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My lawn has predominantly fine fescues, but before I knew the different kinds of turf grasses, I bought several big bags of Scotts northern seed mix, which turned out to be perennial ryegrass. Several online sources suggest mowing perennial ryegrass at 1.5 -- 2.5 inches and twice a week. I've only been able to mow once every five days and I'm mowing them at 3 -- 3.5 inches. What happens when we let the grass grow more than the suggested heights?

Not sure if and how these are related, but three observations: 1) the patches of perennial rye grow very fast between mowings. I often ended up cutting the top blades more than the recommended 1/3; 2) The grasses are very stemmy; 3) Either it's the hot spell in northeast US in late May or that too much blades have been repeatedly cut, some of the perennial rye patches are showing brown blades (and stems). Did I keep the grass too high or did I not mow often enough? What should I do going forward?

UPDATE Seed mix composition

Seed mix

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  • I'm in the UK so the climate is different, but with ryegrass you have two options: cut it short, or say goodbye to everything else in the lawn. FWIW, in the UK lawn mixtures usually contain ryegrass, but typical "non-professional" lawnmowers have a maximum cut height of 3 inches, and 1.5 inches is a more typical setting - or even 3/4 or 1 inch if you want a "top quality" lawn and are prepared to do the work to keep it that way. Anything cut higher than 3 inches is a "football [soccer] pitch", not a "lawn".
    – alephzero
    Commented Jun 17, 2021 at 11:19
  • @alephzero - standard lawn height in the US is now at least 3 inches, due in part to water conservation efforts in many parts of the country (my one-year-old electric mower has a max cut height of five inches). Higher-cut lawns have deeper roots, help shade out weed seeds from germinating, and help keep the lawn from drying out prematurely. In the northern US, the dominant grass type is Kentucky Bluegrass, which is rhizomatous (and a nasty garden weed, which is why we use plastic edging here). Many old guys still scalp their lawns, and they're the ones with the high water bills :)
    – Jurp
    Commented Jun 17, 2021 at 13:23

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According to The Lawn Institute (specifically, this page), cool season grasses should be mowed at anywhere from one to four inches. This includes perennial ryegrass. The growth rate you describe sounds more like annual ryegrass to me. This grass is often included in less-expensive grass seed mixes because it sprouts very quickly, providing 'instant green".

There are a few red flags with the Scott's mix you linked to:

  • They don't list the grasses included in the mix. Under US Federal law, there must be a tag sewn to the bag that shows the exact types of grass included in the mix, by percentage of seed in the mix.
  • The page says that the seeds will germinate in 5-10 days. Five days is too fast for perennial ryegrass and any of the fescues (they take at least seven days to germinate).
  • The mix says that it's for sun or shade, but probably doesn't contain much if any bluegrass because that germinates in a minimum of 21 days.
  • At $2 a pound, even at Walmart, the seed is too inexpensive to contain high-quality grasses.

If you haven't yet gone through a winter with your new lawn, then you may be looking at the annual, rather than perennial grass. Did the mix bag come with the mandatory tag? If so, what grasses did the mix contain?

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  • I added a tag listing the ingredients. The mix does have significant annual seeds but since we went through a winter in some areas with this mix, perennial rye should be what I'm dealing with. Also, they took 7 - 20+ days to germinate. So mowing at 3+ inches is not going to an issue for perennial rye? I was thinking it might encourage the grass to produce seed heads and thus more stemmy.
    – Roc W.
    Commented Jun 17, 2021 at 14:57
  • If that was the case, then I guess I have to mow more frequently. I'm now cutting perhaps 2/3 of the top blades (there are lower blades from each stem that are cut less severely). Is there a way to slow the growth? I only fertilized the area once using starter fertilizer when we reseeded these areas, some in last Fall and some this April.
    – Roc W.
    Commented Jun 17, 2021 at 15:03
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    Twelve percent of the seed was annual ryegrass, which should not even be in the mix, and only 2+ percent bluegrass confirms my analysis of the seed (should be ~25% bluegrass with rest split between fescue and perennial ryegrass). But, you've gone through a winter and I assume your minimum temps were below 0 F, so the annual grass should've died unless it seeded itself fairly heavily last fall. I have a lot of perennial ryegrass in my lawn and while it does grow faster than the fescue and bluegrass, it's nothing like you're experiencing. I think twice-weekly mowing may be your only solution.
    – Jurp
    Commented Jun 17, 2021 at 19:28
  • The only way I know of to slow the growth of lawngrass is a combination of high temperatures and no water - the grass will stop growing and after a time, go dormant. After maybe a month of dormancy it will begin to die, so this is not a long-term solution.
    – Jurp
    Commented Jun 17, 2021 at 19:29
  • Before I knew better to look at the actual seed composition, Scotts sounded like a reasonable name and those bags were ones I can find in large lbs. I still have two more bags I kept in stock for overseeding this Fall... With our relatively large lawn (1 acre), the more premium seeds quickly get expensive too, and difficult to water when planting.
    – Roc W.
    Commented Jun 17, 2021 at 19:57

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