Your Soil Needs a Test and Compost, Not Another Bag of Fertilizer

Quick answer: Mail a soil sample to your state's cooperative extension lab this fall. Then spread an inch of compost on top of your beds every year, and stop buying fertilizer the test didn't ask for.

The most common thing wrong with a home vegetable garden isn't bugs or weather. It's a guy standing in a garden center aisle holding a bag of 10-10-10 because his plants looked a little yellow and the bag had a picture of a tomato on it.

Sometimes that works. More often he's dumping phosphorus into a bed that already has plenty, the real problem is a pH of 5.4, and the leaves stay yellow. He fed the plant. The plant was never the problem.

The ground was.

Spend twenty dollars before you spend two hundred

Every state has a land-grant university with a cooperative extension service, and nearly all of them run a soil lab or will point you to one. A basic test usually runs somewhere around $15 to $30. You get pH, phosphorus, potassium, often organic matter, and a written recommendation for the crop you name on the form. It's the best money you'll spend in the garden all year.

A sample is only as good as how you pull it:

• Use a clean trowel and a plastic bucket. Galvanized buckets can throw off the zinc reading.
• Dig 6 inches down in eight to ten spots across the bed and keep a thin slice from each.
• Mix it all together, let it air-dry on newspaper, and send the amount the lab asks for.
• Sample the lawn and the garden separately. The bed by the downspout gets its own bag too.

Do it in fall. Labs are buried in April, and if the results say lime, lime needs months to shift pH. Spread it in October and it's working by planting time. Spread it in May and you've just done next year's job.

Most vegetables want a pH between 6.0 and 7.0. Blueberries want something closer to 4.5 to 5.5, which is why they sulk when you plant them next to the peppers.

Find out what you're actually standing on

The test gives you chemistry. It won't tell you texture, and texture decides how your ground drains and holds water. A quart jar will.

Fill it a third of the way with soil from the bed, top it with water, add a drop of dish soap, and shake it hard for a couple of minutes. Set it on the windowsill. Sand drops out in about a minute. Silt settles over a few hours. Clay can take a day or more to clear. Mark each layer on the glass and you've got your ratio.

Heavy clay holds nutrients well, drains badly, cracks open in August and turns to glue in a wet spring. Sandy soil drains in minutes and holds nothing. Silt sits in between and packs down if you walk on it.

The fix for all three is the same. That's the best news in gardening.

Compost answers almost every question

Organic matter makes clay crumble and makes sand hang onto water. It feeds the fungi, bacteria and worms that do the real work of turning nutrients into something a root can use. Fertilizer is a meal. Compost is the kitchen.

Finished compost is dark and crumbly, smells like a forest floor after rain, and you can't tell what it used to be. If you can still pick out banana peels, it isn't done. If it smells like ammonia or a dumpster, you've got too many greens and not enough browns. The fix for that, and for keeping the raccoons out of it, is in Compost That Doesn't Stink or Feed the Rats.

Then leave it on top. One inch a year spread over the surface, in fall or early spring. The worms will pull it down for you. They work cheaper than you do.

How much you need

An inch of compost over a 4x8 bed comes to about 2.7 cubic feet. Three one-cubic-foot bags and you're done. If you're starting from bare ground, Build a 4x8 Raised Bed for Under Two Hundred Dollars covers the frame and the fill.

Past a couple of beds, bags get silly. A cubic yard is 27 cubic feet and covers about 324 square feet an inch deep. Most areas have a landscape supply yard that sells compost by the yard, and plenty of towns sell or give away compost made from fall leaf pickup. Call around before you load forty bags into a cart. Prices swing too much by region to quote one, but bulk almost always wins once you're past a few beds. Compost is light, so a full-size pickup will haul a yard without complaining. Just ask what the delivery fee is if you don't have the truck.

What goes wrong

Free manure that kills your tomatoes. A few broadleaf herbicides used on hay fields and pastures, mainly aminopyralid and clopyralid, can pass through horses and cattle and survive composting. Spread that manure and your tomatoes, beans and peppers come up with cupped, twisted leaves. Corn and grass shrug it off, which makes it maddening to diagnose. Before you take a truckload from a farm, ask what the animals ate and whether the hay was sprayed. If nobody knows, plant a few bean seeds in pots of the manure mixed with potting mix and a few in plain potting mix. If the manure pots come up curled, walk away.

Fresh manure, period. It can burn young roots and carry E. coli. Compost it first. If you use it raw anyway, the USDA's organic program sets a floor: at least 120 days before harvest for crops whose edible part touches the soil, 90 days for the rest.

Too much of a good thing. Gardens fed heavy compost and manure for years often test sky-high in phosphorus. More won't help, and the excess washes off into creeks. One more reason to retest every few years instead of piling on by habit.

Wood chips dug in. Chips on the paths or as surface mulch are great. Tilled into the bed, they make the microbes grab nitrogen to break them down, and your plants go pale. Keep them on top.

Bagged "garden soil." Quality is all over the map. Some of it is mostly ground bark. Open one and squeeze a handful. If it looks like mulch, that's because it is.

Put the tiller in the back of the shed

Tilling every spring feels like work, so it feels like progress. It breaks up the soil's structure, burns through organic matter faster, and drags buried weed seeds up into the sunlight where they've been waiting for you.

Fair concession: if you're breaking new sod or fighting compacted clay the first year, a rented tiller earns its money. After that, let the ground be. Add compost on top, mulch, and pull or cut weeds at the soil line. If the soil needs loosening, a broadfork opens it up without flipping it over.

When a crop is finished, cut it off at the soil surface and leave the roots. They rot in place and leave channels for water and air.

Bare ground over winter is wasted ground. In colder zones, cereal rye sown in early fall holds the soil and comes back green in March. Where winters are milder, crimson clover pulls nitrogen out of the air for next year's crops. In hot climates, buckwheat or cowpeas fill the summer gap when it's too hot to grow much else.

Your zone sets the calendar

For most of the country, fall is soil season. Leaves are free, lime has time to work, and you aren't racing the planting date. In the Deep South and the low desert, fall is planting season, so do your amending in late summer instead. If you don't know your number, Your Hardiness Zone Decides What Lives and What Dies sorts it out.

Out West, a lot of soil runs alkaline, with a pH above 7.5. There the fix is sulfur, not lime. Don't lime by habit because your dad did it back in Ohio. Test first.

And if you rent, or you're working beds somebody else dug before you, the old rule still holds. Hand the ground back darker and looser than you got it. Whoever gardens there next won't know your name.

Their tomatoes will.