Organic matter always seems to be the soils cure all, magic elixir. Poor drainage? Add organic matter! Poor water retention? Add organic matter! Looking for a gentle fertilizer? Organic matter! First let’s clarify what organic matter actually is: Organic matter is decomposed plant or animal residue in a stage of decay. Common sources are compost, manure, leaf litter, and grass clippings.
Is it possible to have too much organic matter? The short answer is yes, over the past few years I have noticed that more and more soil tests show an excess of organic matter; most of the time this is considered overly rich soil. While there is no magic recipe to help balance your soil, a soil test can help reveal what the soil contains and where it is lacking. Ideally garden soil is 3-5% organic matter with an upper limit of 10%. More recently I have seen upwards of 13-20% organic matter. Excess organic matter can lead to high concentrations of nutrients such as ammonium, calcium, magnesium, potassium, and sodium. This can increase soil pH and make nutrients less available in soils. As a result, your plants may exhibit nutrient deficiency symptoms, despite an excess of nutrients in the soil. Plant symptoms can include leaf yellowing, burning, and stunted growth. You can also use physical soil signs as a cue, soils that are muck like and holding too much water, or not holding any aggregates (soil particles sticking together) and lacking structure for plant roots. In urban gardens, it can be very easy to build up an excess amount of organic matter (OM), because the soil space is very limited. If you are putting on 5 inches of leaf mulch annually, the plants are not always using the equivalent every single year. In addition, many people are being encouraged to fill raised beds with pure compost instead of garden soil or potting media.
What to do if your soil organic matter levels are too high:
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- Stop adding compost or other forms of organic matter.
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Allow the soil to breathe, do not cover with a layer of plastic mulch. This allows acidifying rain water and snow to infiltrate the soil. It also allows for better air exchange, speeding up the breakdown of the excessive organic matter.
- If needed, applying additional nitrogen can speed up the decomposition of the organic matter.
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Managing Fallen Leaves
With cooler autumn weather comes falling leaves. If leaves are not managed properly, they can damage turf grass underneath leading to sparse or dead grass next spring. The thick leaves smother out grass by limiting oxygen and staying too wet promoting fungal diseases.
Fully removing the leaves can be done through raking, blowing or using a collection bag on a lawn mower. Leaves can then be composted, burned, applied to planting beds for mulch, or removed by your local municipality.
Another option is to mow or chop leaves onto the lawn. This can help return organic matter to the soil, reducing the need for commercial fertilizers. When mowing, make sure the pieces of leaves are small enough to fall down into the grass. You may have to mow over the area several times, and you will likely need to mow several times throughout the fall. This is best done when leaves are dry.
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Something eating your plant? Need help identifying a tree? Interested in the best way to care for your lawn? Submit your questions online!
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| Kaitlin Bricco, Horticulture Educator |
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