Tag: soil

Podcast #8 – Water Works

We’ve finally gotten our summer here in the Pacific NW and it’s been pretty hot for a few weeks. The plants weren’t really prepared for this, so we’ve had to irrigate quite a bit to keep all that lush foliage happy. So the topic of this podcast is Water Works – focusing on how water moves in the soil and through plants.

One of the more interesting tidbits I found this week is a recent USDA study on growing more potatoes with less water. Sound impossible? Listen to find out the one single, simple thing that increased water use efficiency by 12% and reduced fertilizer runoff as well.

I also debunk the common myth about using drainage material in container plants. Research from 100 years ago demonstrated that water won’t cross textural barriers – so putting gravel in the bottom of the pot will actually create a bathtub effect rather than helping drainage.

The interview this week is with my garden – primarily the sunny south-facing side. I thought I’d take you on a tour to see what’s happened in the last 11 years. The photos below will help you visualize the interview.


The front yard in 2003. We’ve started taking out the turf and moving around trees and shrubs.

The front yard in 2003 from another angle. We’ve removed the second driveway and covered the area in wood chips. By the garage you can see two of the roses I dug up from the shady back yard and moved to the sunny front.

The new front yard, with fencing, more plants, a pond, and no turf.

The rhody-hydrangea corner in front of the arbor vitae hedge

The new street garden, with a new retaining wall to hold back the soil that used to wash into the street.  Everything not covered in plants is covered with wood chips.

This is the last podcast of the first “season” of The Informed Gardener. We’re going to take off for about a month before starting the next series. If you’ve got ideas about future topics, you can email me or post a comment here. In the meantime, you can listen to archived podcasts found on this blog; just click on “podcasts” on the right-hand menu.

Our visiting GP takes on fertilizers

Like many readers of this blog, I’m like a kid in a candy store where plants are sold.  I try to justify the extra cost of a large annual pot instead of a scrawny 4-pack, or I imagine I’ll find room for that lime green Heuchera and my wife will learn to love it.  But unless I keep my blinders on and stick to the shopping list, I’ll probably leave with a fertilizer.  This year, I’ve purchased 12-0-0, 5-6-6, sulfur, and some 5-1-1 liquid.  Those go with my 6-9-0, 11-2-2, 9-0-5, 2-3-1, and 4-6-4.  I can explain why I ‘need’ each one.  I have a decent idea what my soil is like because I’ve had it tested (though I’m due for another test). But I’ve always questioned how those bags of fertilizer can know exactly what my garden needs.  The rates listed on the bag imply they’re universal under all circumstances and will give great results if the directions are followed.   Is that true?   And at what cost?

For example, 2 of the bags are listed as ‘lawn’ fertilizers (the veggie garden doesn’t care about that though).  But if I apply these to my lawn at the rate listed and 4 times per year, I’m adding 3-4 pounds of nitrogen per 1000 ft2.  That’s a reasonable rate if I irrigate and bag my clippings, but I don’t do either.  Therefore, I only need ~1 pound of nitrogen, not 3 or 4 (see this publication for more info). I just saved myself some money by disobeying the bag. That extra nitrogen isn’t useful for making MY lawn healthy.

One of my fertilizers is labeled ‘tomato’.  If I do exactly as the bag tells me for tomatoes, I would be applying the equivalent of 400 pounds of nitrogen and almost 500 pounds of phosphate per acre.  So what?  Well if I look at a guide for how to grow tomatoes commercially, I’d notice that the recommended nitrogen rate is 100 to 120 pounds per acre, and phosphate is 0 to 240 pounds per acre.  Yes, those are commercial guidelines, but they shouldn’t be too far off from garden recommendations. And of course, recommendations should always be based on soil tests.  But 4 times the N and 2 to infinitely more times the amount of phosphate than is required? That’s likely a waste of money at least. And yes, those recommended guidelines are real: you CAN grow food without adding phosphate or potassium-containing fertilizers.  If the plants you’re growing don’t need much and your soil has plenty, you don’t need to add any.

Say I’ve got an acre of onions (Fig. 1; not quite an acre). One of the bags of fertilizers, were I to follow its instructions for fertilizing ‘vegetables’, tells me that I should add 100 pounds of nitrogen and 120 pounds of phosphate and potash at planting (per acre), followed by half that partway through the season (next to the row). The commercial production guidelines tell me that the nitrogen rate is similar to what the bag of ‘vegetable’ fertilizer says, but I actually need about 7 times less phosphate and potash (based on my soil test results; I have quite a bit of P and K already in my clay-loam soil). I don’t want to add stuff my soil doesn’t need, so I use my shelf full of bags, a scale for weighing pounds of fertilizer per cup, and some math to come up with a custom fertilizer regime that suits my soil and the onion’s needs (see Table 1, and remember that the numbers are for MY soil, not necessarily yours).

One problem with using extra fertilizer may be in the extra cost (wasting nutrient the plant won’t use), but that depends on what fertilizer it is and how much it costs. Another problem may not be immediately apparent, and that is nutrient deficiencies. Too much phosphorus can cause zinc deficiencies, for example. Excesses of some nutrients can create greater chances for pest and disease problems. One big problem with using too much is the potential for these extra nutrients to go where they shouldn’t be, like in groundwater, rivers, lakes, and streams. And as Jeff has mentioned, phosphorus fertilizers won’t be around (cheaply) forever.

Do the work of figuring out what kind of soil you have and what’s in it, what your fruits and veggies need, and what kinds of fertilizers can do the job for you.  Heck, you can even organize your fertilizers based on “cost per pound of nitrogen” to see where the best bang for your nitrogen buck will be.  But none of us are THAT obsessed about our fertilizers, right?…. [$ per bag / (pounds per bag * (% nitrogen/100))].

As a reminder, the numbers on your fertilizers are percent nitrogen, phosphorous (as ‘phosphate’, P2O5), and potassium (as ‘potash’, K2O).  One cup is 16 tablespoons, and an acre is has length of one furlong (660 feet) and width of one chain (66 feet), or 43,560 square feet.  Side rant: metric rocks.

A rant about urban farming

(I know this one will get me into trouble…but hey, if I don’t tick someone off I’m not doing my job.)

I have mixed feelings about the increased popularity of urban farming. On one hand, I love the idea that people are becoming more involved in producing their own food. But on the other hand, the naivety of many urban farmers is scary – because they assume that home-grown food is safer and/or healthier than what they can buy at the market.

I give a lot of seminars every year, on a lot of different topics. At the end I usually have a room full of happy people, asking lots of questions and eager to go apply the new knowledge that they’ve gained. But one talk I’ve done has exactly the opposite effect. It’s the seminar I give on vegetable gardens and heavy metal contamination of urban soils. The audiences are subdued and worried. It doesn’t make me feel very good, but on the other hand I know I’ve got people thinking.

Heavy metal contamination of soils is insidious.  Like the iocane powder in The Princess Bride, these compounds can be odorless and tasteless…and deadly. Lead, arsenic, cadmium, and a handful of other heavy metals are the legacy of centuries of “civilized” living. Mining, smelting, manufacturing, and driving all contribute to localized toxic hot spots. Unlike organic contaminants, heavy metals are elemental. They don’t break down and go away. The lead from gasoline fumes of the past is still found along roadsides; the arsenic from early pesticides still lingers in soil used for field and orchard crops. Many plants not only take up heavy metals, but accumulate them in their tissues.

It’s easy to avoid heavy metal problems: soil tests are the logical first step. If soils are contaminated, you can build raised beds or use containers with clean, imported topsoil or other growing media for vegetable gardens. Likewise, you might want to take care in buying produce from farmer’s markets – ask questions about possible soil contamination.

So by all means, grow your own vegetables – save money and take satisfaction in producing your own food. But be careful out there.

Mortal Kombat – garden version

Soil solarization is regarded as an environmentally friendly alternative to pesticides for controlling nematodes, weeds and disease.  Sheets of plastic (generally clear) are spread over the ground and solar energy heats the soil underneath to temperatures as high as 55C (or 131F).  Since the soil environment is usually insulated from temperature extremes, the organisms that live there are unlikely to be resistant to heat stress.

This is a practice best suited to agricultural production, where monocultures of plants have attracted their specific diseases and pests.  Decades of research have shown success in controlling pests in greenhouses, nurseries, and fields.  But there’s a down side to this chemical-free means of pest control.

It shouldn’t be surprising that beneficial soil organisms, in addition to pests and pathogens, are killed by solarization.  Studies have found that soil solarization wipes out native mycorrhizal fungi and nitrogen-fixing bacteria.  One expects that other beneficial microbes, predacious insects, and parasitoids living in the soil (but so far unstudied) would be eliminated as well.

This may be an acceptable loss to those who are producing crops; soil can be reinoculated with mycorrhizal fungi, for example.  But for those of us caring for our own gardens and landscapes, this is literally overkill.  (And consider that most of us probably have trees and shrubs whose fine roots extend over our entire property.)

So this spring, instead of solarizing your soil, consider some less drastic measures of pest and disease control. Minimize soil disruption to preserve populations of desirable microbes. Plant polycultures (more than one species) in your vegetable garden, or at least practice crop rotation.  Protect and nourish vegetable gardens with compost.  Use coarse organic mulches, which provide habitat for beneficial insects and spiders, in landscaped areas.  Above all, try to treat your soil as the living ecosystem it is, rather than a war zone.

Is “lasagna gardening” really worth the effort?

This week I got a complimentary copy of Urban Farm, dedicated to “sustainable city living.”  The cover story is Lasagna Giardino – follow this recipe for a lasagna garden that grows perfect plants – Italian or not.

This is not a new idea, but was popularized several years ago as a way of preparing soil for planting.  The article relates the steps:

1)  Prepare the ground by mowing the lawn
2)  Dig up the first 12″ of soil (double digging)
3)  Place a layer of “noodles” (paper and cardboard are popular) – the low nutrient material
4)  Place a layer of “sauce” (the green material)
5)  Repeat as often as you like and “let it cook”

I like the first step of this.  But my second step would be:
2)  Add a thick layer (12″) of arborist wood chips and “let it cook.”

Double digging the soil 12″ isn’t necessary: we do it because it’s hard work, and we think we need to put elbow grease into the project.  Making layers of noodles and sauce isn’t necessary: we do it because appeals to us -lasagna is a tasty comfort food.

There’s a lot of damage that this “recipe” can cause.  Double digging the soil 12″ destroys soils structure. Don’t do it. The layers of noodles and sauce (especially the sauce) can create an overload of plant nutrients. Furthermore, the “noodle” layers – the sheet mulches – impede water and air movement.  They’re not needed to keep the grass from growing through. Wood chips do this just fine on their own.  And don’t worry about that initial 12″ of chips.  Within a few weeks it will settle to about 8″.  Let it sit for several weeks.  Then pull aside some of the chips and take a look.  If the process is done, the grass and/or weeds will be dead and decomposing – a natural compost layer.  You can then plant whatever you like.  Reuse the chips somewhere else in your garden.

It doesn’t look like lasagna, but it’s a heck of a lot easier and more closely mimics a natural mulch layer than lasagna does.

Should we use biochars in our gardens?

In the last few years, I’ve had a number of people ask me about biochar:  what  is it and what does it do?  Should they add it to their garden?  Should they make their own biochar?  So while the subject deserves a longer review, I thought it would be useful to discuss it briefly on the blog.

In the strictest sense, “biochar” refers to charcoal that’s made as a byproduct of biofuel production.  Various crop residues, livestock manures, and just about any other organic material you can imagine has been studied for this purpose.  Biofuel production not only helps diversify our energy resources, but the biochar itself also boasts several benefits, not the least of which is that it serves as a long-term, stable repository of carbon.  Since the carbon in biochar decomposes so much slower than the parent organic material, it is often considered to be a “carbon negative” material.

Even more exciting is that biochar offers some distinct, tested benefits to agriculture.  It is a porous, charged material that has been used to remediate soils by binding contaminants such as pesticides and heavy metals.  It offers a physical environment to mycorrhizae, which often benefit from biochar amendment.  It binds nutrients such as nitrogen, preventing runoff or leaching, and releases these nutrients to crops, most of which are shown to benefit from biochar additions.  The scientific literature is robust in examples, worldwide, of how various biochars benefit agricultural soils and crops.

But before you rush away to buy (or make) your own biochar, there are some significant caveats.  First, there is a sophisticated process used to make biochars, whose characteristics will vary tremendously depending on how they are produced.  Differences in temperature, for instance, will produce very different biochars from the same parent material.  (And you would be hard pressed to do this at home:  temperatures can range from 100-700C.)

Second, there is little, if any, research on the use of biochars in nonagricultural situations other than soil remediation.  This means no information on how it affects trees, shrubs, home gardens and landscapes, and other urban greenspaces.  As readers of this blog should know by now, there are many agricultural production practices that do not translate well to the home garden or landscape.

Third, biochars are generally very alkaline, often with a pH close to that of lime.  While this might be fine for some soils and plants, naturally acidic soils and their respective acid-loving plants are not going to react kindly to a more alkaline soil environment.

Finally, I hate to see people (and they are out there) who are now taking their pruning debris, arborist wood chips, and other organic material, burning it, and burying it.  Ideally, both bio-oils and biochar are made from excess crop residues and other debris generated in agriculture.  Arborist wood chips and other plant debris generated in a home landscape need to go right back onto the soil as part of a compost/mulch layer.  To burn this valuable resource strikes me as the classic “penny wise, pound foolish” mentality.

Of Worms and Fertilizers

Today I’m going to write about fertilizers and worms.  The purpose of this post is not to encourage you to use fertilizers.  I agree wholeheartedly with Linda’s post – we don’t need many of the fertilizers which we’re using.  Still, it’s important to know the facts about anything that you’re doing (or not doing) to and for your garden, and to do them (or not do them) for the right reasons.  With that in mind, I’ve been reading about worms and fertilizers for the last few days and wanted to let all of you know the basics of what I’ve been reading, because it is somewhat contrary to what many gardeners believe.

Before we begin let’s get one thing straight — worms are basically good for your garden and your plants in general.  We like them!

Over the years I’ve heard all kinds of comments about how inorganic fertilizer is bad because it kills worms or drives them away.  For the most part I’ve just accepted these claims as generally true because it seemed to make sense and I didn’t have a reason to study it further (I don’t write about worms much, and I’ve never spent any time doing research on them – still, I have to admit that this is no excuse for ignorance).  The only contrary words I’d ever heard spoken about the reality of what fertilizers do to worm populations had come from a soil scientist friend of mine who told me, in casual conversation, that he didn’t believe that fertilizers were bad for worms at all, except, perhaps in the very short term if they got some fertilizer directly on them.  Rather, he believed that, because fertilizers encouraged the growth of plants, fertilizer use would actually increase worm populations because it would increase their food supply.

After reading through a few papers it looks like my soil scientist friend was right.  Here I’m going to summarize my general impressions about these papers into a few sentences – not exactly fair because the relationship between worms and fertilizers isn’t completely straightforward – but hey, this is a blog!  Basically, if you add fertilizer of any sort to your soil you will ultimately increase worm populations because you will encourage the growth of more plant material.  More plant material, over the course of time, means more organic matter for worms to eat.  Generally organic fertilizers seemed to be preferred by worms (probably because they include lots of organic material along with the nutrients which they offer), but overapplication of fertilizer (organic or inorganic) could be bad for worm populations, at least in the short term.

So, in a nutshell, judicious fertilizer use shouldn’t affect worm populations negatively.  Still, why add fertilizer at all if you can avoid it?  Mulch and compost – worms will definitely enjoy that!

Fertilizers, crops and landscapes

Last week Jeff wrote about the dangers of using “balanced” fertilizers, especially in reference to phosphorus content.  Comments quickly followed about using fertilizers in many situations – on farms, in container plants, on trees – and so on.  One of the latest comments came from Nick and began “I don’t usually recommend fertilizer for perennials or woody plants to consumers. In most cases they aren’t needed.”  And this leads into today’s topic.

Many of the horticultural practices we use in our gardens and landscapes have, unfortunately, been derived from agricultural crop production.  Whether you’re growing a field of wheat, garden tomatoes, or containerized shrubs your goal is maximizing crop production.  By its nature, this is an unsustainable practice because it requires continual inputs of water and nutrients at higher levels than would naturally occur.

But this is not how you should care for landscape trees and shrubs, and why Nick’s comment was a good one.  You don’t need to routinely add fertilizer to these plants; they don’t need it to grow normally.  What we should be doing in landscapes is preventing nutrient deficiencies.  Once you have a soil test in hand, you’ll know what nutrients may be too low (or too high) and how soil pH will affect that.  For most of us, this may involve occasionally adding one of a few nutrients (most commonly nitrogen), or perhaps acidifying the soil to improve nutrient availability.

 How do you know when to add nitrogen to established landscape plants?  Let your foliage do the talking. If leaves are uniformly yellow, small and sparse, you might have a nitrogen deficiency.  This will be most common in the mid to late summer, when plants are growing most rapidly and competing with one another for resources.  Be sure this symptom is wide-spread, however.  If it’s just one plant showing deficiency symptoms, it’s probably not a landscape issue.

 

Building healthy soils?

I love living in Seattle…but I’m getting increasingly impatient with the City’s “Building Healthy Soils” propaganda.  For years I’ve questioned their recommendation to perpetually amend landscape soil with organic material to no avail.  Let’s see what you all think of their “fact sheet” (which you can read here in its entirety).

“The best way to improve the soil is to add plenty of compost or other organic matter throughout the entire planting area before planting. Thoroughly mixing these materials deep into the soil helps provide water, air and nutrients to plant roots.”

Hmm.  No mention of how to determine IF your soil needs improving; without a soil test, you have no idea what your baseline organic matter level is.

But perhaps this recommendation is only for vegetable gardens and annual beds?  Nope.  In the next paragraph, we’re told to “Mix in organic material before planting lawns, perennials, trees and shrubs.”  We’re given helpful how-to instructions:  “Use a shovel or digging fork to mix amendments into the top 6 to 12 inches of soil. It is important to amend the entire planting bed — not just small holes for each plant. When planting individual trees and shrubs in lawns or existing beds, amend an area at least 3 feet wide, or 3 to 5 times as wide as root balls over 12 inches in diameter. Rototill large areas where digging is impractical.”

Now we’ve got a serious problem.  This practice is recommended for existing beds.  Not only will extensive digging or rototilling destroy any soil structure you might have, it will also take out the roots of any desirable plants in the vicinity).

But let’s continue to ignore reality and go on to the annual recommendations for adding compost to soils.
“Clay soils: 16 cu. feet (.6 cu. yard) = 2 inch layer of compost for new gardens. Use 1 inch per year in established gardens.”
“Sandy soils: 24 cu. feet (.9 cu. yard) = 3 inch layer of compost for new gardens. Use 1 – 2 inches per year in established gardens.”

Is the compost used as a mulch in these existing gardens?  No – the guidelines are prefaced with this instruction:  “Gardens: mix compost to 10- to 12-inch depth.”  (Can’t say this does much for promoting root growth either.)

This document shows a breathtaking lack of understanding of how landscapes function, especially over the long term.  It takes an agricultural practice (annual organic amendment of crop fields) and misapplies it to permanent landscapes.  It is devoid of the research which continues to show that improper soil amendment can cause serious problems such as soil subsidence, perched water tables, and nutrient overloads.  This last point is especially important to anyone living near aquatic ecosystems, since excess nutrients always end up in the water.

Before you plant this year, find out what your soil needs before amending it.  And remember that mulching is the natural (and sustainable) way to add organic matter to the soil.

International Ag Labs – who are they and what do they do?

Last week I posted a short message about this company, asking you to do a little homework.  Bryn, CP, and Karen all have teased out some details that agree with my skepticism on how reliable this company is for soil testing and analysis.  (See last Wednesday’s post and comments if you haven’t read them already.)

To back up a little bit, I received an email from LB last week, along with the attached soil test, analysis and recommendations. LB intends to do some “market gardening” and here are his questions:

1. Is there anything to this perspective? Understanding your soil and rl37 (a “Jack of all trades” product).

2. I “get” that I should not willy nilly spread compost over everything, but what in the attached recommendation (based on the soil analysis) should I follow (Note: Crescendo and Stimulate are no longer offered, but there are lots of other interesting products here.)

3. Have you read any peer reviewed research that supports their “High Brix” market garden approach that uses sugar content and refractive index to supposedly correlate to improved flavor and higher nutrient content in selected vegetables?  I have heard of chefs using this to evaluate certain produce (carrots and tomatoes) in the market but nothing in a peer reviewed journal.”

Take a look at the linked report from IAL (from the second paragraph).  This is a confusing analysis, as it combines traditional ppm measures with pounds/acre.  (My understanding is that you can divide this latter number by 2 to get ppm.)  However, pounds/acre only represents a portion of what’s actually available in the soil.  It’s not an indication of how much, if any, of these nutrients to add.  (If you’ve never seen U. Mass Amherst’s soil testing lab, take a look at their webpage, especially their fact sheets related to soil testing.)

What irks me is the recommendations (which are in the first table in the attached document).  I’m not even sure of the rate – I assume it’s per acre, but who knows? And what is the purpose of all this stuff?

This company is heavily used by many people, including researchers (if you Google the name of the company along with site:.edu, you’ll find reference to articles and university reports that use their services.

Let’s have some discussion on this.  I’m certainly not an expert on performing soil tests, but I’ve had enough of them done that I have a pretty good idea how to interpret them and their recommendations.