Food for Thought


The San Francisco Chronicle’s garden advice columnist Pam Pierce wades into the murky debate over mulching, double-digging, and amending the soil.  It’s a tricky business, but she sums it up neatly.  Read the whole thing here.  This, I think, is the most compelling argument against this particular practice:

A second reason is the
bathtub effect. This refers to what often happened in the past, when
gardeners followed advice to excavate a hole at least 2 feet deep, then
heavily amend the soil they put back in, under and around the
transplant’s root-ball. Often the planting hole, because it was filled
with soil so different from that surrounding it, did not drain well. It
filled up like a bathtub with a clogged drain and the plant’s roots,
lacking air, drowned.

And so, once again, we are left to sift through this hodgepodge of ideas about dirt. (I’m not calling Pam’s column a hodgepodge; she does a great job of making sense of the larger confusion about this issue.) When we decide to double dig or not to double dig, are we following expert advice? Or proven techniques backed by research?  Or feel-good tips based mostly in instinct?  How do we know the difference?  Does it matter?

Here’s what I wonder: how is gardening advice different from cooking advice?  If you’re trying to make dinner, you have a wide variety of recipes you could follow, and perhaps a few hard-and-fast rules, mostly having to do with food safety and basic chemistry, but is the overall approach less dogmatic?  Geared more toward suggestions, inspiration, taste, and what ingredients are available?

Or is it the opposite?  Are food people even more dogmatic and rule-driven? Are they for ever discarding the conventional wisdom about, say, the proper technique for boiling an egg or making the perfect tomato sauce, and replacing it with the latest and greatest advice?

Does anyone know anything?  Just wondering.



  1. I think it’s important to be clear, here.

    There’s hard, reproducible scientific evidence for not amending planting soils, but rather fitting the plant to the site, not the site to the plant.

    This is just the same as the science behind why various ingredients are added to recipes when baking cakes, etc.

    As long as the science behind the landscape design or recipe is followed, than success with the creative part of the process is more likely.

    One more thing, I find the comment from a garden writer, “One reason not to amend landscape trees and shrubs is that they grow faster in amended soil, and this may not be what you want. A landscape plant that grows faster will often need more pruning and may outgrow its space faster,” to be utterly perplexing!

    If one puts the right plant in the right place, it should never be necessary to prune it – then set the “debris” at the curb to be hauled away!

    As environmentally sensitive/sustainable types, shouldn’t we be focusing on using fewer inputs – not encouraging the status quo?

  2. While pairing a plant’s needs with soil type is important, some soils need help before much of anything will grow. In particular are those that are compacted or have had the topsoil scraped off for construction & then had a dusting of topsoil sprinkled on top when construction finished. These soils need help before even weeds can thrive. However, the efficacy of double digging has been called into question. The thing that seems to work best is dumping copious amounts of compost on top of the soil & letting nature take its course. In a wood, the fallen leaves become the soil, in the meadow or prairie, the grasses & dead plants fall to the ground to be incorporated. Gardeners must mimic these processes for soil & plants to thrive.

  3. When I started my prairie vegetable garden, I double dug it and put a layer of leaves and then compost in the bottom of the trench. The soil was extremely light, almost literally dust which blew away if we had a strong wind. Below was sand. There was not an earthworm to be seen.
    From then on compost and manure was just dug into the top layer in Fall when the growing season was over. Worms, veggies and flowers thrived.
    It seems to me that the efficacy of double digging and amending the soil around newly planted shrubs etc depends on the soil. My assumption about amending soil for newly planted shrubs is that it gives them a good start. Once established they have a better chance of surviving in whatever the garden soil offers.
    In the end it comes down to observing your soil and working out what it needs to be productive and whether it needs anything. In my mountain garden I have plants growing in a path built of grit, small stones and pebbles!

  4. Good grief. If I didn’t amend my clay-and-rock ‘soil’ to improve drainage and actually MAKE some soil, about the only things that would grow here would be cattails, moss, weeds that like compacted wet heavy soil, and grass; all of which are fine enough in some circumstances but a little dull for a garden.

    While the column and this blog posting provide excellent food for thought, I hope no one, especially newbie gardeners, gets discouraged. After all gardens are as individual as the gardeners creating and tending them, just as there are seventeen dozen or so ‘excellent’ recipes for brownies or chicken cachiatore.(sp?) There will always be arguments about whether to add compost or to double dig, what to use as a mulch, whether to use chemical warfare or not, whether you’re only a good gardener if you use native plants (native to where? How long ago constitutes ‘native?)…we humans aren’t happy unless we’re arguing about something, even in gardening.

    To which I say bloom where you’re planted, plant what gives you joy, (embrace your earthworms even though they’re ‘invaders’) and do try to be as organic as possible–without becoming militant about it.

  5. “One more thing, I find the comment from a garden writer, “One reason not to amend landscape trees and shrubs is that they grow faster in amended soil, and this may not be what you want. A landscape plant that grows faster will often need more pruning and may outgrow its space faster,” to be utterly perplexing!

    If one puts the right plant in the right place, it should never be necessary to prune it – then set the “debris” at the curb to be hauled away!”

    I agree regarding the never outgrowing its space if its the right ultimate size plant side of this argument but there can be instances (and I’ve seen this with my own plants) where certain high growth woody plants grow up top faster than their rootball catches up as a result of overfertilizing/amending the soil – end result either the whole plant gets torn up by wind or all that new shiny growth gets snapped off by the wind. Either way I don’t amend my planting soil for anything woody reaching higher than about 4 feet.

  6. thank you! this is something i wonder about as a novice gardener. i find a wealth of advice on the internet, but have a hard time with my meager experience sifting through it.

    and i think you’re right to compare it to cooking. it has more to do with the philosophy of why someone gardens. i can imagine that i choose to fit plants to sites rather than sites to plants for scientific reasons; but i’d be lying if i didn’t also mention how much it pleases me to feel like i’ve read the earth correctly. there’s a harmony i seek in parallel to success.

    just last week i think i told someone i thought it would be “cheating” to add worms to my compost heap. not that i think anyone who does is cheating, but if i added them myself, i wouldn’t get to know when the neighborhood worms found it. we can acknowledge our preferences without letting them get in the way of sharing information. similarly, i try to hold my philosophies aside when i’m learning, to keep them from applying value judgments to what might be great advice. it’s not impossible for bill o’reilly to tell me the truth. just extremely unlikely.

  7. Gardeners as a lot are not going to be satisfied with only fitting the plant to the site due to the existing soil conditions. Yardeners may well go for that, hell yardeners do that and end up with lots of sad pathetic never needing to be trimmed bug encrusted attempts at full planthood.

    Gardeners want healthy, happy, robust and productive plants and they are going to give them the soil they most prefer whether it pre-exists or they have to create it themselves or by bringing in good soil.

    My totally lazy non-toxic approach is just constant addition of organic material on top as a mulch that I leave for the soil biota to till and digest and make available to the plants just like they do in natural ecosystems.

    I’m a gardener. I want to assist my plants to a better soil so they are not constantly looking around for a better soil to move to.

  8. I just ignore whatever advice is given under the rubric of horticultural science and do as little as possible to make my conditions similar to the plant’s native environment.

  9. There are rules in cooking, but not nearly so many variables. You don’t need to worry whether your cookpot has adequate clay, silt loam, minerals or heavy metals. (The cookpot probably has plenty of heavy metals). You don’t have to send your cookware out for analysis. Nor do you need to worry about the microbe factor in your cake mix.

    In fact, I would say there is more unknown about how plants and soils work together than there is known. That may be why people are so apt to follow what works, rather than what someone says is supposed to work or won’t work.

  10. Ijust throw some compost in the hole. Maybe that’s why I’ve never been able to successfully boil an egg. I need to get more scientific about my cooking and my gardening.

  11. Faneuil Hall – Quincy Market Place in Boston is another wonderful historical market place .
    It was built in the late 1820’s to service the local farmers market and tradesmen and is still going strong.
    If you are in the area check out the great old black and white photographs that hang in the hall.

  12. I ADORE Faneuil Hall – always head there when in Boston with at least $50. to blow on fun stuff…and that fab seafood restaurant famous for its clam chowder & oysters – Durgin Park??? Even Adams and Jefferson enjoyed it! YUM!

    The great photo above shows the market that was filled with pushcarts selling all sorts of wares – pots, pans, dishes, etc…not so much food…as did “Paddy’s Market” that stretched along 9th Avenue from present-day Chelsea, through Hell’s Kitchen to around 41st St.

  13. fantastic photo…add a little colour, reduce the size (of the market) and introduce a bit of corrugated iron into that facade and you’d have the Barossa Farmer’s market, South Australia. a place to spend blissful Saturday mornings deciding whether to buy a piece of Berkshire pig or a free-range Australorp for Sunday lunch…

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