Mythbusters: Epsom Salt and Tomatoes

Jesse Fulbright, MSU Liberty County Extension

Memorial Day seems to be a traditional time to put out some of tender garden plants in our area, such as tomatoes.  There are always little traditions or ways of planting that are passed down in families or make their way into popular culture.  Some of these are steeped in research-based techniques, while others may be great in areas of the country but not necessarily here.  One method of planting tomatoes that I hadn’t heard until recently was about adding Epsom salts to the hole when planting your tomatoes.  Some people will say that adding Epsom salt prevents blossom end rot in tomatoes.  It’s time to play myth buster and debunk this method of gardening. 

According to a North Dakota State University Extension publication, adding Epsom salt leads to more blossom end rot.  Blossom end rot is caused by a deficiency of calcium, or something that might be more common in our area, infrequent watering.  Typically, we have enough calcium in our garden soils for tomatoes and peppers.  What can happen though is that we get busy during the summer and our watering habits fall by the wayside.  As plants are watered, and then not for periods of time and then watered again, calcium will be deposited only as far as the water gets and then it doesn’t get picked back up again. 

Photo courtesy of Michigan State University Extension

Now, back to the topic of Epsom salt.  Epsom salt contains magnesium sulfate, no calcium at all.  Adding Epsom salt to the soil may create more rot since magnesium and calcium compete for uptake into the plant.  The more magnesium in the soil, the less chance that calcium will be absorbed.

So, what can we do to prevent blossom end rot?  As I mentioned, typically we have enough calcium in the soil, so we don’t focus on the soil in this instance.  Instead, focus on watering.  The uptake of calcium depends on the uptake of water.  Irrigate regularly.  Avoid the extremes of waterlogged soil and droughty soil.  You might consider mulching around your plants to maintain consistent levels of moisture in the soil.

When weeding, consider cultivating shallowly.  Don’t damage the roots of your vines.  We need these roots to absorb calcium.  Also, avoid overfertilizing, especially with ammonium nitrogen fertilizers such as ammonium nitrate and most complete fertilizers such as 10–10–10.  Ammonium competes with calcium for uptake.  Calcium nitrate is a better choice.

Vines should be green but not lush.  Lush vines are more likely to suffer rot since actively growing leaves take calcium from the vine before the fruits get it.  As a general rule, don’t side dress a vine until after its first fruits set.

Calcium sprays might or might not help.  Mix 4 tablespoons of calcium nitrate per gallon of water.  Spray fruits, not leaves, two to three times a week.  The key time is when tomatoes are dime-sized or smaller.

Setting Tomatoes

Jesse Fulbright, MSU Liberty County Extension

In my visits with people in the community there is a growing unrest to get out in the gardens more and plant.  With this express purpose in mind, I wanted to talk this week about growing tomatoes, specifically, setting the plants.  This information comes from an Extension MontGuide about growing tomatoes that is available through your local county Extension office.

Set tomatoes in the garden after the danger of frost has passed.  Hopefully we are past this point, but please check your weather forecast before planting.  Plants of determinate cultivars and staked indeterminate cultivars need about four square feet/plant to develop normally.

Late afternoon of a calm, cloudy, humid day is the best time to set out transplants.  Set the plants an inch deeper than they grew in the container and tamp the soil firmly about the roots.  Water the plants well with a starter solution to eliminate air pockets about the roots, to settle the soil, and to provide water and nutrients for rapid growth.  If the transplants are spindly and have long stems, lay the stems about an inch below the soil line, letting only the upper several inches of the stem protrude above the surface.  This is called trench planting.  Tomato stems will produce roots along their entire length and this will help the plant develop a larger root system and larger, healthier plants.

Right after transplanting you can take steps to protect the nascent plants by covering them with things like row tunnels. These protect the plants from hot, drying winds, increase the humidity within the canopy to decrease wilting, and warm the plants during the early season when air temperatures are often cool.  All of this helps the plants grow faster.  Plastic milk jugs and old tires don’t substantially speed plant growth, though they can protect against wind damage.
Another way to speed plant growth in our short season is to use plastic film mulch.  Organic mulches are okay in summer but they keep the soil cool in spring and slow plant growth.  Red film mulches speed soil warming and thus root growth, help control weeds, speed tomato fruit ripening and conserve soil moisture.  Black mulches conserve soil moisture and control weeds.  If you decide to use plastic, prepare the soil as you normally would, then roll out the plastic and cover the edges with stones and soil.  Punch holes where you decide to plant and set the transplants through the holes.  Irrigation water will get to the plants through those same planting holes.  Be sure the soil is moist before you lay the plastic.

Lastly, you can cover the plants with floating row covers.  These lay on the plants and hold heat in the plant canopy to speed growth.  They tend to blow away where there’s wind, however, unless you anchor them.