Every so often someone who may not agree with me asks a question. One of these is why I don’t recommend aluminum sulfate to acidify my soil and lower the pH. I lower the pH of my soil as I have a number of plants that do not do well in our alkaline soil. Included are azalea, rhododendron, holly, and blueberries. Many years ago, in my first agronomy class, we were told that too much aluminum would tie up the phosphorus, making it impossible for the plants to get any. Phosphorus is one of the three major components you will see listed on any bag of fertilizer. The first number is for nitrogen (N), the second number is phosphorus (P), and the third number is potash or potassium (K).

          The first sign of a phosphorus deficiency is a reddish, purple discoloration of the leaves of a plant.  Phosphorus is essential in a number of plant functions such as flowering and fruiting, and seed production, resistance to disease and root development. The starter fertilizers that you see every spring planting time are high in phosphorus as well as the ones who promise to make your plants bloom. So you can see it would be easy to overdose with aluminum, and it is rather expensive compared to granular or powdered sulfur. 

          Another question that is often asked is about Epsom salts and why or where it should be used. The book “Clematis Care Manual” by Mary Toomey, says that magnesium deficiency causes clematis leaves to turn yellow between the veins. Also it causes leaves to drop. She recommends the use of Epsom salts at the rate of 1 oz per 10 square feet of soil. It should be scratched into the soil during autumn. In the American Rose, Belindy recommends one tablespoon of Magnesium sulfate (Epsom salts) around each rose bush once a month during summer and a handful early in the spring, sprinkled dry and then raked and watered in to promote new canes and handsome leaves. You can buy it in a drug store or in 50 pound bags at a farm supply store.  Many tomato growers treat their plants in this same way. George mentioned magnesium in one of his earlier articles.

          Trace element fertilizers are also called micro-nutrients. I am asked, “What are they and what do they do?” In general if you are making and using compost you already have them as what comes from a plant feeds another one.  The definition is “those chemicals used in very small quantities by plants but essential for their well being”.

          According to Elizabeth Still in “Secrets to Great Soil”, micronutrients deficiencies occur only in very acid or very alkaline soils or intensively gardened ones using only “synthetic” fertilizers without compost or other organic material.  Among these micronutrients are boron, copper, manganese, molybdenum, and zinc. It is better to check before you add any of these as plants use very little and an overdose can be very toxic. She also recommends adding them to the compost pile rather than a direct use.            Sometimes if you read the “doom and gloom” magazines there are statistics about how little nutrients we are getting in our food as the soil has been “used up” with the plants unable to pick up these things because they aren’t there. My favorite plant food for many years was wood chips used for horse bedding and then shoveled outside in huge mountains to sit in the sun and rain where it partially composted. Dug in every fall it supplied all the nutrients I needed as well as constructing spaces for air and water.  The fall application gave it time to break down partially thus releasing the nutrients.

          Another questions asked is “How often and how deep should I till?” I can no longer till as my plants are too close together with no free space, unless something terrible happens that really disturbs the garden. One agronomy professor I had hated rototillers as they:

1.     Changed the soil from good structure to dust that would blow away, and

2.     Brought up all the buried weed seeds to the surface where they could germinate.

My compost, which never gets really finished, is on top of the soil for earthworms to eat and take down to the roots. As it goes through their digestive system it becomes “castings” which you can buy to add to your soil.  Have you looked into the new “No Till” concept that farmers are using and how it works? It keeps soil from erosion during winter and fall rains, as the roots decay they leave passage ways for water and fertilizer to run down.

          Another question I was asked is “Have you ever dug in your garden and met hardpan”? “Hardpan” is a hard layer of soil that does not let water, roots, or anything else get any deeper. You can make “hardpan” in your own garden by digging or tilling to the same depth every time or by walking or using equipment on wet clay soils. This is especially a problem with tillers when you continually till at the same depth. Those tines pound the ground at the same depth year after year and create hardpan.

          When my husband and I tried to plant trees in the parkway, they didn’t do well and by digging I discovered hardpan just below the root ball. As a result, the root ball space was holding water, so of course they were drowning.  We went on either side of their root ball and dug holes down until we reached a looser layer of soil and then filled the holes with rock and gravel to produce drains for each tree.  During construction that area was used for parking and was heavily traveled by equipment thus making a different species of cement and a layer of hardpan. Now, because of our double digging and the addition of compost, that area is some of my best soil.  I can actually plant with a spoon. The bad part is that it erodes easily and I can’t use that soil to plant water lilies as the soil would float away when the container is placed into the pond. You can help your garden soil by double digging, adding lots of organic matter such as compost, and not walking on the soil when it is wet. Plants will grow much better if the soil is not just the hard clay. The ideal is about 30% compost to 70% soil.