It takes a surprisingly small depth of fall leaf litter to provide an adequate supply some key nutrients for your vegetable garden. Leaves-as-fertilizer is just another reason to #leavetheleaves.
A time to plant garlic, and a time to refrain from planting garlic.
It may be difficult to believe, but some versions of the Bible actually omit that line from Ecclesiastes 3.1-11.
I’m getting ready to plant a 4′ x 8′ area with hard-neck garlic, for harvest next year. Plant the cloves in the fall, once the soil is good and cold, and, with any luck, they’ll come up next spring and give you nice big heads of garlic by mid-summer. I wouldn’t know, because, typically, I plant them too early, by contrast, and they’ll sprout now. They may survive into next year, but I can tell you from experience, the result will be puny, unusable heads of garlic.
(Weird garlic fact: If you plant bigger cloves, of a given variety, you’ll harvest bigger heads of garlic. I’ve seen this result replicated enough times that I’m fairly certain it’s true. E.g., Red Gardens stumbled across this effect, but you can find it in many scholarly sources as well. This is arguably the only reason not to plant grocery-store garlic. As it turns out, “culinary grade” garlic, found in the grocery store, has smaller cloves than the garlic reserved to become “garlic seed”.)
Two options for Nitrogen fertilizer
The lowest recommended fertilizer application I found, for commercial garlic growing, was from Cornell University. Their most recent study said that that 50 pounds of nitrogen per acre would be sufficient, and that yields did not increase if you added more than that. Essentially, you should expect your garlic to pull that much nitrogen out of the soil, so that’s what you need to replace.
I could supply this using 30-0-0- lawn fertilizer. To be clear, I think that putting lawn fertilizer on your lawn is crazy and environmentally destructive. But it’s a good source of nitrogen. I own a 10-pound bag of it. I’ve owned that particular bag for maybe a couple of decades now.
To supply the complete nitrogen needs of by 4’x8′ garlic bed, I would need four level tablespoons of lawn fertilizer. Like so:
If nothing else, this shows you why you shouldn’t just wing it, when it comes to concentrated chemical fertilizers. You only need trace amounts. That’s such a small quantity of material that it would be difficult to spread that evenly over the bed.
But, in fact, I’m going to supply this using fallen leaves. Because a) why not, and b) the leaves serve as both mulch (before they decompose) and fertilizer (after they decompose).
How deeply must I bury that bed in fallen leaves, to supply all the nitrogen the garlic requires? Take a guess:
- An impractically large layer (e.g. feet of depth).
- An inconveniently large layer (e.g., one foot of depth).
- A few inches of leaves.
The answer is C, a few inches. In this exact calculation, the answer is that about half-an-inch of fallen leaves should be adequate. Surprise. That’s based on leaf litter containing about 1% nitrogen by weight, as shown here.
To double-check that, I can start from an alternative data source. At a mean of 10 grams of nitrogen per kilogram of leaves, I would need about 1.5 kilograms, or maybe 3.5 pounds of leaves, to supply the required nitrogen. Same as the calculation above.
Source: American Journal of Horticultural Science.
Unlike the water-soluble lawn fertilizer, where excess will run off with the rainfall, it’s probably close to harmless to err on the upside with leaves. Some sources suggest fertilizing at up to three times the rate recommended by Cornell. And, to be sure, the actual N content of my particular leaves might be less than average. And maybe there’s some catch here, such as the N in fallen leaves being less readily available than the N in commercial fertilizer. So, in theory, if I wanted some insurance, I could pile (say) three inches of leaves on that garden bed let them rot over the winter.
The term of art for this — for letting a relatively thin layer of leaves rot over a large area — is sheet composting. By calculation, I can easily supply the required nitrogen for my garlic by sheet composting my fallen tree leaves on that bed.
In fact, fall leaf litter contains so much nutrient, in total, that in well-watered climates, centralized leaf collection reduces nutrient runoff into the surrounding surface water. So says the USGS, in this piece. I count that as the sole potential environmental benefit of centralized leaf collection.
During the growing season, it’s better to compost the leaves first, then add that to the bed. The act of breaking down the leaves temporarily draws nitrogen out of the very top layer of the soil (explained per this reference). But by the time the garlic needs nitrogen in the spring and summer, that thin layer of leaves will have already broken down.
Like sulfur for garlic?
Finally, this year, I’m going to give my garlic a little sulfur. If I can figure out how to do it.
It seems like a not-unreasonable thing to do.
First, sulfur is a key component of allicin, the chemical that makes garlic, garlic. Some research suggests that sulfur-deficient soil results in garlic with less allicin, which I think has to mean, less garlic-y. And, possibly, smaller bulbs, to boot. I see no point in growing small, bland garlic bulbs.
For sure, garlic withdraws sulfur from the soil. Whether or not the soil is actually deficient, it seems prudent to put the expected amount of the sulfur withdrawal into the soil head of time.
By my estimate, if all goes well, I’ll need to replace about a gram of sulfur per square foot of garlic bed. Or, in this case, 32 grams of sulfur, just bit over an ounce of weight, in the 4’x8′ bed I’m planning to use. That’s assuming I get lots of garlic out of this patch, two 100-gram bulbs per square foot. More realistically, this is an upper bound on what I need.
The hard number is that garlic is about 0.5 percent sulfur, by weight (this reference). The naive assumption is that I can grow 6400 grams of garlic in 32 square feet of bed. (Then 0.5% of 6400 = 32 grams). That seems to ballpark with other published estimates.
Can I do this with Espoma Holly-Tone? Maybe.
Source: Espoma.com, used without permission.
Turns out, I own a big, almost-unused bag of Espoma Holly Tone. Why, I cannot recall.
Which probably explains why the full bag is still here. It’s a result of a reverse-Darwinism, survival-of-the-un-fittest process. If the duds are allowed to linger, they eventually dominate fill your storage space, for the simple reason that they don’t get used. Likely, whatever I bought this for, long ago, did not pan out.
Will it work here, to give me my 32 grams of sulfur? Because I sure won’t mind using some of that up. To get 32 grams of sulfur, I need about a pound and a half of Espoma Holly Tone.
That seems like a lot, and that’s a problem. If I do that, I add too much nitrogen. The Espoma mix is 4% N. When I do the math, that 1.5 pounds of Espoma H-T- provides 0.06 pounds of N, or about twice what the Cornell-derived estimate suggests that the garlic needs.
Given that I am going to cover this bed in fall leaves, I may have to buy something else for sulfur. Looks like the Espoma H-T can provide enough sulfur, but it brings along too much N (etc.) that I’d rather provide by sheet-composting leaves.
Maybe a reduced amount is called for. Maybe some different product entirely. We’ll see. There are still things about sulfur as a soil amendment that I clearly do not yet grasp.
Finally, I have to find a cheap test for soil sulfur, if such exists. For now, I’m still feeling my way through the whole sulfur-for-garlic thing.
Conclusion.
Am I going to rake my leaves to the curb this year, for vacuum pickup by the Town of Vienna. No.
Do I need to add chemical fertilizers to my spring garden? No.
Are those flip sides of the same coin? Yes.
Add sulfur to garlic bed? Not clear yet.
