It's called Impatiens Downy Mildew; I haven't grown them since 2013. They start off okay but by the end of July, the leaves all fell off and the plant shrivelled away to nothing. You'll know you have it if you look at the underside of the leaf and it's powdery white. I read that once the spores are in the soil, you can't grow any more impatiens there for many years.

ks, some good pictures would help us identify a problem.

Impatiens Downy Mildew is a world wide fungus-like pathogen for which there is no cure. Even the growers are finding it difficult to impossible to prevent.

The propagules remain in the soil, can be carried in wind currents, are brought in from the garden centers, and are found in the greenhouses of the bedding plant growers. Even the seeds that we buy can be infected.

Scientists have recommended avoiding Impatiens walleriana entirely until plant breeders are able to come up with a resistant shade loving cultivar.

BUT, we don't know if that's what your issue is but it does seem likely.

Yes. I should have included a picture which I'll do now. After looking under the leaves, I guess I don't think Downy Mildew is the problem. They plants look healthy, and yes they are blooming some. They're just not full and dense as they should be by late August (or early July, even). This should be a solid wall of plants and blossoms, but instead, it's looking scraggly and unimpressive.

Could be sun related- I have a bed that is somewhat shaded, and there is a definite difference in the amount of flowers, and size of plant.

where are you ... when were they planted ... did you have an extended cold spring???.. were they plugs or seed started ...

you havent given us much to guess on ...

ken

I'm in NE KS, they were planted as plugs around May 1. No, we have not had unusual weather. The site and planting pattern hasn't changed in 15 years, but the impatiens have performed poorly the last 2-3.

ks, it is difficult to pinpoint the symptoms of IDM; it can present itself in many different ways. Just so you know, a slow decline can be an indicator.

Another thing to think about is that trees can compete with other plants for valuable resources both above and below ground. You're thinking of shade but you should also consider competition for water, soil oxygen, dissolved nutrients, and even underground space.

As the trees have matured over the years, both above and below ground, perhaps they are winning the battle for all of these things......trees usually do come out on top.

One more thing! Many tree species produce allelopathic chemicals that can affect the health of some plants growing near them. Do you know what kind of tree is casting the shade?

There are at least 3 trees casting shade. 2 are huckleberries, 1 is an ash. They're probably 50 or more years old (I live in the house I grew up in and they're older than my memory!