Walker: When moving to that new home, be sure the soil is up to par

U of I Master GardenerJuly 18, 2013 


The housing slump appears to be over. Houses are selling fast and new houses are popping up all over.

I recently had the opportunity to work with the owner of a newly built home. The builder installed lawn and a few shrubs in the front yard, but the backyard was a blank slate of rocky topsoil that had been brought in from an unknown source.

The first order of the day was to get the soil tested. The test came back showing that the soil is deficient in the three basic nutrients: nitrogen (N), phosphorus (P), and potassium (K). Of the minor nutrients, magnesium (Mg), copper (CU), manganese (Mn), iron (Fe) and boron (B) were in the adequate range. But zinc (Zn) is too low, sodium (Na) is three times higher than the norm and calcium (Ca) is four times higher than the norm! The pH of the soil is 7.9, which is at the high end of the normal range.

I did a little research to find out why the sodium and calcium are so high.

Soils in Southwest Idaho are full of caliche, a form of calcium carbonate that has hardened and formed a hardpan layer just under the topsoil. This hard layer restricts water flow which causes normal salts to build up. When the soil is dug up and moved, the salts and broken bits of caliche move with it.

Fortunately, the salt concentration is not high enough to be lethal to plants. The high calcium will interfere with the uptake of iron and zinc, but not to the extent that it'll be detrimental to plants.

It will take time to amend the soil with organic compost to make the soil ideal. In three to five years, the new home owner will have great soil for growing a vegetable garden and everything else from ground covers to trees.

In the short term, the lab recommended soil amendments in pounds per 1,000 square feet. This particular homeowner needs to add about three pounds of a general NPK fertilizer per 1,000 square feet. Elemental sulfur can be added to bring down the pH a little bit.

And the final recommendation to this new homeowner is to ask for compost as a housewarming gift.

If you have particular questions about gardening you'd like to see addressed in this column, send them to highprairielandscapedesign@yahoo.com.

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