list of guild requirements. One person can fertilize 4000-5000 square feet of forest garden with urine.


Mr. H. said...

I enjoyed hearing your thoughts on edible perennials, especially skirret...a plant we hope to include in next seasons garden. Glad to see that we are not the only ones that include nutritious dandelions on the perennial plant list.:)

Rhizowen said...

This is an excellent (and searingly honest) analysis of your polyculture project. For me it shows just how site specific each system will be. The only way to acquire that knowledge is through careful observation and protracted experimentation. Great stuff.

Norris said...

I just added a section above on creeping bellflower, under "Inadequate knowledge of plants." I often relate this example to folks on tours, to show the pioneering nature of trying out unusual perennials, as the literature often lacks crucial details.

Anonymous said...

just found your page- thanks for putting so much thought and effort into sharing your experiences with the internetting public. i'm looking forward to reading more and will be happy to share resources on those hard-to-find plant/seed sources should i come across them!

Lincoln Smith said...

Wow, this is perhaps the most useful analysis and trial report of polyculture design I've ever read. Thanks!

Ottawa Gardener said...

As for creeping bellflower. I used to dig up the whole patch. It always grew back... Yes,I find that some soil disturbance is necessary to rejuvenate annuals. Depending on the annual, not much is needed.

SarahLinsey said...

Thanks so much for this! I'm going to suggest that we integrate some kind of a project evaluation exercise as a workshop for our Ottawa Permaculture Convergence this spring...learning from our own (and each others') mistakes and successes is really helpful.

Anonymous said...

Skip the nitrogen-fixing function from my list of guild requirements. One person can fertilize 4000-5000 square feet of forest garden with urine.
Considering this, and your proposal makes sense from a nitrogen-perspective, NFT's often grow fast, can open up tough soil with their roots and return mined minerals to their leaves and tissue. After cutting them and leaving them on the soil, you and encouraging fungal growth which benefits the soil and plants. Urine won't encourage fungus like lignin will. If not using nitrogen-fixing, at least add fast-growing small wood shrubs that maybe have other crops as well as their timber for fungal purposes.

Great post by the way.

Norris said...

Thanks for your comment, anonymous! That's a great point that the soil-prep nature of NFTs is a worthy benefit in and of itself. Though in Portland we had easy acceess to all the woody fungal-feeding material we wanted via free loads of wood chips, that won't scale up to every yard, so even households importing food and peeing out their nitrogen will benefit from fast-growing woody material.

I've also posted some other reasons why we still love the N-fixers.

Vibrations said...

Very very informative! I want to make a polyculture with amaranth and chenopod too. Did you finally came up with a functionning polyculture system ? Thanks!

Norris said...

Hi Vibrations,

We had success with the amaranth & chenopods in the first year, but we didn't wind up with any reliable self-seeding polycultures with them. That wasn't as much a priority as the perennial polycultures, so I'd bet there's a way to make them work with more experimentation.

Good luck, and please post back here with your own results!