A weigela full sun spot is what you want. Plant it in 6 or more hours of direct sun and you get the heaviest bloom and the deepest leaf color. It also works as a partial shade shrub, but you trade away flowers for that shade. So give your weigela sun first, and treat shade as a backup plan.
I moved a 'Wine and Roses' into a shadier zone 5 bed by the back fence, tucked behind a tall lilac. Within a season the purple leaves faded to a muddy green. The flowers thinned to a scatter of pink along the stems. So I dug it back into the open lawn edge where it caught the morning sun. By the next June the leaves came back deep wine-red. The branches were crowded with blooms again.
Full sun means 6 or more hours of direct sun each day, and your weigela does best when that light lands through the morning and into the early afternoon. That much sun is what pushes the shrub to set the most flower buds. In partial shade, which runs about 3 to 6 hours of sun, you still get a healthy plant with good structure. It just carries far fewer blooms, and the show turns thin and patchy. Drop below 3 hours and you may see almost no flowers at all.
Leaf color depends on light even more than the flowers do. The purple-leaf and variegated cultivars need full sun to hold their color all season. Without it, purple fades toward green and crisp white edges wash out to a dull cream. My 'Wine and Roses' is the classic example, and 'My Monet' with its pink-and-cream leaves reacts the same way. If you love those colorful leaves, you have to give them the light. Green-leaf types are more forgiving, since they have no special color to lose in the first place.
Some of the dwarf forms handle a touch more shade than the big standard types. Compact picks like 'Midnight Wine' stay tidy and still flower with a bit less direct light. They make a good choice for a spot that gets bright sun for only part of the day. Even so, you get the best result by nudging them toward the brightest corner you have rather than the darkest. None of these shrubs are true shade lovers, no matter how small they stay.
Heat helps too, as long as the roots stay watered. A weigela full sun planting in the South still does fine, and the extra warmth often deepens the flower color. Just give it a good soak in the first couple of summers while it settles in. Mulch the base with a couple of inches of bark. The mulch keeps the roots cool and damp. That simple step stops the wilting that scares some gardeners away from sunny spots, and your shrub stays happy through a hot week.
If strong weigela flowering and rich foliage matter to you, hand the plant the sunniest spot in your yard. Watch the bed across a full day before you dig. Pick the place that bakes in light from breakfast through lunch, and skip the shady pocket under a tree or on the north side of a wall. Give your shrub that open sun and it rewards you with arching stems packed in pink, red, or white each spring. Choose a shady site only when you truly have no sunny ground left to spare in the yard.
Read the full article: Weigela Shrub Care, Pruning and Varieties
