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Growing & Soil

How to Test Your Soil (Without a Lab, and With One)

Your soil is the whole game. Here's how I read it by hand, what a real lab test tells you, and how to fix what you find — the way I do it here in El Campo.

J By Jordan Polasek · 9 min read · El Campo, TX
How to Test Your Soil (Without a Lab, and With One) illustration

Everything I sell starts with soil, so this is the first thing I'd want you to understand. You can buy the best seed in the world and it'll still sulk in dead dirt. The good news is you can learn most of what you need to know about your ground with your hands and a jar before you ever spend a dollar on a test.

The jar test — texture in an afternoon

Soil texture is the ratio of sand, silt, and clay. It decides how your soil drains, how it holds nutrients, and how often you'll be watering. You can measure it with a mason jar.

1

Fill a third

Put about a third of a quart jar full of soil from a few inches down. Pull out rocks and roots.

2

Top with water

Fill nearly to the top with water, add a teaspoon of dish soap to break up clumps.

3

Shake hard

Shake it for two full minutes until everything is suspended.

4

Let it settle

Sand drops in a minute, silt over a couple hours, clay over a day or two. Mark each layer.

Measure the layers. Mostly sand drains fast and dries out — great for rosemary, hard on lettuce. Heavy clay holds water and nutrients but compacts and drowns roots. The sweet spot most vegetables want is loam: roughly 40% sand, 40% silt, 20% clay. Around here on the Gulf Coast you'll often find heavy clay, which is why I grow so much in raised beds and cloth pots.

Reading soil by feel and color

Grab a handful of damp soil and squeeze. If it ribbons out between your thumb and finger like clay on a wheel, you've got clay. If it falls apart no matter what, it's sandy. If it forms a loose ball that crumbles when poked, that's loam — what you're after.

Color tells you about organic matter. Dark, near-black soil is rich in it. Pale, grayish, or yellow soil is hungry. The smell matters too: living soil smells sweet and earthy. Sour or chemical smells mean poor drainage and anaerobic conditions.

The pH test, and why it matters more than fertilizer

pH controls whether nutrients are even available to roots. You can pour all the fertilizer you want on soil that's too acidic or alkaline and the plant still can't take it up. Most vegetables want a pH between 6.0 and 7.0. A cheap probe or a packet of test strips from any garden store gets you close.

ResultWhat it meansHow I fix it
Below 6.0 (acidic)Common in high-rainfall areasGarden lime, worked in over a season
6.0–7.0The target for most vegetablesMaintain with compost
Above 7.5 (alkaline)Common in arid/limestone soilsElemental sulfur, peat, acidifying compost

When to spring for a real lab test

A mail-in lab test from your state extension office is cheap — often under $20 — and worth it before you build a big garden or buy land. It tells you exact nutrient levels (nitrogen, phosphorus, potassium), pH, organic matter percentage, and often a recommendation tailored to what you want to grow. In Texas, the Texas A&M AgriLife Extension soil lab does this. Take samples from several spots, mix them, and send a cup.

Jordan’s tipSample at the same depth you'll be planting roots — about 6 inches for vegetables. One sample from one hole isn't representative; walk a zigzag across the plot and combine a dozen small scoops.

Fixing what you find

Almost every soil problem improves with the same answer: organic matter. Compost buffers pH, feeds soil life, improves drainage in clay and water retention in sand. I build my own house blend — a base layer of quality potting mix, compost, Texas topsoil, and natural additives — and for my more expensive plants I'll start with a FoxFarm base and build up from there. You don't need to buy your way to good soil; you need to feed it consistently for a few seasons.

Don't feed the plant. Feed the soil, and let the soil feed the plant.

Written by Jordan Polasek, founder of Texas Roots, from his greenhouse in El Campo, Texas. Free to share. If this helped, the best thanks is to grow something or pass it along.