Rejuvenating an Existing Lawn
A lawn that is thin, injured or diseased may benefit from either renovation (starting completely anew) or partial renovation. A partial renovation of an existing lawn involves core aeration and overseeding to thicken thin turf or introduce better adapted turfgrass seed varieties. Shade-adapted bluegrass and fine fescue can be introduced into a lawn that is thinning from the shade cast as trees grow larger.
The use of hybrid bluegrass varieties (Kentucky x Texas) in full sun areas can be desirable for their heat tolerance, deep rooting and potential to require less irrigation. Hybrid variety names include 'Reveille', 'Thermal Blue', 'Dura Blue', 'Solar Green', 'Longhorn', 'Bandera' and 'Spitfire'.
September is a good time to overseed along the Front Range and Western Slope. Start by thoroughly core aerating the lawn, perhaps with two passes made at right angles to gain more holes than usual. To be successful, the seed must contact the soil and it must be kept moist for germination. Seed won't germinate if it rests on a mat of grass leaves. The seed that falls in the aeration holes will contact the soil for germination and be protected from drying sun and wind to stay moist.
The other necessary follow-up step is frequent, light irrigations to keep the seed moist during the 21 day bluegrass germination period. Water for only a minute or two several times daily depending on temperature. Do not overwater during the 3 week germination time. This wastes water and creates unfavorable soil conditions for the roots of existing grass and trees.
Plumes of the new grass should emerge from the germination holes and eventually spread due to their better adaptation for the environmental conditions (light, heat or moisture, etc.). This will take several years. There is no reason that overseeding can't be done next spring or fall if you want to speed the process. Obviously it is necessary to choose a grass species compatible to the existing lawn for this to be successful.
For information on grass compatibility and the renovation process, see the CSU Extension fact sheet 7.241 on Renovating the Home Lawn.
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Updated Friday, April 19, 2013