Sul-Po-Mag-- better than Epsom Salts

By Richard Shiell

Magnesium is the reason plants are green. The chlorophyll molecule has at its center an atom of magnesium. The hemoglobin molecule that gives blood its red color is identical to chlorophyll except that at its center is an atom of iron.

Plants need only small amounts of magnesium, so it is classed as a micronutrient. Rosarians have found that supplementing with magnesium can encourage basal breaks (new canes from the base of the plant) and more lush growth overall. Note that soils in our area may be low in magnesium (mine was when I first had the soil tested by a lab). Other parts of the country have high magnesium levels so gardeners there shouldnít be adding more.

Magnesium sulfate is another name for Epsom Salts. Here we find an oddity of language; technically a salt is any crystalline material produced in an acid-base reaction. Salts include thousands of materials besides ordinary table salt, sodium chloride. In other words, there is no "salt" in Epsom Salts.

Sul-Po-Mag is short for sulfur potash of magnesia. It results from the combination of magnesium sulfate and potassium sulfate. The fertilizer formula is 0-0-22.

In my garden the native soil is quite alkaline. This owes almost entirely to a great abundance of sodium. In fact, "sodic clay" soils are very common in our region (ever been to Soda Lake?). Adding potassium is one of the best ways to achieve a balance of electrolytes in such soils. Gypsum may be added to supplement the calcium levels.

Many members of our rose society have seen one or two of my roses at meetings. I ascribe much of my success in this garden to building up the potassium levels in the soil enough to somewhat balance the sodium. Iím now on my third bag of fifty pounds of K-Mag (a brand name for Sul-Po-Mag).

If youíve not had your soil tested Iíd recommend contacting the local county extension agent and getting a list of labs that offer the service. Testing costs about seventy dollars. My garden soil is about due for another test (itís been a few years).

K-Mag is available from Britz Fertilizer (see previous article). Call ahead to see if its in stock, or they may have to get it from their main location in Fresno.