How Soil Tests Can Help with Tree Selection
Have you ever gone to a tree nursery and to your glee found what you thought to be the PERFECT tree for your home? Maybe you first saw it in a magazine, on TV or the Internet or you caught it on sale at Walmart. Wherever you saw it, you respond out of impulse and purchase it for your property. In no time, you have it in the ground and your taking selfies with it to brag to all of your friends on social media!
After a few weeks, months or years go by, you begin to notice it’s not looking as nice as it did when you planted it. “What happened? Why is it looking so sickly?” you wonder. Well… it could be any number of reasons:
- Transplant shock
- Poor root establishment because when it was planted it was not checked for encircling or girdling roots, etc.
- Planted too deep because instead of removing the excess soil around the trunk to locate root flare and main order roots, the planting depth instead followed the soil line already surrounding the trunk
- Not enough water from prolonged periods of drought and no irrigation system or too much water because it was planted in a low-grade area prone to flooding or pooling or it’s receiving too much irrigation
- Wrong tree species for the Hardiness Zone it was planted
- A variety with low resistance to insects, bugs, mites or diseases or was not poor quality tree stock
- Repetitive mechanical injuries from mowers, weed-trimmers, new construction, trenching, tree house, etc., including child’s play (climbing, swing, etc.) or animal induced injuries
- Incompatible or poor soil conditions (e.g. high alkalinity (pH) or high acidity, compacted, etc.)
Speaking of incompatible and poor soils… One of the biggest challenges in establishing some trees in Indiana clay soils is the high alkalinity. During the planning phase of tree selection, the step that is often overlooked is getting a soil test first. Becoming familiar with the following soil chart will aid you in your understanding of how soils can impact the success or failure of your tree(s).
After a laboratory analysis, a soil test report will typically show specific soil nutrient content, soluble salts, and the pH level, but the soil will not usually be tested for contaminants, such as bacteria, mold, fungi, herbicides, etc.
If contaminants are a concern (say, for example, bacterial problems associated with Crown Gall disease, which affects roses, euonymus plants, willows, etc.), then more advanced analysis is needed and that would require the help of a microbial services laboratory, which may charge a significantly higher fee.
Some items to look for in a soil analysis report: [You can click the example image below to open a new web browser tab for a larger view.]
- If certain plants are lacking color and looking yellowish rather than green, they may be suffering from Chlorosis. The pH rating may be an important factor. What is the soil pH rating? Is it too low, too high, or just about right? In a rating scale from 0 to 14, the optimal pH range for most plants is between 5.5 or 6.0 to 7.0. (7.0 is considered neutral.) In the example report below, the pH level of the soil sample analyzed is 7.3 (circled in red) which is considered high.
- The soil texture or percent sand, silt, or clay determines how much sulfur is needed to lower the pH. Low or insufficient Sulfur (S) may be insufficient to reduce the alkaline effects of the soil. In general, some nutrients cannot be efficiently absorbed by tree roots if the soil pH is too high. In the soil sample below the Sulfur reading (parts per million; see blue arrow) is 14 ppm. This indicates that Sulfur is high, but since the pH is still high also, this could indicate a problem related to soil texture.
- Should you add more Iron (Fe) into the soil for your Pin Oak or River Birch or White Pine, etc. to help their foliage green up better? Well, if the soil in this sample report above came from the property with those trees, we can see that the soil already has a “very high” concentration of Iron (see green arrow) at 154 ppm and thus, additional Iron is likely unnecessary.
- The same may apply if we were trying to resolve a lack of Manganese (Mn) in a maple tree to help restore color to the foliage. According to the analysis chart above, Manganese is 72 ppm, which is considered “very high”. (See orange arrow)
KNOWING your soil can also help you to understand why existing trees may be failing in health and a soil analysis may help guide you into smarter ways of addressing nutrient deficiencies and to stop wasting time on deep root feedings that your plants don’t really benefit from because of improper soil pH levels.
Alkaline (High Soil pH) Tolerant Trees
Native (Indiana) Species (Non-invasive)
- Black Maple (Acer nigrum) but beware of Asian Longhorn Beetle!
- Northern Catalpa (Catalpa speciosa)
- Common Hackberry (Celtis occidentalis) but beware of Asian Longhorn Beetle!
- Eastern Redbud (Cercis canadensis)
- Yellowwood (Cladrastis kentukea)
- Cockspur Hawthorn (Crataegus crusgalli)
- Downy Hawthorn (Crataegus mollis)
- Green Ash (Fraxinus pennsylvanica) but beware of Emerald Ash Borer and Asian Longhorn Beetle!
- Kentucky Coffeetree (Gymnocladus dioicus)
- Honeylocust (Gleditsia triacanthos)
- Eastern Red Cedar (Juniperus virginiana)
- Crabapple (Malus spp.)
- American Hophornbeam (Ironwood) (Ostrya virginiana)
- Bur Oak (Quercus macrocarpa)
- Chinkapin Oak (Quercus muelenberghii)
- Black Locust (Robinia pseudoacacia) though sometimes invasive
- American Linden (Tilia americana)
- Elms (Ulmus spp.) Purchase only Dutch elm disease (DED) resistant hybrids (such as, ‘Triumph’, ‘Accolade’, and ‘Commendation’) or DED tolerant American Elms, but beware of Asian Longhorn Beetle!
Non-native Species (Non-invasive)
- Ruby Red Horsechestnut (Aesculus carnea) but beware of Asian Longhorn Beetle!
- Katsura Tree (Cercidiphyllum japonicum) but beware of Asian Longhorn Beetle!
- Hardy Rubber Tree (Eucommia ulmoides)
- Ginkgo (Ginkgo biloba)
- Black Spruce (Picea mariana)
- Silver Linden (Tilia tomentosa)
Trees to AVOID
- Firs (Abies spp.)
- Red maple (Acer rubrum) but beware of Asian Longhorn Beetle!
- River birch (Betula nigra) but beware of Asian Longhorn Beetle!
- Dogwood (Cornus spp.)
- American Sweetgum (Liquidambar styraciflua)
- Spruces (Picea spp.)
- Pines (Pinus spp.)
- Pin oak (Quercus palustris)
- Bald Cypress (Taxodium distichum)
- Hemlock (Tsuga)
“HOW- TO” VIDEOS
Lindsey Purcell (Purdue Extension Urban Forestry Specialist) offers expert advice on how to select your tree here:
“Planting Your Tree Part 1: Choosing Your Tree – FNR-538-WV”
Once you’ve selected your tree, plant it right! Lindsey Purcell shows you how: “Tree Planting Part 2: Planting a Tree, FNR-540-WV”