I am partial to zinnias, and I was going to suggest zinnias as colorful and long blooming, but since you say "Part of the issue is its a weekend place so I'm not there to water frequently" I am going to suggest Portulaca (Moss Rose) instead. Their leaves have the appearance of a succulent, but they bloom over an long period and they are tolerant of being neglected, waterwise. There are several strains of Portulaca to pick from -- some have single blooms while others are double. The Portulaca strain Happy Trails has a trailing plant habit that is useful for filling in blank spaces. There are many portulaca strains available, some in mixed colors, and some in separate colors. Like zinnias, all colors but blue.

ZM (not associated with any product or vendor mentioned or linked)

I too suggest portulacca. they are about the same height as impatiens. They will self seed so you may just have to move them around next year.

The blooms won't open on gloomy days, though...

Have you considered perennials and small shrubs rather than annuals? Perennials could provide a succession of colours and shapes all year, including spring bulbs, or some of your wonderful woodland natives like Trilliums. They would be weed suppressing and low maintenance. The site looks wonderfully woodsy and natural so annuals would seem rather suburban in the context. Plus they need purchasing and planting every year, disaster could strike a mass planting of one thing and, as you mention, there is a water issue.

I have but perennials generally don't bloom as long as annuals and even though in the long run they are less expensive than planting every year, I do like the variety annuals give me to change things up every year like color combinations. I have also planted portulacca at my main home in the past with mixed results. Thank you all for your comments!

Portulaca is a good choice for dry sunny areas. Its pretty care free - but - deer like to munch on it. I have to spray mine with a deer deterrent.

The "profusion" dahlias are great. they don't need much water and bloom like crazy all summer. They are usually a bright orange, a yellow and a pinkish, the orangish is the absolute best. the pinkish seem to fade. I LOVE them. they get real bushy too and fill in a lot of area. Thinking they are 8-10 inches tall. I get the Profusion Orange every year.

Another option would be to get annuals that reseed easily. That helps a bit on not having to replant every year and eventually, the naturalized look will have its benefits also, not just nicely placed new plants in a landscape design.

morning glories reseed like crazy. And they are beautiful and in different colors.

Sorry, those are called "profusion zinnias" not dahlias. Look them up on google. they are so nice and get so bushy too.