Container sizes for burying these plants?

I have a border filled with awful water logged clay/debris filled in by the builders when my house was recently built. I've mixed in some top soil and compost but plants aren't thriving in this ground unsurprisingly (pictures taken before they started to wilt) I have lined above the clay and put white pebbles on top.
I'm going to dig up these young perennials and re-pot them under the gravel so they don't get waterlogged in the clay and stand some chance of survival/growth. What size containers would you suggest? Or would burying a plastic grow bag work better?
1. Erysimum red jep
2. Heuchera
3. Campanula lactiflora
All 3 were bought in 2 litre plastic pots a couple of weeks ago so they aren't very big at all yet.
Thank you!

 

Hi Leanne

I would go for 5 litre containers.....above ground level In other words placing them as attractive pot plants in their own right

However, there are plants that would thrive in those wet conditions.....astilbes for example. They have colourful early spring foliage, early summer feathery flowers and attractive foliage thereafter and enjoy wet conditions. There is a fantastic astilbe called Shogun that has amazing chocolate brown foliage. Astrantias too would do well there....pincushion flowers like little gems all summer long. Ferns too ....the Japanese painted ferns have wonderful bluish grey marbled foliage.....this would look sensational next to the aforementioned Shogun Astilbe. Also assorting well with these plants is a favourite grass of mine, hackonechloa, that would thrive there. Beautiful mounds that then cascade and move in the slightest breeze......yellow foliage, variegated foliage, green foliage and even some with red tints to them. Planting things such as these will save you an awful lot of maintenance and replanting and give you permanent enjoyment I think

 

I think ultimately you really need to improve the soil, I know clay can be a problem, but once you get it into a good condition its one of the best.

The plants you have put in, how long have they been planted? 2 weeks?
I suggest the root balls have dried out, once dry, they are difficult to re wet, and two weeks is not long enough for them to have rooted into the surrounding soil.

I'm slightly confused as you say water logged and wilting.