Knock It Off – Page 9 – The Garden Professors™

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.

Mouse Tombstones

Doing this…

I must identify each and every Wave petunia!

leads to this…

and this…

Unfortunately, the second and third photo are from a college teaching and display garden. There are a lot of inexpensive yet more attractive ways to relate plant identification to your visitors.

We all do this, of course, to some extent in our home gardens. Walk around with weird plant in hand, dig hole, stick it in, say to self "I’ll come back and get that label to add to my (pick one) Excel garden database/bag of random tags/photographic memory."

Typically, most of mine end up on top of the washing machine from cleaning out pants pockets. Not exactly a good record-keeping system.

Tags as tombstones: during spring mulching, I’ll typically find a few half-buried, printed with, oh, Maybehardii maybenotus – Plant Delights Nursery $25. Said plant is nowhere to be seen. Dang.

A salt bath for your tomatoes?

This morning I got an email from one of my gardening colleagues, wondering about the wisdom of watering tomato plants with salt water. He had a link to a UC Davis website which tacitly endorses spraying tomato plants with 10% salt water “to increase their nutritional value and taste.” Unreferenced “worldwide studies” are mentioned, along with the “major potential benefit of providing irrigation for crops in areas with freshwater restrictions.”

Before we deal with the impracticalities and out-and-out harm of using salt water for irrigation, let’s look at why this practice would work on tomatoes. By training I’m a plant stress physiologist (and I’m well versed in the primary literature on this topic). Watering tomato plants with a salt solution imposes a drought stress on the entire plant, as less water is taken up under these conditions. So leaves and fruits are smaller and they may produce stress-induced biochemical compounds in response. The upshot is that you have smaller tomatoes with a higher concentration of various solutes, some of which might be tastier or more beneficial to humans.

Guess what? You can do the same thing by decreasing irrigation during fruit set! Less water means smaller fruit and increased concentrations of sugars and other plant compounds, and voila! So you can skip that step of adding salt water and just cut back on irrigation to induce a mild drought stress.

So…why in the world would you dump salt water on your garden soil? The article blithely dismisses this: “Many are still concerned about salt causing soil degradation and rendering some seawater-treated tomatoes inedible, but scientists cite that plants thrive in balanced soil containing both macro- and micronutrients.” Sorry, but sodium is NOT a micronutrient for most plants and does NOT contribute to a “balanced soil” in one’s vegetable garden.

An ironic twist to this whole article is that most of the research that’s been done is relevant to arid parts of the world (the Middle East, primarily) where saline soil conditions and limited water are common. I can’t imagine what they would think about people who would deliberately contaminate good soil by adding salt water to it.

Parking tickets, compost tea, and pseudoscience in the Ivory Tower

Back in November 2009, Jeff posted an educational and amusing commentary about Harvard’s use of compost tea. Much vigorous discussion followed, and we’ll return to that topic in a moment. But first, I’d like to tell you about my morning yesterday.

In September of 2010, I received a ticket for parking longer than 2 hours in a restricted zone. Now, there was no way I committed this infraction; I had hard core proof that could not be rationally challenged. So, armed with my husband’s affidavit as to my whereabouts, as well as a dated receipt showing I was at the post office at the time when I was apparently parked several miles away, I went to court to challenge the ticket. During our briefing, the sitting magistrate told us we would need to provide a “preponderance of the evidence” to win our respective cases. For me, it was an anticlimactic turn of events, as the citing officer (whom I’d subpoenaed) did not show up, so the ticket was dismissed for lack of evidence.

And thus we return to today’s subject – use of compost tea without a “preponderance of the evidence.” Jeff took Harvard to task for buying into this “bullpucky”, I think he called it, and now Berkeley has decided to drink the Kool-Aid. One of my dear colleagues at University of Washington forwarded me a link announcing that Berkeley Botanic Gardens was adopting compost tea as an “eco-friendly fertilizing method.”

As the article reports, compost tea is being used

1) as a disease suppressant
2) to provide nutrients, and
3) to reduce the amount of water needed.

I’ve written a lot about compost tea, and I’ve reviewed journal papers on the topic as well. In a scientific nutshell, there is no solid evidence to support use of compost tea, particularly aerated compost tea, in disease suppression. Likewise, there is no evidence to support a nutritional role (I just finished reviewing a manuscript on this topic and the data were unconvincing). Finally, I cannot understand why spraying compost tea onto the leaves of a plant would reduce its water requirements. The “preponderance of evidence” is truly lacking.

Students at Berkeley have the dubious honor of supporting this nonsense through their student fees: $11,000 has been spent on a 300 gallon tank, worm composting bins, and a spray tank.

Whatever happened to using good old compost, and letting nature create its own “tea?” (Compost used as a mulch also helps reduce irrigation needs.)

Tree terrors continue

You might remember back in October 2009 I gave one of the first Friday quizzes. The featured tree had epicormic shoots, and Monday’s answer revealed the neglected wire staking that was slowly girdling the main trunk. (Be sure you click on those links to see what the tree looked liked in 2009.)

I thought you might be interested to see what this tree looks like now:

A picture is worth a thousand words….many of those unprintable.

Update January 2022 – in response to a reader question, here is the tree in 2019 thanks to Google maps.

Unspeakeable Acts of Pruning

(Hey, I think it’s Tree Week on the GP!)

Our land has a nice buffer of big, old oaks, hickories, and maples between us and the two-lane highway. Power and phone lines thread through the middle of them. Thus, I have nightmares about orange Asplundh trucks.

So with much concern, I noted that utility crews and
subcontractors have been out in full force in our rural area,
inexplicably leaving one tree and then “pruning” another.

OMG that's awful

I pulled over and snapped this latest atrocity last night. The power lines are to the right (not in photo). As this is only a mere mile or two from our property, I may sit at home on the porch next week with the shotgun in my lap.

Guano

One of the best organic fertilizers out there – at least in terms of how plants respond to it — is bat guano. As most of you probably already know, bat guano is made of bat droppings. What you probably don’t realize is that bat droppings need to be aged for a while in an arid environment before they become guano. Caves provide the perfect environment for this to occur, and so that is where most bat guano comes from.

Because guano needs to be aged in special surroundings before it is used it is not a rapidly renewable resource. Instead it’s kind of like peat in that it takes anywhere between decades and thousands of years for the raw material from which it is made to develop into the stuff that we use. Furthermore, by harvesting bat guano we can actually damage the ecosystems present in the caves from which the bat guano is harvested. Think about it – bats generally feed outside the cave, so when they defecate inside the cave they are actually bringing new nutrients into the cave – nutrients that other creatures can use. Whole ecosystems are based on this poo! So when we harvest bat guano from a cave what we are doing is disturbing a specialized ecosystem – a very unique system.

So am I encouraging you away from bat guano? No more than I would encourage you to consider reducing your usage of peat – or of oil — or any other non-renewable resource. I can’t deny that it’s a great fertilizer, but if you want to use an organic fertilizer why not at least consider one that is renewable instead of one that is from a limited resource and which may cause harm to a unique ecological system?

Planting trouble: multiple trees in one hole

[I enjoyed Jeff’s Valentine story so much that I thought I’d stick to the theme of togetherness…for better or worse.]

A week or so ago a reader asked about the practice of planting three or four fruit trees in the same hole. Having not heard of this before, I checked on the web and found many “how to” pages geared to home gardeners who either want a longer harvest of a particular fruit (early to late) or a mixture of different species. Doesn’t it sound just great, especially for smaller urban yards?

One of these sites has these written instructions: “Plant each grouping of 3 or 4 trees in one hole at least 12 to 15 inches apart.”

Now, I’m sorry, but this is just asking for trouble down the road. Readers of this blog know that root systems extend far past the drip line, and that roots from different trees are going to compete with one another. You’ll end up with three unhappy trees, all jostling for space and resources, just like kids in the back seat during those long car rides.

But wait! you might say. There’s research on high density tree planting, and it’s been shown to increase fruit yield on a per acre basis!

Yes, in fact there is a lot of planting density research on many different species of fruit trees. What’s considered by researchers to be “high density” varies, but it rarely exceeds 2698 trees/acre (6666/ha for our international readers). Optimal and sustainable levels of high density planting are also variable, as they depend on not only species but rootstock and the crown architecture; 1214/acre (3000/ha) might be a mid-range number. This can be converted to a per-tree requirement of 36 sq. ft. or a 6’x6’ planting area.

How does this compare to the 12-15” recommendation given earlier? If we’re generous and use the 15” recommendation, this translates to 6.25 sq. ft. per tree or 6970 trees/acre. The 12” recommendation would lead to a whopping equivalent of 10,890 trees/acre. (And no, it doesn’t matter if you’re using dwarfing rootstock or not; most of the higher densities in the literature are for dwarfing rootstocks.)

You don’t have to be a math whiz to see that these densities are totally out of line with reality. Sure, you can probably keep overcrowded trees alive with lots of water and fertilizer, but they’ll be under enough chronic stress so that pests and disease might take hold, and fruit production will likely be poor. And it’s about as far from a sustainable practice as you can get.

Fast food is unhealthy for plants, too

In early December, I posted my thoughts about fertilizing crops vs. landscapes. An anonymous reader asked if we could follow up by discussing the relationship between excessive fertilizers and plant susceptibility to pests and disease. It’s taken a month to get the scientific literature (and my act) together, but here it is.

There are decades’ worth of articles about the direct relationship between increased nutrient availability and increased susceptibility to pests, disease, and disorders. One of the earliest articles linked the incidence of celery blackheart to over-fertilization. Since that time, researchers have found similar causal relationships in vegetable crops such as rice, onions, and soybeans, ornamental crops including poppies, and perennial orchard crops such as nectarines. Unfortunately, there’s been no research on landscape species.

Happily, the way plants react to excess nutrient levels is generic – so we can apply the findings in the agricultural literature to landscape situations. Just like kids and candy, plants will greedily take up all the available macronutrients their roots can find, especially nitrogen and phosphorus. (It makes NO difference is the fertilizer is organic or inorganic.) Plants in highly nutritive soils respond with lush vegetative growth – and fewer flowers, by way. Less metabolic energy is put into protective compounds, so these succulent new leaves and shoots are prime targets for all kinds of unwanted plant-eaters and foliar pathogens.

As with so many things in life, moderation is the key. For routine landscape needs, use woody mulches rather than fertilizers and nitrogen-rich composts. This “slow food” approach not only benefits your plants, but provides ideal habitat for mycorrhizal species, which have been shown to help restrict root uptake of excessive nutrients, while assisting with uptake of less available ones.

Organic Honey?

As there seems to be a good deal of interest in the topic of honeybees, and I’m a beekeeper, albeit relatively novice, I thought I might continue a bit of discussion.

I’ve been beekeeping for three years, and I sold my first honey harvest this fall. Six gallons, divided into pint and half pint-sized jars. As a newbie, extracting the honey from the frames and getting it into the jars was, by far, the messiest thing I’ve ever done. It’s like wrestling with a living thing…the garage and kitchen still have sticky spots. It also took forever – honey moves through a three- pail, three-filter system (eventually removing particles down to 200 microns) like…cold molasses. Once it was properly subdued and contained, I looked into what was required for labeling. Very interesting. And very, very, vague.

Honeybees have been described as “flying dust mops” – there is no way, unless the beekeeper owns all the land in a several-mile radius, that one knows what they’re getting into. Our girls’ primary duty is pollination of our four+ acres of blueberries, so their primary pollen and nectar source in late spring is our four acres of blueberries. After that, they hit the sourwood, wingstem, mountain mint, and the smorgasbord of of perennials and annuals in the garden borders. We don’t use any pesticides on our farm (the cabbage looper and stink bug invasion this year is really testing me on that one). But that doesn’t mean the gentleman next door isn’t using Sevin on his squash or pyrethrins on his potatoes. And our bees are just as likely to be over at his house as ours (despite my stern lecture to them).

Noticing the honey labeled “USDA Certified Organic” sold for a premium at both my local grocer and favorite “natural foods” store, I spent some time digging as to certification standards, and whether it would be worth it to get certified.

I came up fairly empty-handed. There does not seem to be any USDA National Organic Program certification standards for honey. Apparently there are some trade-law guidelines that allow honey to be imported from Canada and Central/South America labeled as USDA organic. Very confusing, and very weird. But apparently some U.S. honey producers, both large and small, have gone ahead and slapped USDA Organic labels on anyway. Along with other meaningless statements like “Superior grade” or “All natural”. Some states such as Pennsylvania are pushing for NOP standards, noting their beekeepers are at a disadvantage, marketing-wise, if they cannot certify their honey but Canadian or Argentine producers can. On another front, beeswax, especially older wax in frames that are in brood hives for several years, can accumulate pesticides brought in from foraging bees like nobody’s business. So I’d also look askance at claims of products containing “organic beeswax.”