Sad to lose a plant despite your efforts at staking. I came home to find the first 'tipper' lying on the ground yesterday too. The large blooms tend to be heavy and, if wet from rain, even heavier. Add a gust of wind and it can be disaster. There are plenty of larger bushes or tall ones that get two stakes here- heavy duty metal posts to which I anchor the whole plant as it grows bigger. It also helps to encircle the plant with ties as high as you can to support the plant as it grows. This can be unsightly, but better looking than a prostrate plant.

There are plenty of posts on digging and storing- check back in about September/October from any year and you will find them. Or check the link for great information and photos.

Here is a link that might be useful: Digging dahlias