Lawn with thick thatch

phcoreilly · March 2023

We have a big area of lawn which is very ropy.
There's a very thick layer of thatch about 10-15cm deep.
I've tried raking with a hand rake and an electric raker. Also tried top dressing and over seeding. It's all as bad as ever.
Just wondering whether to get some machine (turf cutter?) to take up all the grass and thatch and starting from scratch.

Any advice or thoughts most welcome.

Fairygirl · March 2023

Have you a photo @phcoreilly? It sounds like an awfully large amount. Do you collect the cuttings when you mow? Is it a shady or sunny site?

The surroundings can also have an effect on how well grass thrives, so it's important to know what sort of general regime you have with the grass - how often you cut, how short, general climate etc. That would have a bearing on whether your start again or not

phcoreilly · March 2023

Fairygirl said:

Have you a photo @phcoreilly? It sounds like an awfully large amount. Do you collect the cuttings when you mow? Is it a shady or sunny site?

The surroundings can also have an effect on how well grass thrives, so it's important to know what sort of general regime you have with the grass - how often you cut, how short, general climate etc. That would have a bearing on whether your start again or not

We only been in the house two years and it was like that when we arrived. I don't mow it very often as the grass doesn't grow much. I've n ever treated it other than rake, top dressing and over seeding.
I've never seen thatch as deep as this. It's like walking on a sponge. I've no idea how it got like that.

Dovefromabove · March 2023

10-15cm or 10-15mm?

JennyJ · March 2023

10-15cm of thatch (4-6 inches in old money) is extremely unusual. Can you post some pics? If you could stick a spade in and cut a piece out to get a cross-section pic that would be really helpful (just tread the lifted piece of turf back afterwards, it won't know it had been moved).

10-15mm (about half an inch) is quite normal for a lawn that's been neglected and an electric scarifier should be able to tackle it. I find that the type with wire tines is best for pulling out thatch. The blade type is for cutting slits for aeration although it does pull some thatch out.

bédé · March 2023

My approach would be chemical (excuse the word). Forget all the hard, and possibly expensive work.

What your lawn needs is to accelerate the natural decay of the dead grass and probably moss. What will help is: water, nitrogen-rich fertiliser, possibly raising the pH, and possiblly moss-killing.

I have found that the Sulphate of Iron that I use to control moss in my lawn, also accelates the decompostion of dead grass. I use 6 tablespoons of FeSO4 in a 1.5 gallon watering can. To a fine lawn I apply at the rate of 3 watering cans to 100m2 2x a year. I would suggest you try this and possibly repeat in a month's time.

Nitogen fertiliser applied a week later would be a good idea to feed the grass and feed the bacteria that rot the dead moss and thatch. A top dressing of good soil &/or compost would be worthwhile. Growmore would be the best value (I wouldn't advise applying it to a fine lawn in dry weather).

Scarifying does a lot of damage. Raking spreads the moss spores about, and removes a good source of in situ peat/humus. Reseeding is a waste of time and money if done on top of thatched, dry lawn.

Yours is the only situation where I would recommend seting your mower at its lowest setting. The removed stuff will make good compost.

bédé · March 2023

PS.

I have added more to the above. It is from my practical experience.

The correct amount of FeSO4 is 6 tablespoonfulls. (I have a bigger spoon I keep just for the job - I apologise for not using metric measures throughout.)

A few trial holes to check on what your lawn is growing would be a good idea.

Although professionals don't like it, I have found that normal humans actually like a springy turf.

JennyJ · March 2023

Bédé, how do you go about composting thatch? I find it takes ages to break down, much longer than everything else in the compost bin, so I generally put it in the council waste (occasionally I use some to fill out the base of deep pots that I'm going to put shallow-rooted plants into). My thatch is mostly dead grass with only a little bit of moss and I usually scarify in autumn to get rid of the aftermath of summer dryness, which results in the grass making a good recovery in October and November before winter sets in, and it starts the new season pretty much thatch-free so I can overseed any thin areas. I don't want add nitrogen-rich stuff to the lawn in the autumn and I don't want to leave the dead stuff all winter so I don't think the rotting-down-in-situ approach would work for me.

Fairygirl · March 2023

I think @phcoreilly needs to answer the questions we've asked.
ie -the correct depth of the thatch and the other conditions.
If the thatch is left in situ and then top dressed and seeded, it'll more than likely just stay spongy. If it's not being removed, and it really is 4 - 6 inches, grass will struggle to grow, and cutting it means it'll be swamped by the thatch.
If the area is mossy, and it could easily be that rather than thatch, that needs treated.

This is why photos help so much.

bédé · March 2023

Jenny, to answer your specific questions, but others may be interested:

Thatch is usually dry. If not it should ideally be wetted before adding to your compost bin, I don't . (I have a ca 6m3 open to rain "heap" on 1-2 year cycle).

You've read my views on scarifying, it's hard work to do properly and better to rot it in situ, and not spread moss spores about.

I usually use a slow release fertiliser (Scotts). Autumn grade in ca October and summer grade March plus. The nitogen is never in excess. I buy cheapest Growmore and scatter this sometimes if rain is due, or water if it hasn't happened). If done in the dry you can get scorched spots - not a problem with a restoration project.

The rotting down amount is minimal on an already fine(ish) lawn. It works fastest if wet and warm, so it's a spring, watered-summer, or autumn activity. With a well-maintained lawn the rotting is happening naturally and continuously; perhaps not so fast on an acid soil.

Spiking I do when it's needed. Not often on a sandy soil.

Timing is personal, for me it's usually when-I'm-in-mood.

JennyJ · March 2023

Thanks for the clarification Bédé. I think I'll stick with my current routine. I have a machine for scarifying so it's not hard work for me (and that's speaking as a small-ish puny person

) and there's never much moss so spore-spreading isn't a problem here. Even wet and mixed with green stuff I find thatch (dead dry grass mostly) takes ages to decompose so the council can have it for commercial-scale composting.

Lawn with thick thatch

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