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Landscape Notes: Fall Projects

By: Jon Morgenson, Assistant Horticulturist 

Now through the end of October is the best time for a few turf improvement projects.

Weed Control

If dandelions and other broadleaf weeds like white clover or creeping Charlie are invading your cool season turf areas, now is the best time of year to control them. These weeds are more noticeable when they are flowering earlier in the season but controlling them then versus now is less effective. Perennial weeds like dandelions are moving sugars produced through photosynthesis in the leaves down to the roots for winter storage at this time of year. Chemical weed controls applied at this time of year are also moved down into the roots resulting in a better “Kill”. Applying a fall weed control product will also control winter annuals (henbit and common chickweed) that germinate in the fall and biennial weeds like thistle.

Other benefits to controlling weeds at this time of year include less stress to turf areas with lower air temperature and protection of surrounding plantings like flower beds, trees and shrubs by lowering the risk of chemical volatilization which can occur during periods of high temperature. Liquid chemical applications applied by spraying can still damage plantings at this time of year through direct or indirect contact with desirable plants. Wind speed and direction should be observed during applications.

Spot treatment of weedy areas is preferred to wholesale treatment of large areas if at all possible. Identify the weeds you wish to control and select an herbicide labeled for use on those weeds. Amine and low volatile formulations of herbicides are available and should be selected. Also keep in mind that pollinators such as bees are still very active on some of our flowering weeds so use caution when applying chemicals.

Core Aeration

Core aeration can be done through the end of September. Cores or plugs of soil are removed from the turf and dropped on the turf surface to help improve air and water infiltration on heavy and compacted soils. The soil should be slightly moist but not wet when aerating. This turf improvement practice should be done every few years or every year on compacted soils.


Possibly, contrary to popular belief spring is not the best time to fertilize cool season turf (blue grass and tall fescue) areas. The largest portion of nitrogen fertilizer applied to turf should be applied in late summer and again in late fall. I understand that two applications of fertilizer would be a hassle, so make one application from now through about the time of your last mowing in October. By fertilizing now the turf gets a boost while it is still actively growing and it will help the turf overwinter in stronger condition.

Spring fertilization on the other hand causes too much early succulent growth increasing mowing frequency and it gives a boost to young competing weeds.

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