Beat Weeds with Grass Seed
Sean Breckin, AOLCP
Aerating Versus Seed Slicing This Spring


In an all-natural Organic Turf Care (OTC) program, the best way to beat weeds is with grass seed. Soil temperature, germination time frames, and pH all affect growing healthy grass. In the Northeast, the window to overseed caps by the end of May.

Whether dealing with residential or athletic fields, the goal is to get coverage as quickly as possible in the spring: quick coverage helps suppress weeds and the spring overseeding window to establish grass can be very short, so choosing the right grass seed blend is important.

Pro’s and Con’s of Grass Seed Cultivars

Cool-season grasses do best in the Northeast. Shoots begin developing in the temperature range of 60°to 75°F. Roots develop at temperatures of 50°to 65°F. There is no one best cool – season grass variety. A blend of turf grass varieties will do best based on site conditions.

  •  TriRye Perennial Ryegrass:—known for quick germination (5-7 days), good wear tolerance, average nutritional needs, fair heat tolerance but poor shade and drought tolerance.  Goes dormant in summer heat and drought.
  • Turf Type Tall Fescue:  average germination (10-14 days), very good drought tolerance, good wear, shade, and heat tolerance. Turf type tall requires less nutritional needs but does not compete well in established turf so use a blend with high % TTTF and lower perennial rye or Kentucky blue. Can do dormant in the summer but its outstanding heat tolerance keeps a tall canopy in irrigated lawns keeps performance going all summer – the prime time to compete against undesired weed species.
  • Fine Fescue: average germination (10-14 days), excellent in shade, low nutritional needs, very good in drought, fair heat tolerance but low wear tolerance.  Not for sunny areas.
  • Kentucky Bluegrass: slow germination (21-28 days), good wear tolerance, highest nutritional needs, fair in heat, poor shade and drought tolerance.  Can be difficult to establish in spring. Kentucky blue performs best in early summer and fall – it will avoid dormancy is well irrigated lawns over the summer.
PJC’s top spring seed performers…

Athletic Fields:  100% Tri Rye in April-May 15th followed by 80% Perennial Ryegrass, 20% Kentucky Bluegrass in May or 70/20/10 by June 15th.

Residential Lawns:  100% Tri Rye for sun and 85% Fine Fescue, 10% Perennial Ryegrass, 5% Kentucky Bluegrass for shade.  If unable to water skip spring seeding and focus n fall

Once you’ve chosen your seed, how you get the seed to soil contact is as important.  For small thin and damaged areas, mixing the seed with a loam/compost mix, broadcasting over affected area and raking it out is sufficient.  On larger areas aerate and broadcasting seed or seed slice.

Pros and cons of Aeration and Overseed versus Seed Slicing.


Pros— A core aerator pulls plugs of soil and deposits them above ground. This opens up space for air, grass seed and water to enter the soil, and for turf-grass roots to spread. Additionally, core aeration is our best mechanical measure to alleviate highly compacted areas. Athletic fields are highly susceptible to compaction and most weeds that thrive on athletic fields are a result of compaction, which can bind calcium or limit pore space for grass roots to thrive. Spring aerations with fast germinating rye grass present your best opportunity to establish new turf grass in short windows like spring break and give you more turf coverage going into the heat of summer.

Cons—However, as cores are brought to the surface, there’s risk that weed seeds are also brought to the surface and given a chance to germinate. These weed seeds would have otherwise remained buried and the existing turf cover would have kept them at bay. Due to this potential risk, core aeration should be avoided on residential lawns in the spring unless the area is so compacted that water can’t filtrate the soil profile. Aeration and overseeding is highly labor intensive, and while the soil and turf benefits are outstanding – it can be difficult for landscapers or athletic field managers to keep on top of other practices like mowing and irrigation repairs, so be sure to schedule your time well and don’t miss the opportunities to best improve your playing surfaces. 


Pros—A slice seeder (also known as a slit seeder) is a great alternative to core aeration for spring overseeding. These machines cut small slits into the soil, and then deposit grass seed into the cut rows. They provide great seed-to-soil contact to help with germination, minimize soil disruption, and reduce the risk of exposing weed seeds in your lawns. Slice seeding is an excellent way to get bare areas to take seed as you can ‘slice’ into the soil in multiple directions. Additionally, slice seeding is an incredible way to establish new lawns alternatively to using sod which is costly and labor intensive and results in a ‘sod layer’ that can inhibit good root formation through the soil profile.

Cons—It’s important to note that seed slicing does not address compaction, and lawns should still be aerated and overseeded in the fall. Further, slice seeding is not an ideal approach to overseeding very well established turf areas – it is designed to help establish new lawns or turf stands and if you already have a well performing turf area – slice seeding may not have the desired effect of introducing new turf species as the lawn or field is already highly competitive with well-established turf.

Remember: the goal is to promote quick coverage to help suppress weeds and now’s the time to do it!

Note:  Since it can take up to 18 months for grass to become fully established from seed, anticipate some die off from spring over-seeding as you enter the heat of the summer.  Plan to follow up with a second overseed in the fall. If budget only allows for one over-seed a season, wait until fall. Fall is the best window to focus on establishing grass from seed to thicken the lawn.