Answer: You can plant sun loving annuals first thing in the spring and then replace them with shade loving annuals when the grapevines begin to shade the window boxes. I like this idea because you'll always have some fresh color in the boxes. Or, you can choose shade-loving, sun-tolerant perennials. Springtime sun is less intense than summer sun so these plants should do well in your windowboxes:
Annuals: begonia, coleus, impatiens, forget-me-nots (Myosotis sylvatica), pansy (Viola).
Perennials: astilbe, bleeding heart (Dicentra), bugbane (Cimicifuga), campanula, columbine (Aquilegia), coral bells (Heuchera), foxglove (Digitalis), goatsbeard (Aruncus), hellebore, daylily (Hemerocallis), hosta, Virginia bluebell (Mertensia pulmonarioides), fern, monkshood (Aconitum), phlox, primrose (Primula), lungwort (Pulmonaria), cardinal flower (Lobelia), Siberian iris, veronica
Groundcovers (for that trailing, cascading look): ajuga, wild ginger (Asarum), sweet woodruff (Galium odoratum ), epimedium, English ivy (Hedera helix), lamium, liriope, mondo grass (Ophiopogon japonicus), pachysandra, spirea, vinca.
Hope this gives you a few ideas!
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