At the end of the season last summer here in St. Paul, Minnesota, I noticed a large quantity of black powder at the base of my 4 ft x 3 ft patch of blacked-eyed Susan plants. It looked as though black 'coal dust' had been laced throughout the patch, from the ground and up about 8 inches. Any ideas what would cause this and how would I keep it from happening again? They are planted in the middle of a 20 x 10 foot garden, receive a lot of sun, are planted in black dirt, and the garden has cedar chips sprinkled on top of the dirt.
That is called sooty mold. This article will help you in case it comes back:
How can I get rid of the black spots on the leaves of my black-eyed Susans? The spots grow until the whole leaf turns black. How do I keep it from spreading? Is there a way to get rid of them, and how do I prevent them in the future?
This sounds like black spot fungus. You can treat the plants with a fungicide and it should take care of the fungus. If you are manually watering them, try to water them from below rather than from above. The fungus is made worse by water sitting on the leaves.
Lower leaves of Rudbeckia (black eyed Susan's) have black spots on them. We have had unusual amounts of rain this spring. Could this be part of the problem?
Yes, the additional rain is the cause. These plants tend to grow close together, which means there is not much air flow to begin with. The additional moisture from the rain makes them far more susceptible to fungus.
A standard fungicide sprayed on the plants will help clear up the problem. You may want to consider dividing some of the plants if they are growing close together.
I've had Black-eyed Susan's along the side of my house for years; and about three years ago. I noticed the leaves turning black. They didn't get as tall and the flowers didn't get as big. The leaves get black spots, then the entire leaf gets covered, dries up and dies. There are way few flowers now. Used to get lots of flowers. Are they just old? Do they have a blight or a bug?
It sounds like your black-eyed Susan's have a mildew or fungus. Make sure you clean the bed out thoroughly this fall and dispose of all the material by burning. In the meantime, treat your plants with an all purpose fungicide, or neem oil. As our gardens grow, changes take place that we never notice. Do your plants get the same air circulation they used to, the same sun? Maybe it's time to find a new home for your black-eyed Susan's and a new plant for the side of your house.
I have a beautiful bed of rudbeckia - the black-eyed Susan variety. They bloom profusely in the early summer; however, from that point on, they tend to send up very short stems from clusters of leaves, and the flowers do not mature. The petals remain green and the flowers small. How should I be deadheading them, and what is the reason for this type of issue occurring?
These are young seedlings that were sown the previous year. You can deadhead if you choose, but it isn't necessary.
We moved into our home 3 years ago and soon noticed a problem with the plants we brought with us from our other home 30 miles away. It started with the Black-eyed Susans getting spots. It has escalated to the roses not having leaves and the flowering crab trees dying, one each year. The current tree has very few leaves left. We are also having an enormous problem with Japaneese beetles now, too. But that's another issue. . .
One of the very best fungicides against the black spot fungus that I know of is called Mancozeb. I get mine from an online store called http://www.rosemania.com . It will leave a little bit of yellowish powdery residue on the foliage but that is part of how it works. As for the Japanese Beetles, they can be a very tough customer. Start putting down some stuff called Milky spore now and in a few years it will be built up enough to really make an impact. Until it does, try using some Bayer Tree and Shrub granules. Since you are not talking about fruit trees, the Bayer product is great at getting to the bug problems. I use it once a year for my trees and other shrubs, it does a very good job for me.
I have moss growing in my perennial garden. What can I do to get rid of it? The moss mainly grows right by my black eyed Susan.
This article will help you with this: https://www.gardeningknowhow.com/ornamental/foliage/moss/moss-on-plants.htm