My nephew may use our yard for a wedding in late August. My perennials are pretty much all toast by then. I'm thinking if I plant a whole slew of annuals, that could make a nice splash. I'm in the maritime Pacific NW, zone 8. August is dry and hot. I thought I'd try starting a bunch of annuals to pop in kind of everywhere, first cutting back all the spent perennial foliage. My experience with annuals is pretty slim. I'm thinking naturtiums and zinnias are pretty foolproof. Can't remember when the garden mums show up at the nurseries, but those may be an option as well. I'll have honeysuckle in bloom and Japanese maples, nandinas, and ninebark for foliage. I don't know the bride's taste, but I lean toward bold colors (oranges, reds, yellows) rather than pastels. Ideas? Neither of the couple strike me as too tweaky, although the bride does some sort of wedding planning so there's that.

I'm in a different climate so I wouldn't pretend to know the Pacific NW but is there a botanical garden near you? They might have recommendations.
Dahlias usually start by then for me if they are planted early enough, also pentas, marigold, coleus, petunia, lantana, bidens, purslane, scaevola, coreopsis, guara, angelonia, ageratum browallia, torenia, calibrachoa, cleome, begonia, impatiens, Diamond Frost euphorbia, diascia, geraniums, gomphrena, vinca, canna, sunflowers, caster bean, so many. You know what, go through the Proven Winners catalog. They focus on heavy bloomers or colorful leaves.
I do recommend using Miracle Gro Bloom Booster. I go lighter and less often than the label because I find too much MG burns the plants but I found that a couple of treatments kept my flowers in bloom.

Good idea on the Proven Winners, gave me good ideas. I've never done much with annuals but I'm thinking that may be the way to go.