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I would really appreciate some planting advice, but have to embark on a long explanation first! Bear with me, I'm a novice.

My garden also serves as the roof of a Grade 1 listed grotto (the Shell Grotto in Margate). It is largely laid to lawn, under which sit French drains. This was deemed by English Heritage to offer the best protection from water ingress for the Grotto which is cut from the chalk bedrock (the apex of its ceiling is only a few feet below ground level).

The garden is on a slope and there is little topsoil above the drainage; what there is is alkaline.

We have a flint wall running along one boundary and I would like to create a border along it. This area is in almost full shade and the soil is pretty heavy. It's very close to the Grotto, although not directly over it. What plants to use? Obviously nothing with invasive roots! And ideally I would like to introduce plants that assist with keeping the Grotto dry. A visitor yesterday suggested that irises are great for sucking up damp - would they suffer the shade?

Ideally, I'd love a bank of hydrangeas, or rhododendrons or anything that my other half considers to be 'old lady plants'. But the Grotto might take priority over my wistful longings for a cottage garden!

I'd be grateful for any suggestions. 



Could you show us photos? especially the proximity of the flower bed to the grotto?

I can't show you the proximity of the Grotto to the bed can see one or the other but not both! However, here's my best attempt to explain...drainage going in and then turf being laid, first view looking downhill, second view uphill. Blue lines indicate line of bed; red lines are where the Grotto passages are underground.


 And then is part of what is underground:

 Does that help any?



Wow, Sarah, am speechless; what an amazing place. As you say, you are limited to plants that don't have very deep roots. Have you done a soil test yet to find out the ph?

I will try to keep 'bumping ' this thread so that other, wiser heads can help



If there's chalk bedrock, it's likely that the soil will be alkaline.  You've not got much depth of soil - I'd look at shade tolerant alpines - ajuga, aquilegia, campanulas,  epimedium, tiarella, hardy ferns, lysimachia and violas.  You'd probably find that foxgloves would look lovely with that lot, and would be happy in those conditions. 

Thanks all, thanks artjak. Sorry to have taken so long to reply - clicked the 'email me' box and haven't had an email.

Anyway, yes alkaline soil. Should I ph test? Will that tell me anything extra?

Edd - you really don't want a grotto. Not one under a garden anyway. You become obsessive about the weather and die a little every time there's a downpour.

Dovefromabove - thanks for the suggestions. The garden is inundated with snails. Am I right in thinking that they love foxglove? I really would like lots of height - without extensive roots. I miss trees.

Anyone vouch for the view that irises would tolerate the conditions whilst sucking up loads of water?

Thanks so much for the help.



Sarah, the email function has not worked for about a year; just keep checking 'followed threads'.

You could also try Hollyhocks for height, though it is difficult to get the single variety except in almost black; I find the doubles look rather like pom-poms. Cosmos also grows pretty tall also Verbena Bonarienses.

Good luck with it and post some pics later in the season

Steve 309

You don't want rhododendrons in shallow chalky soil - they want acid and are large, woody and invasive.  Yuk!  (Well, I don't, anyway!)  How about a climber up the wall - they may be more shallow rooted than foxgloves etc.  I dug out a foxglove t'other day (I like them but it was getting in the way of the veg bed) whose root was about 18" long.  I suspect the same might be true of hollyhocks, though I've never grown them.

Edd - of course it's haunted! The Blue Lady walks the Serpentine Passage. Apparently. The info in your link seems to back up irises being thirsty. I had done some Googling, but it's easy to get brain fog when you're reading around a subject that is alien to you. Well, easy for me!

Have added your suggestions to my list artjak, thanks.

Rhododendrons off the list then. Must I give up on my dream of a bank of hydrangeas too?


Steve 309

I suppose you could change the soil by adding lots of acid compost or pine needles or similar - but might the leachate damage the (presumably lime) mortar underneath?  Why fight nature anyway?

I'm not an expert but I think hydrangeas will grow in alkaline soil and give you pink (or blue?) flowers instead of blue (or pink?).  (See - I said I wasn't an expert )  But again, I'd be worried about the depth of the roots and damaging the drains and roof of the grotto.

Maybe lime mortar is the reason the soil is alkaline?

Heather Michaels

What a fantastic place to live Sarah, I'm so jealous! The closest thing I have to a grotto is a coal bunker


Please do not try to change the ph of the soil; you will be cruisin' for a bruisin' Much easier and more ecological to work with what you have, all serious gardening books advise this.

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