Don’t Salt the Soil!—Part 2

landscape of salt-resistant plants
A landscape of salt-resistant plants, including junipers, bearberry, Colorado blue spruce, aspen, and Japanese barberry

Last month I described a number of ways that salt can creep into our garden soil. Here are a couple more, plus what you can do about it.

Irrigation.
It may be a surprise to realize that simply watering your garden can introduce salts to your soil. That’s because water, even rainwater, contains some amount of dissolved salts. When we water, some of that water evaporates from the soil, but the salts are left behind. Those salts eventually build up; how long it takes depends on the salt content of your irrigation water, how often you have to water, and the amount of natural rainfall you get.

Typically, this is more of a concern for commercial growers in arid regions. In places such as California’s Imperial Valley, irrigation may have caused the desert to bloom, but it also created a significant issue with the salts left behind.

The accumulation of salts by evaporation can be slowed by applying several inches of mulch (yet another reason to mulch!). This reduces the amount of evaporation and reduces the need to add more water.

If you live in an area with very hard water, you may have a water softener. Because the resin beads inside are regularly flushed with a brine solution, small amounts of sodium end up in the softened water. How much depends on how hard your water is to begin with, but on average, eight ounces of softened water contains about the same amount of sodium as a slice of bread (20 to 25 mg). For most of us, this is not a health risk, but if you’re concerned about salts accumulating in your soil, simply make sure any outdoor faucets used for irrigation are connected to the water supply ahead of the softener, and consider using unsoftened water on indoor plants.

Now what?
The only way to know how much salt is in your soil is to have it tested. But then, what do you do if the test indicates a problem? There are several approaches for the home gardener.

First of all, try to eliminate the source of your salt. Avoid feedlot-sourced steer manure, don’t over-fertilize, use mulches, etc. It’s much better to avoid creating a problem in the first place!

If salt levels aren’t too high, try adding some (non-salty!) organic material, such as homemade compost. The organic particles bond with the salt ions, sequestering them.

You can try leaching the excess salts by flooding the area with a lot of water. The water will carry the dissolved salts below the root zone, or away through run-off. Be sure to determine where that salty water will go; you don’t want to transfer your problem to your neighbor’s yard! And be prepared for a shocker of a water bill!

The amount of water you’ll need depends on several factors, most importantly how saline your soil is. For details, consult “Solutions to Soil Problems: High Salinity” on the Cooperative Extension website.

Many plants can tolerate a higher salt concentration. Here are some suggestions that should do well in Colorado gardens:

  • Vegetables: It’s easier to list the vegetables that are particularly sensitive to high salinity: beans, carrots, lettuce, onions, bell peppers, sweet potatoes. Potatoes and broccoli have a small degree of tolerance; cauliflower and spinach much more so.
  • Trees: Amur maple, Austrian pine, black locust, catalpa, Colorado blue spruce, green ash, hackberry, honeylocust, Kentucky coffeetree, and various oaks. (Cottonwoods and aspen are also salt tolerant, but I can’t recommend them for city lots.)
  • Shrubs: Rugosa roses, alpine currant, bearberry, bridalwreath spirea, buffaloberry, burning bush, honeysuckle, juniper, coralberry, firethorn (Pyracantha), flowering quince, forsythia, lilac, ninebark,  shrubby cinquefoil (aka Potentilla), Siberian peashrub, snowberry,  sumac.
  • There were too many perennials to list here, good news for those of us who love growing flowers!

High salt levels are hard to overcome, but if you keep these insidious salt sources in mind, hopefully you’ll never reach that point. If you do find yourself overwhelmed, the best solution may involve building raised beds or removing the contaminated soil and replacing it with purchased top soil.

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