Is Utah Soil Alkaline?

Most Utah soil is alkaline, averaging around pH 8.0, because it’s packed with natural lime (calcium carbonate). You can try, but odds are you can’t change that very much. Fortunately, most vegetables grow happily in it, and the problems it causes have simple fixes.

Typical pH

Around 8.0 (neutral is 7.0)

Fine for

Most vegetables, which grow well between about pH 6 and 8

Main problem

Iron chlorosis: yellow leaves with green veins

Never add

Lime or wood ash

Test first

A lab test costs a few dollars; home kits give a fair estimate

Why Utah soil is alkaline

In dry climates, minerals that rain would wash away in wetter places just kind of stick around (similar to the dreaded Utah Inversion). Over thousands of years, Utah soils built up calcite, the same mineral as limestone, which typically makes up 15 to 40 percent of the soil by weight. Our irrigation water is alkaline too, so every summer of watering adds a little more.

Why you can’t just lower the pH

I’ve been there, pouring a bunch of acidic mulch into a bed trying to adjust the pH. Sadly, it’s an expensive and losing strategy (unless you’re importing a bunch of soil for a discrete, above-ground bed). The lime works like a giant buffer. Any acid you add, such as sulfur, simply dissolves some of the lime and gets used up, and the pH barely moves. To give a sense of scale, the top foot of a quarter-acre lot holds about 10,000 pounds of calcite for every 1 percent in the soil, and most Utah soil has 15 to 40 times that.

So the smart approach isn’t fighting the soil. It’s choosing plants that like it, and helping the ones that struggle.

What alkaline soil does to plants

At high pH, iron and a few other nutrients are in the soil but locked up where roots can’t reach them. Enter a condition called iron chlorosis. You can identify plants affected by iron chlorosis by noting leaves turn pale green or yellow while the veins stay green. In bad cases, leaves go nearly white, edges scorch, and branches die back.

Plants differ widely. Maples, pin oaks, willows, dogwoods, raspberries and strawberries are especially prone; two plants side by side can look completely different.

How to garden well with alkaline soil

1. Choose plants, and plant varieties, that tolerate it. This does more than any amendment. Ask a local nursery which varieties handle high pH.
2. Water deeply, then let the soil dry. Soggy soil makes chlorosis worse, especially in heavy clay. Soak the root zone, then wait until it dries before watering again.
3. Add compost every year, in moderation. Organic matter improves Utah’s typically low-organic soils, and may nudge the pH down a little.
4. Treat chlorotic plants with the right iron supplement. Yes, there are supplements for plants. You can use one called an iron chelate. The right iron chelate for chlorotic plants will be labeled with a daunting series of letters that look like this: Fe-EDDHA. This form keeps working above pH 7.5. Work the supplement lightly into the root zone, or water it in, each spring as growth starts. Most plants need it every year. For trees and shrubs, avoid the other type of iron supplement, plain iron sulfate. That one goes on the soil and rarely works here, except on lawns.
5. Grow acid lovers in containers. Blueberries and their kin need an acidic potting mix, such as one based on peat. Even then, alkaline tap water slowly pushes the pH back up, so remember your iron chelate on occasion!

Notes from My Garden

I’ll admit I was slow to embrace the limitation of my alkaline soil. There are so many plants that I simply adore, who don’t adore me back. Or, I should say, don’t adore my dirt.

My family has a rich British heritage, so naturally I’d look for azaleas, rhododendrons, and camellias to put in my garden. To make it worse, I have fond childhood memories of my mother’s gardenias.

But even worse around where I live are the tricky box stores selling red maple trees to unsuspecting gardeners. We have natural Maple tree color all over the Wasatch Front, but these Maples are more often than not of the Bigtooth variety, which can handle our iron situation significantly better. I have a good friend who is chained to a mature Maple tree that requires expensive iron supplementation each year. The tree is gorgeous. And for the maintenance cost, it better be.

Can I grow blueberries in Utah?

In the ground, blueberries struggle. In a large container or a lined raised bed filled with an acidic, peat-based mix, you get a much better shot. Plan on watching the pH, because our alkaline water nudges it upward every time you water.

Should I add sulfur?

Only if a soil test shows pH above 8.0, and with modest expectations. The usual rate is 6 to 10 pounds of elemental sulfur per 1,000 square feet a year, retesting as you go. In lime-rich soil, it may barely move the needle. But again, worth a shot if you go in with your eyes open.

What about gypsum?

Gypsum doesn’t lower pH or loosen ordinary clay. It’s only for sodic soil, which has too much sodium, and it’s only to be used when a lab test confirms it. Compost does more for clay than gypsum will.

Is “alkaline” the same as “alkali”?

This is a tricky trap. They’re not the same, though they’re practically spelled the same. Alkaline means a pH above 7. Alkali is a general term for salty soil. A soil can be one without the other, and plenty of Utah soil is alkaline without being salty.

Common mistakes

• Adding lime or wood ash. Both raise pH, and Utah soil is already high.
• Buying “alkali fighters.” Gypsum products don’t fix ordinary alkaline soil.
• Overwatering yellow plants. It often makes chlorosis worse, not better.
• Planting azaleas in the ground and hoping. I’ve been there. I feel your pain!

Related: What Is Zone 6b? · When to Plant Tomatoes in Utah