Overwatering Wallflowers (Erysimum 'Bowles Mauve')?

I am new to gardening and doing it in containers on my tiny, mostly shaded, porch on the north side of the house. The space gets a good dose of late afternoon sun and misses most of the rain in Seattle as it is well under the house's eaves. I'm having mostly good luck except that my Erysimum 'Bowles Mauve' is looking bad at the base (see image) like I am over watering it maybe?

Appreciate the benefit of your wisdom!

 

looks like the top is just shading out the bottom

 

hello there...i work for the royal parks and grow a lot of erysimums we too get top heavy plants ..try pruning out the centre forcing new shoots..and don't allow to become straggly..keep an eye on them!!