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by paul wheaton

Soil pH stuff

This one little thing costs almost nothing and can make such a huge difference in the health of your soil. There are people that just buy a bag of lime every spring for $2.50 and spread it evenly over their lawn. They have great results. And lots of people in the same area do the same thing and have equally great results! And if you tried to do the same thing, it could kill your lawn and feed the weeds!

The key to being cheap and lazy is to use your brain more than your wallet or your sweat. On the other hand, learning all this stuff can take a lot of time! So I'm going to try and spell out a recipe for adjusting your pH while leaving out about a dozen textbooks of information.

first: have your pH professionally tested!

Without knowing the current pH of your soil, you run the risk of making things worse!

Testing pH is real science. And nearly all of the products available on the shelves of your local gardening supply are crap. They can be (and in my experience, usually are) off by so much that the prescribed treatment can kill your lawn. The most basic pH meters that will do any good start at about $65. Then you need calibration solutions and you need to know how to use them.

When I lived in Missoula, Montana, you could take a soil sample into the local extension office and they would test your pH for free. But I have since learned that most extension offices don't do that. Instead, they give you a form to fill out and send to some lab along with a check and a soil sample.

I've sent soil samples to labs in the past. About $35 and I get back not only pH, but all sorts of other info. Pretty cool for those of us that are into that sort of thing. But most people probably don't want to shell out that much money and wouldn't make heads or tails of the data that came back anyway.

You can test any time of year that your soil is not frozen. Wet or dry is fine.

You will need about two tablespoons of soil in a ziplock bag. Do not use the top inch of soil in your sample - scrape that away first. Then collect soil from one inch deep to about four inches deep. I usually mix the soil from about three different spots. And then send in four samples at once. In other words, I'll send in four little ziplock bags ... one bag might be labeled "west yard" and will contain a bit of soil from three different places in the west yard. Another bag might be labeled "south garden" and have some soil from three different places in the garden.

A lovely list of soil testing labs is here.

Adjust your pH

If your pH is 6.2 to 6.9, relax and forget about it! Grass favors a pH of about 6.5 - and you are in the zone!

If your pH is 5.9 to 6.1 or 7.0 to 7.2, adjusting the pH will noticably help, but I would be powerfully tempted to let it go.

This is a good time to point out that compost is the great neutralizer. No matter what your current pH, compost brings your pH closer to optimal. Compost also brings more nutrients, and more nutrient parking spaces. It provides food for earthworms and all sorts of microbial life. This is the closest thing to a magic bullet you can find! But .... unless you make it yourself, it will cost you. And the stuff available for sale is usually loaded with some undesirable stuff too. Most commercial compost is made from somebody else's industrial waste (usually wood chips and feed lot manure, but there are cases of some really icky stuff getting into commercial compost).

All the compost I make goes for my garden. Once in a while I might use a little on my lawn. Unless the grass is really pathetic, it's just too expensive to add commercial compost.

As an alternative, I try to feed the soil that feeds the grass and the grass clippings fall between the living blades of grass to provide this compost-like organic matter. The worms will move the old grass blades down into the soil. The cheap and lazy way to grow my own compost this way is to fertilize and make sure my pH is good.

When trying to change the pH of your soil, you will add something - generally to the surface of the soil. How much to add and which something to add depends on loads of things. For example, suppose your pH is 5.5. And you are going to raise your pH using lime. If you are going to till it in, you would add 45 pounds of lime to 1000 square feet if your soil is almost pure sand. If your soil is almost pure clay, you would need to add more than twice that much to get the same result! But you probably aren't going to till it in. So now your soil surface has a pH that can be so high it is toxic to your grass, and the soil a few inches down is still too low! This is where a spreader can be used to try and get the amount of lime laid down spread really evenly so that you don't make toxic spots. But buying or renting a spreader can push you out of the world of "the cheap and lazy."

So I'm going to assume you have no idea if your soil is clay or sand. And that you don't want to mess around with a spreader. I'm also going to assume that you want to do this on the cheap. So the following recipes are going to "play it safe." Money and effort is replaced with patience. Rather than tilling in the perfect amount of cure, we're going to take it easy, get some help from earthworms, and figure that the lawn will be optimal in a few years if we don't get it spot on the first year.

Do not apply ammendments when your lawn is dormant (too cold or too hot). After ammending your soil, wait at least two months and then re-test your soil.

pH	What to do
6.0	Apply 20 pounds of lime per 1000 square feet
5.5	Apply 25 pounds of lime per 1000 square feet. At least a month later, add another 20 pounds of lime per square feet.
5.0	Apply 25 pounds of lime per 1000 square feet. At least a month later, add another 20 pounds of lime per square feet. Wait at least another month and then add another 20 pounds of lime per square feet.
4.5	Apply 25 pounds of lime per 1000 square feet. At least a month later, add another 20 pounds of lime per square feet. Wait at least another month and then add another 20 pounds of lime per square feet. Wait at least one more month and then add another 20 pounds of lime per square feet.




pH	What to do
7.5	Apply 10 pounds of gardener's sulfur per 1000 square feet
8.0	Apply 20 pounds of gardener's sulfur per 1000 square feet
8.5	Apply 40 pounds of gardener's sulfur per 1000 square feet

Other nutty tidbits about pH

Wood ashes have a high pH. If you burned really clean wood (no paint or funky chemically stuff) you can dust your lawn with wood ashes once in a while to help raise the pH. Just make sure you don't let it clump!

Peat moss has a pH of about 4.5. But go easy with this stuff. It's also pure organic matter. Unfortunately, it has some strange properties that make it so that you wouldn't want to put it on top of your lawn without mixing it with some compost. I've seen some lawn disasters that included putting peat moss on the surface.

Conifers (pine tree, cedar trees, fir trees, etc. - trees with needles) love a very acidic soil. You don't have to make the soil acidic for a conifer - it will do that by iteself! This is why so few things will grow under a conifer: the tree dropped loads of acidic needles there! Since blueberries love an acid soil, you can often find blueberries growing under conifers. In Montana, "huckleberries" are actually blueberries growing wild under conifers!

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Here is an interesting tidbit. Your soil could be loaded with nutrients, but when the pH is off - some of those nutrients become unavailable:


(from Colorado State University Cooperative Extension)

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About ten years ago I read a small mountain of books on edible gardening and I took some pretty good notes. For any book that mentioned pH, I wrote down the numbers for the plants I was interested in. So my notes for beans looks like this: "5.5 to 7.0, 6.4, 6 to 7.5, 5.5 to 6.5, 6.0 to 7.5, 5.4 to 6.9, 6.0 to 6.8, 5.5 to 6.8, 5.0 to 6.5". Later I made a note to the side of the agreed upon range ("6.0 to 6.5").

So here is my summary:

plant	common pH range
beans	Tossing out one rangless reference (6.4): 6.0 to 6.5
broccoli	6.5 to 6.8
carrots	5.8 to 6.5
corn	6.0 to 6.5
garlic	5.5 to 6.8
lettuce	6.5 to 6.8
onions	6.5 to 6.7
peas	6.0 to 6.5
peppers	5.5 to 6.5
potatoes	5.0 to 5.4
pumpkins	One book had a range outside of the ranges of all the others, so there is no common range. But if I throw that one out (5.0 to 5.5), then the common space for the other seven is 6.0 to 6.5
radishes	6.0 to 6.5
raspberries	raw data: 5.5 to 6.8, 5.5 to 7.0 and 5.0 to 5.5. So perhaps the optimal pH is 5.5?
rhubarb	5.9 to 6.5
strawberries	5.8 to 6.5
tomatoes	Lots of ranges including 6.5. One range of 6.5 to 7 and another of 5.6 to 6.5 makes the final value 6.5.

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