My first small garden design - help please!

Hi. I'm taking the Geoff Lawton online PDC right now and I've got a friend who I'm designing for as my design for the certificate. It's an interesting plot - she has a 9 year old walnut tree that can't be removed, so we've had to think about how to deal with the toxicity there. That's all been really interesting and I think we've got some really nice solutions. However, I still have a couple of issues I need to work out and I thought you guys might be able to offer some advice.

Firstly, I read somewhere that mulberries could help to shield against the effects of the walnut's juglone. Can anyone confirm if that's true?

Secondly, the client is interested in keeping ducks and wants to build a small pond for them, but the soil is only about 30cm deep and almost dead flat. Underneath that is a either the concrete roof of the underground garage or a layer of gravel. There is a slope of about 1:1 at a height of 45cm at the edge of the garage roof though, and cheap clay available locally. I wondered if it might be possible to build a dam wall directly on to the soil that's there (the soil is almost 100% clay right now) with a keyway going just 10-15cm down. Will that be safe if we seal the ground well inside? The wall would obviously only be about 45cm high.

Finally, if the pond seems like a plausible idea, what kind of plants can I grow there, either around the edges or in the water itself? Anything that can be either duck food or human food is great, but the client would like pretty things too. The garden is in southern Germany on the edge of Lake Constance. Temperatures there now are 25-30C, but they also get some of their heaviest rains in summer. Winters are pretty mild with only a few days of frost and very little snow. Local farms produce tons of carrots, tomatoes, squash, lettuces, apples, citrus, watermelons, corn, cherries and berries, amongst other things. She's interested in trying wild rice. Does that sound possible?

Any help is greatly appreciated. Thanks!

There are lists of plants that do well with Persian walnut I believe it's juglans regia ? sp I would do that on a search. Make sure you don't have black walnut-much tougher to deal with.
John S
PDX OR

Kenny, could you give an idea how many meters square the area is?
I'm not good at envisioning designs without pictures, and I haven't created ponds so I'll leave that alone
Checking the client is familiar with ducks? More to the point, what a mess they can make-
especially in and around small, passive water bodies...
I've seen people's visions of happy ducks on a pond evaporate
when the ducks decide to set up camp outside the back door.
Nothing like slipping over on duck crap is to burst your bubble

It's English walnut, but I'm told a lot of English walnut is now grown on black walnut stock. Either way, we're assuming the worst. The rules of the community say you can't cut down the major tree in the garden though, so unless we could easily pretend it was diseased or falling down anyway, we're stuck with it. I don't mind too much. It's been interesting to learn about it and try to find some solutions.

The total size of the garden is just under 250m2. And yes, I'm pretty confident in the client's ability to manage the ducks and their crap!

I think I remember huckleberry shielding the effects of juglone. Don't have gaia's garden at the moment, but it's in there.

Anyway you can find plants growing under a walnut, so the weight of the assertion that juglone is a problem we should seriously consider in our designs is up for debate. It might be more of a problem in walnut groves where the juglone is very high and toxic. One tree probably doesn't put out that much. If you space them enough you could have multiple walnut trees growing happily next to other things.
William

Juglone affects Heath family species the most. Huckleberry would be in that family, so this would seem unlikely.

Black Walnut puts out a lot of juglone compared to other species, and this is the list of what grows under it in the US.
http://www.hort.purdue.edu/ext/HO-193.pdf

http://www.groworganic.com/organic-gardening/articles/companion-plants-that-tolerate-black-walnut-tree-toxicity

Found it.

Wolfberry, hackberry (knew it was an h-berry!!), elderberry, eleagnus, currents, mulberry, tomato-pepper-nightshade.

There's Toby's solution to walnuts and juglone.
William

Thanks William. I think you make an interesting point about how toxic juglone can be. In such a small garden with such shallow soils though, I think it makes sense to take all the action I can to shield against it. Thankfully many of the plants the client is keen to grow (or keep in a few cases) are juglone-tolerant anyway. The mulberry idea seemed like a neat way of combining a great fruit with a way of helping the garden develop well regardless of the walnut.