The shoots on my penstemon plants turned brown, wilted and died off, can you give a reason for this and how to prevent it happening again?
The plants have most probably been affected by a wilt disease.
These tend to be soil-borne infections, gaining entry through roots that perhaps have been damaged by hoeing.
There is no real effective control, apart from removing the plant/s and some of the surrounding soil.
You could try spraying the plants with a systemic fungicide early on in the year as the new growth commences, failing that you will have to resort to the method described above.