Gardening: Debunking common myths about soil
‘Fake news’ is not only found in the political realm. It has been a phenomenon in the gardening world for as long as I can remember.
One of the ‘fake news’ stories that has been circulating for years is that you can’t grow plants under a spruce or pine tree because the soil is “too acidic.” While the needles on the tree are acidic in nature, it would take an awful lot of needles to actually change the pH of the soil.
Perhaps this rumour started because evergreen trees grow naturally in northern Saskatchewan, where the soil is more acidic. But in central and southern areas of the prairies, the soil is basic (with a high pH) and changing the pH of that soil is very difficult.
The real reason plants don’t grow well under evergreen trees (especially shallowly rooted spruce) is that it’s usually quite shady, but mostly because it is very dry. Large trees use copious amounts of water to survive, and smaller plants trying to grow under an evergreen have a hard time competing for moisture, nutrients and light.
Among the ground covers adapted to dry shade are Canada violet (Viola canadensis), bergenia (Bergenia cordifolia) and false Solomon’s seal (Smilacina stella). They will need regular watering during their first season until established.
Another gardening misconception is that you can easily change the soil pH. Adding lime to a soil to increase the pH or adding sulphur to a soil to decrease the pH is not practical. The amount of lime or sulphur you would have to add to a soil to change its pH significantly would be enormous.
For example, a University of Wisconsin Horticulture website recommends that if your soil has a pH of about 7.4 (Saskatchewan soils are typically at this pH or higher), and you want to plant blueberries which require a soil pH of 5.5, you should apply approximately 3.5 to 5.5 kg (16 – 24 cups) of aluminum sulphate or two and three-quarters to four cups of elemental sulphur PER PLANT.
Planting into this amended soil should be delayed for about one month after application to avoid root burn. After planting, the soil must be amended on a regular basis to maintain this pH. Furthermore, when large amounts of sulphur or gypsum are added to the soil, the availability of other nutrients may be compromised. For example, gypsum (lime) can increase leaching of iron and manganese, leading to deficiencies of these nutrients.
It is far better to grow plants that are suited to your soil rather than trying to adjust your soil pH to plants that demand a significantly different pH.
Watering your tomatoes with milk to help prevent blossom end rot is another enduring myth. Perhaps it started with the dairy industry when milk sales were slow.
The theory that a lack of calcium generally leads to blossom end rot in tomatoes is correct. But it is usually not a lack of calcium in the soil, but rather a lack of regular calcium to the plant due to infrequent or irregular watering that is the cause.
There is usually ample calcium in a healthy soil for tomato fruit production. However, uneven watering (ie., letting the plant dry out and then overwatering) will disrupt a continual supply of the available calcium to the plant.
The best way to avoid blossom end rot in tomatoes is to provide adequate water to the tomato plant throughout the growing season. Mulching the base of the plants will help conserve and even out soil moisture. Save your milk for snack time with fresh chocolate chip cookies.
To learn more about our many gardening myths, some old and some new, visit the University of Saskatchewan’s Plant Science booth at Gardenscape, Prairieland Park, Saskatoon, March 23 to 25. Speakers provide informative gardening-related talks; local gardening organizations share knowledge; and the City of Saskatoon and the University of Saskatchewan provide current information on a variety of topics. See www. gardenscapeshow.ca for details.
This column is provided courtesy of the Saskatchewan Perennial Society (SPS; saskperennial@hotmail. com). Check our website (www. saskperennial.ca) or Facebook page (www.facebook.com/saskperennial) for upcoming public education sessions, garden tours and other events.