Any pot of that weight will most likely sink into wet muddy grass. As @nutcutlet suggested, a slab base and then pot feet/bricks would allow the pot to drain whilst distributing the weight over a greater area. Depending on how wet the grass is, it may still settle/sink.
Why does it need to be sited on the grass though? It'll need a lot more attention in a pot too. However, any pot that sort of size and weight will sink if kept on grass. The only foolproof method would be to dig out an area of turf, plus soil, to about 6 inches depth and fill it with concrete, or gravel with a paving slab on top, to make a reliably solid base for the pot. Then raise it on bricks or pot feet depending on what suits best. You don't have to use shop bought feet for pots.
It's a place where beautiful isn't enough of a word....
I live in west central Scotland - not where that photo is...
If you don't want the pot to sink into the grass you are going to have to use a paving slab, and then put the pot on feet on the paving slab. The feet help stop the pot becoming waterlogged.
I just notices you said the pot could weigh 30kg. I'm not sure pot feet will support that kind of weight.
Another option to distribute the weight would be to get some steel rebar driven into the lawn to create feet for the pot and keep it elevated...at 30kg you'll need at least six I reckon. It's in principle the same ideal as pile driving for tall buildings just in miniature. I used the method to keep an assemblage of pots on a garden bed stable and not sinking in.
I'd get some of these to put it on. They're deck blocks, intended to support a deck without pouring concrete footings. So they should hold up your pot well. Since they aren't flat on top drainage shouldn't be an issue
30kg is certainly a weight!! I'd assumed a lot less than that, but should have asked the question.
My heavy planters I keep OFF the grass, or at least, on circular paving slabs sunk in the lawn at strategic locations. They are then raised up further on bricks, some split lengthwise.
I refuse to use concrete blocks, such as breeze blocks. They have a tendency to disintegrate in the colder weather, in my experience.
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I don’t want to plant it in soil as I don’t want it to grow a lot more
thanks
However, any pot that sort of size and weight will sink if kept on grass. The only foolproof method would be to dig out an area of turf, plus soil, to about 6 inches depth and fill it with concrete, or gravel with a paving slab on top, to make a reliably solid base for the pot. Then raise it on bricks or pot feet depending on what suits best. You don't have to use shop bought feet for pots.
I live in west central Scotland - not where that photo is...
My heavy planters I keep OFF the grass, or at least, on circular paving slabs sunk in the lawn at strategic locations. They are then raised up further on bricks, some split lengthwise.
I refuse to use concrete blocks, such as breeze blocks. They have a tendency to disintegrate in the colder weather, in my experience.