One of the keys to successfully growing plants in yards and gardens is having good soil conditions, including physical (drainage) and chemical (fertility) components. Quiz yourself this week on some essentials of soil management. The answers can be found at the end of the column — no peeking!
Question 1: When gardening in heavy clay soil, what is the best material to incorporate to improve conditions for growing garden plants? Your choices are sand, limestone, compost, or gypsum.
Question 2: When planting trees or shrubs in soil with significant amounts of clay, what is the best way to manage backfill before putting back into the planting hole? Pick from heavily amend with organic matter, moderately amend with sand, do not amend the backfill, or put a layer of gravel in the bottom of the hole before backfilling.
Question 3: Which soil organism plays the biggest role in decomposing organic materials and making nutrients like nitrogen available to plants? Your choices include earthworms, fungi, bacteria, or nematodes.
Question 4: If a soil test shows your soil has a pH of 7.9, what is the best way to lower it to make it more favorable for plant growth? Choose from either limestone, potassium, sulfur, or muriate of potash.
Question 5: Which soil nutrient is associated with green color and vegetative growth in plants? Pick from either nitrogen, phosphorus, potassium, or calcium.
Questions one and two both deal with clay soils, which have exceedingly small pore spaces, causing water to drain extremely slowly. Compost is the best answer for question one, as adding organic materials such as compost help build soil aggregates and make pore spaces larger, thus improving drainage. When planting in clay soil (Question 2), it is best to return the same soil that was removed when digging the hole. Significantly amending it or adding gravel to the bottom will make drainage issues worse, leading to waterlogged roots.
Bacteria play the biggest role in decomposing organic matter (Question 3) and making certain nutrients, in particular nitrogen, available for plants. Beneficial aerobic bacteria prefer soils with a good mix of oxygen and water, as do plants.
Soil pH values above 7 (Question 4) are said to be alkaline and can be lowered by adding sulfur. Limestone can be used to raise pH on acidic soils (pH below 7). Do not add either without soil test results confirming an exact pH. Most plants prefer a pH that is slightly acidic, usually around 6.5.
Finally, nitrogen (Question 5) is associated with green color and vegetative growth in plants. Phosphorus is linked to root growth and flowering, while potassium helps with stress tolerances.
By Bruce Spangenberg, UW-Madison Division of Extension
