The Pros and Cons of Cultivating Soil

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Tools for cultivating soil

In response to my recent post on Winter Mulches for Vegetable Gardens, reader Monica Reinagel suggested I follow up with more information on the pros and cons of cultivating vegetable garden soil. "A couple of times a year (spring and fall), I turn over my entire garden to a depth of about a spade and chop it up – to kill weeds (or turn under cover crops) and loosen up the soil. But I've read that it's best to do as little cultivating as possible so as not to disturb the top layer of soil. The turning and chopping takes a lot of effort. Should I stop?"

To answer this question, I looked into the effects of cultivation on soil nutrition, earthworms, beneficial fungi that live in the soil, and management of the soil's weed seed bank.

Shall we begin with some basic soil biology? The aeration caused by cultivation causes nitrogen to be released, especially in fertile, organically-enriched soil. This is fine when you're starting a new crop, but it makes less sense when winter is around the bend. For this reason, there are big differences between cultivating soil in spring, when planting gets under way, and digging about in the fall. In fact, nutrient losses from fall tillage and subsequent winter erosion make so little sense that Purdue University researchers have used the phrase "recreational tillage" for fall cultivation that makes soil look well groomed, but negatively affects its overall quality for growing plants.

In any season, earthworms can be the innocent casualties of unnecessary soil cultivation. Underground networks of earthworm burrows comprise a natural drainage system beneath many gardens, which is partially destroyed each time you cultivate. When the entire garden is dug and turned at once, earthworms may be forced to leave the garden in search of better habitat.

Broad fork
A broad fork is ideal for aerating the soil

Beneficial fungi that assist plant roots in taking up nutrients and water also are set back by soil cultivation, but they do not perish. But if you're going for truly superior vegetable garden soil, why interrupt the process? Austrian research indicates that building excellent organic soil with a full cadre of beneficial microorganisms can take as long as 15 years in a cold winter climate, so you don't want to cause unnecessary stops and starts by digging in when you could cover crop or mulch instead.

Gentle Soil Cultivation Guidelines

And so, in answer to Monica's excellent question, I propose the following guidelines for cultivating your vegetable garden soil:

  • Be as gentle as possible when cleaning up after spent crops, disturbing only the top few inches of soil. Save deep cultivation for when you are preparing soil for new plantings, and need to mix in compost and organic fertilizers.
  • Do use your spade to turn under cover crops, or to chop through the roots of spent plants to help them decompose faster. But when want to loosen and aerate your soil, a digging fork or a special tool called a broad fork (shown on the right) can do the job with minimal disturbance to the soil's secret world. A digging fork or broad fork is especially useful in spring and fall, when earthworms are most active. These are the worst times to use a rotary tiller.
  • Cultivate beds or rows individually, so that parts of your garden remain undisturbed. Earthworms, ground beetles, and many other beneficial life forms prefer stability to change.
  • Avoid cultivating in the fall if you can mulch instead. Pull out spent plants and compost them, and then scuff up the surface with a hoe to kill weeds. Mulch through winter, and save actual cultivation for spring.
  • Calendula weed seeds
    Calendula weed seeds - best not to turn the soil and dig these in!
  • Never cultivate when you know an abundance of weed seeds are present. Sweeping them up or sprouting them out makes more sense than mixing them in. Should an area of your garden receive a heavy rain of weed seeds, use the false seedbed technique to reduce the number of weed seeds present. This involves cultivating only the top inch of soil in spring, allowing the weed seeds to germinate, and then repeating the drill. The spot can then be planted with a fast-growing summer crop that quickly forms a dense, light-blocking canopy such as cucumbers or bush beans, and the rehabilitation is complete.

By Barbara Pleasant

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Comments

 
"Very useful indeed!! I'm very happy to watch the frost doing my work for me at this time of year! I've got some green manure in some beds, my Cavolo Nero is putting out secondary growth which we should eat between Xmas and spring. Still got some salads growing but I think that the forecast snow might put paid to that crop. The Chard probably needs to come out, although I have been advised that if left in the ground, I might get one more crop in spring before it bolts. Your opinion?"
Sue Lardner on Friday 26 November 2010
"I lay my compost in a two inch layer on the beds in autumn and let the worms do the rest and as you say it forms a weed mulch and does not chop up the worms and ruin their burrows, plus the big bonus it saves my back - perfect"
David fountain on Saturday 27 November 2010
" I'm somewhat new but well read.Still have a lot to learn.I'm using framed raised beds with a drip system.I tilled in with a mini tiller{ 6" } 2" of humus and then covered the beds with 4" of shredded up leaves. What do I do in spring?Till again,remove the leaves or what to do? What will the leaves and compost do to the ph?It's confusing with different opinions on the same subject. "
Tom on Saturday 27 November 2010
"Tom, because your soil is still in its early stages of organic improvement, it's hard to guess how much "digesting" it will do of leaves during the winter months. Wait and see, and don't worry so much right now. Your pH may be a bit wobbly for the next few seasons, but with enough good organic matter and lots of dynamic soil microorganisms, things will settle down and you will have a wonderful garden. I'd wait until the soil warms in spring to do any tilling, and then think about using a fork."
Barbara Pleasant on Saturday 27 November 2010
"I have two large older gardens, one 35'x75', one 17'x55' and one new 25'x40'. I am hard pressed to get enough compost to cover the entire gardens. My dad always tilled in the winter before a cold snap to kill the weeds and bermuda that always found their way into the rows. I didn't do any tilling this spring, having covered the gardens with about a foot of leaves in the fall, but planted each plant and seed with compost laid in the planting hole or down the row. We did not have a very good garden this last summer. I have decided to do it Daddies way and have started my cultivating today. I hate to chop up worms, but I missed my over abundance of veggies. I like to give them away. "
Joy on Saturday 27 November 2010
"Wot about cat poo? Is there a way to keep our feline friends at-bay?"
lucy on Thursday 27 January 2011
"Lucy, we have a whole article about how to keep cats off vegetable beds: http://www.growveg.com/growblogpost.aspx?id=165. Hope you find it useful."
Jeremy Dore on Thursday 27 January 2011
""Never cultivate when weed seeds are present" ??? I respectfully disagree. There is a difference between deep digging-in and cultivation. I definitely agree that deep digging-in should be done sparingly, and only seasonally to incorporate manures. However, unless you have loose sandy soil, and definitely if you have heavy clay soil, you should regularly cultivate 1-2 inches with a hand cultivator (it has that name for a reason) to loosen the top layer of soil; it will not harm the worms at all (it is the same tool I use when harvesting and feeding my worm composting beds) and will make a remarkable difference to your garden. It will 1)kill weeds and prohibit germination of new weeds, 2)get air to the roots of plants (by preventing a crust from forming), and 3)prevent excess evaporation of soil moisture; all by cultivating (loosening) 1-2 inches of the soil surface, which acts as a dust mulch preventing crusting and shading the lower soil, and by breaking the capillary action of the soil, which will prevent both evaporation and weed germination, and it is a mulch that is not in a state of decay, so it may be up against the plant stems without harm. Also, a dust mulch will encourage your plants to send their roots slightly deeper, making them more drought tolerant. PLEASE stop spreading cultivation misinformation. Deep digging-in should be done sparingly for all the reasons you have mentioned, but shallow hand cultivation is an invaluable weapon in the gardener's arsenal that should be explained to all and well utilized. The best way to help newbie gardeners is to adequately explain cultivation to them, not to scare them away by saying they will kill their worms and micro-organisms. Regular shallow hand cultivation will not cause harm. Excessive deep digging-in will cause harm, for all the reasons you have mentioned, but should more appropriately be called tilling, turning, or digging, not cultivation."
Sara (ForestGardenGirl) on Tuesday 8 February 2011
"Sara, thanks for your comment but I think you are meaning something different to Barbara when you refer to 'cultivating soil'. Many people use that to refer to deep digging whereas you are recommended the time-tested technique of just keeping the top layer of soil moving but never actually disturbing more than the top inch or two so that extra weed seeds are not brought to the surface. The same effect can be achieved by deep mulching rather than lots of hoeing, depending on the availability of good mulch."
Jeremy Dore on Tuesday 8 February 2011
"I appreciate your response, and I agree, we are talking about different things. However, if cultivating the top layer so time tested (and I must infer well known) why did I not hear about this shallow cultivating from any of my web or gardening book sources until 2 1/2 years after I began seriously gardening? What I am trying to say is, if you call digging-in cultivating, then how are you explaining this time tested shallow stirring of the top layer of the soil to newbies? I think the information is just not being shared (possibly because you think it is so rudimentary that everyone should know it, but I tell you, newbies NEED this information. Also, while everyone agrees good mulch is great, it harbors insects and rodents, and cannot be put directly up against any plant stems, whereas shallow cultivation does not have these draw-backs. Just my two cents- when I did discover this "time tested" method, it transformed my gardening practices and, if I may say so, I discovered this "time tested" method by reading a gardening book written over a hundred years ago -- and I am an avid reader, reading many dozens of well reviewed gardening books cover to cover, as well as many blogs. I highly doubt that I totally missed an entire section of each and every book and blog that I read. It is much more likely that it is so taken for granted by experienced gardeners, that they never think to tell newbies about it at all, and since there is this confusion about deep digging-in "cultivation" vs. shallow stirring of the top soil "cultivation", we can not discover our lack of knowledge except by accident (like I did). If gardening experts (like yourself) used a different word or phrase for digging-in and shallow cultivation, we might notice our lack of knowledge, and ask. Nevertheless, you use the term "cultivation" for both apparently, and we cannot know there is a double meaning for the term unless we are told. Just my opinion, but I think it is important enough to make a differentiation. But who knows -- maybe I am the only newbie in the world who has had this confusion; though I highly doubt this is the case."
Sara (ForestGardenGirl) on Thursday 10 February 2011
"I think you are specifically discussing the use of a "dust mulch," which works quite well during the growing season in areas with moderate rainfall and low winds. However, in very rainy and windy areas, or when used in the off season, it leaves soil open to erosion. I agree that this method should be in every gardener's toolbox, to be used when the situation calls for it."
Barbara Pleasant on Thursday 10 February 2011
"I have had raised beds for 20 years and these last two years have been a disaster especially with root crops I have three 5mtr x 1mtr beds and the two oldest are the worst I have not totaly turned the complete depth over aprox 500mm depth I believe I am under attack from root knot nemotodes and believe sterilisation or deep rotovation along with plenty farm manure would be the answer no mention in the article of bugs/diseases in raised beds ??"
Ian Geddes on Friday 19 August 2011
"Ian, rootknot nematodes make obvious nodules on roots, so be sure they are present before declaring war. Growing French marigolds en masse can starve them out, and solarization (must be done in summer) can set them back. Could it be something else? Two years ago I got mad at one of my beds and buried it in 4 inches of compost. It cured the problem. Still, a couple of my beds don't like root crops, go figure. I'm always happy when rotations bring them back to the most carrot-friendly spots. "
Barbara Pleasant on Friday 19 August 2011
"i have through years of gardening found it is best to just mulch with compost, and if the compost has been able to generate a high state of heat while composting this will kill most pathogens, my understanding is that soil is stratified in different layers each with different organisms and bacteria contributing to the whole, this also makes for less weeds, it takes a while for the baby growth to get started this way but once it does it is amazing."
dermot reilly on Monday 12 September 2011
"I usually till in the dead of winter, I believe the freeze at night will kill bores, and many other pest which hatch out and feast on the garden later. It seems to have worked really well for me. After winter, I may mow piles of dry leaves on the garden to add fiber to the soil, a little nitrogen fertilizer, soak it with a sprinkler, then cover the garden with heavy plastic. This forms a green house environment, raising the temperature in cold climate to 75 and upwards well over 100 F towards the spring. This will agressively promote growth of any seeds present including the unwanted weeds and grasses. The vegetation will sprout and die off because there is no sunshine. I leave this action going for 2 months or longer while my seedlings are beginning to sprout inside or in insulated makeshift greenhouses (small boxes or styrofoam boxes). The garden actually is cooking, spray with water occasionally to keep water available. Lifting the plastic once a month reveals tons of vegetation that grew and died off-amazing and mostly weeds. This warmth probably helps any earthworms to thrive, feed and regenerate becasue I have lots of them when I pull the tarp ready to plant after Easter with my ready sprouts. This method has cut back my weed and bug problems, allowing me a less maintenance demanding garden. "
Gario on Tuesday 7 February 2012
"As a veg gardener of 40 years I'm grateful for these W5 discussions: to cultivate or not to cultivate and how,why, when and where. Thank you. ps. it would be useful if contributors gave their geographic coordinates."
ingo ermanovics on Saturday 20 October 2012
"Great article and comments that have given me food for thought. Like Ingo, I've also been gardening for 40 years. I live in central Ontario Canada. For most of that time I have typically left the garden unworked in the fall and shovel dug for earlier plantings or tilled a little later as the soil became more workable. My Dad did the same for most of his life. This has worked well enough for us. You do have to add a good measure manure or compost because stirring the soil burns up nutrients. In the past few years I've begun experimenting with different methods. I've double dug to break up my hardpan clay, I've used green manure/cover crops and will try no til. I'm sure mulching is a useful practice however my chickens would rip the garden apart trying to get at the insects, beneficial and otherwise. Bottom line is... a good gardener is never to old or experienced to learn and trying new ways keeps us young and gardening exciting."
Bill on Tuesday 8 January 2013

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