Mowing Height Matters
Propoer mowing height is probably the most important parameter of proper lawn care, like other plants, organic lawns must manufacture sugars through photosynthesis in the leaves if they are collectively to develop into a high quality lawn. Turfgrasses mowed at low heights have limited leaf area to sustain photosynthesis rates necessary to maintain good plant vigor.
In addition to leaf area, a direct relationship exists between the height of the turfgrass and the depth and total mass of the root system. Research with Kentucky bluegrass has shown that root growth was more than twice as great when the grass was mowed at a 2.0 inch height verses a 0.75 inch height. In general, a lawn mowed too short will have a shallow root system with little total root mass. The impact of shallow, weak root systems is most apparent during summer stress periods. When soil moisture becomes limiting, the closely mowed lawns usually exhibit stress first and the loss of turfgrass plants is more likely. Higher mowing heights during the summer period will keep soil temperatures cooler, preserve soil moisture and help maintain turfgrass quality. Recommended mowing heights of cool season turfgrasses cultured in Ohio include:
Proper Mowing Heights During
Turfgrass Species Spring and Fall Summer Stress Periods
Kentucky bluegrass 2.0 – 2.5 2.5 – 3.0
Perennial ryegrass 2.0 – 2.5 2.5 – 3.0
Fine Fescues 2.0 – 2.5 2.5 – 3.0
Tall Fescue 2.5 – 3.0 2.5 – 3.0
Turfgrass mowed at the recommended height will have deeper, stronger root systems.
Mowing height can play an important role in prevention of lawn weed establishment. Research has shown that higher mowing heights result in fewer weeds per unit area. This is due to higher grass providing more shading and competition to the weed seedlings during the initial establishment phases.
The lawn should be mowed frequently enough so that no more than 1/3 of the leaf blade length is removed during any one mowing. For example, if Kentucky bluegrass is normally mowed at 2 inches, the height should not be allowed to grow beyond 3 inches before it is mowed back to 2 inches. If 1 inch is mowed, 1/3 of the total blade length is removed and the 1/3 mowing rule has been followed. During periods of active turfgrass growth, many lawns will require mowing more than once per week if this recommendation is to be followed. Proper mowing frequency is a key to successful implementation of the “Don’t Bag It” clipping return program. If extended wet periods prevent timely mowing and the turfgrass gets excessively tall, move the mower height adjustment to the highest setting and mow the lawn. Once the clippings dry, lower the height adjustment to the desired height and then mow the lawn a second time in a different direction. This approach is termed “Double Cutting.”
Additional Mowing Considerations
The direction of mowing should be altered every one to two mowings. Mowing at right angles (90 degrees) to the previous direction will help prevent the grass from repeatedly being pushed in one direction and laying over, an important consideration at high mowing heights. Also if scalping areas of the lawn is a problem, the different mowing directions will help minimize continual scalping in any one area.
All mowing equipment should be kept in good working condition. Having the mower serviced prior to the heavy spring mowing period will help ensure routine, maintenance-free mowing. Mower blades should be sharpened each spring and as needed during the season. A dull mower blade frays the ends of blades and results in brown tips which are unsightly and indicate damaged turfgrass.
Mow When Dry
Turfgrass should be mowed when it is dry. Wet grass is more difficult to cut and has the tendency to clog under rotary mowers. Mowing should not, however, be delayed for long periods of time because the grass is wet.
Fall Mowing Practices
During the Fall period, mowing should continue as long as the turfgrass is actively growing. If the maintenance height is 2.5 inches during the fall period, it is permissible to lower the height to 2.0 inches during the last 1 to 2 mowings of the year. A lower mowing height going into the Winter is important if the lawn is in a region susceptible to outbreaks of winter diseases.
Turfgrass clippings contain measurable amounts of nitrogen, phosphorus and potassium. Research has shown that when clippings are removed, 20 to 25 percent more fertilizer was necessary to maintain comparable color and quality as areas where clippings were returned. Contrary to popular belief, turfgrass clippings do not contribute to thatch accumulation if proper mowing practices are followed.