There is a persistent rumour going around that cutting your lawn extremely short before the winter is beneficial, or even necessary to avoid growing mould under the snow. (I also think that many people think somehow that cutting extra short will somehow turn your lawn mower into a leaf-sucking vacuum cleaner??)
This seems to arise from a misunderstanding about the plant health problems lawn debris can cause if left over the winter. Some people seem to think that leaving ‘long’ grass leaf blades on your lawn will invite the same mould problems a carpet of tree leaves would.
But the lawn mowing mantra we repeat all summer – two and a half to three inches for best grass health – is true even in the fall. There is never a valid time to mow down bluegrass, ryegrass or fescues shorter than their ideal healthy height.
Stop shaving your grass down in the fall.
Perennial plants store food for the winter as temperatures drop in fall, and your grass is no exception. Grass stores carbohydrates in its roots and crown – the part of the grass plant right above the soil that the leaf blades grow from. Cutting too short shocks the grass, makes it harder for the plant to absorb the sun’s rays, and can easily damage the crown of the grass plant.
Cut the blade too short and your grass may go hungry over the winter and will likely spend the spring recovering from shock.
Mould grows on damp organic matter with poor air flow. If the debris – such as leaves – is in small enough pieces air can flow properly and it will break down quickly. Mould doesn’t have a chance to get started!
Three studies by Michigan State University showed that if leaves are mulched to dime-sized pieces 100 pounds of leaves (in an area as small as 1000 square feet) will break down easily . You don’t even need special equipment, a few passes of a sharpened blade on a mulching lawn mower will do the job. That means less raking and bagging, and fewer trucks hauling leaves to community compost or worse, landfill. Plus your lawn gets all those nutrients back! Just make sure you are having your lawn fertilized with a proper blend of nitrogen fertilizer to help complete the decompostion process.
Shredded leaves and fallen conifer needles also make good mulch under trees, helping to prevent moisture loss and returning nutrients to the roots. Rake or blow the needles or mulched leaves under a stand of trees and they will also benefit.