Why are Knock Outs not Blooming?
Figuring out how to get Knock Out roses to bloom means finding out what’s causing them not to flower in the first place.
Animal pests
Are buds on the roses one day and by the next morning totally gone? Maybe they’re lying on the ground as if cut off, or perhaps missing all together. The culprits here are usually squirrels, deer, or elk. Deer and elk may eat just the buds off first with a small amount of foliage, returning another night to decimate the bush. I am not sure why squirrels will sometimes cut the blooms off, leaving them lying about and not eating them. Perhaps, their plan is to come back later for them. The use of a liquid or granular repellent may give some relief but you need to keep on top of applying the products for them to work their best. That said, these repellents can work well for the squirrels and rabbits too if they are eating the foliage. Building a fence around the rose bed or garden can help, but many times it must be an electric fence to be very successful, as hungry deer and elk will either jump over the fence or push it down in places.
Insects
Tiny insects, such as thrips, can bore into rosebuds and will cause them to fall off without blooming. To truly get at such insects, one must use a systemic insecticide listed for their control.
Light
If Knock Out roses won’t bloom, they may not be getting enough sunlight. Make sure when planting them that they get 6 to 8 hours of sun. Take a good look at the proposed area for planting at different times of day to see if any trees or buildings shade the area. Some shade where partial sun is available can be a good thing during those hotter days of summer, as it provides some relief from the intense sun and extreme heat.
Fertilizer
Be sure to feed your roses with fertilizers that build the soil or root zone of your Knock Out roses as well as feed the upper parts of the rosebushes. Repeated high nitrogen usage will cause major foliage production with little to no blooms on Knock Out roses. High nitrogen fertilizers can also be the cause of a condition called “Crooked Neck” on roses. The forming bud tilts to one side, sometimes drastically. The bud may open and the bloom crooked and malformed, or may not bloom at all.
Water
Along with the proper feeding, make sure your roses are watered well. Lack of water, especially on hot summer days, doubles down on the stress factor the rosebushes must deal with. Stresses and shock will cause Knock Out roses to stop blooming and become more susceptible to fungal or disease attacks.
Disease
Fungi such as black spot, powdery mildew, and rust will stress rosebushes and stop the blooming process even in the formed buds stage. Spraying roses on a scheduled basis with a fungicide may be in order. There are many no-spray gardens out there that are lovely and perform very well. In the no-spray gardens, one must be very careful to obtain rosebushes that have been proven to be high in disease resistance in varying weather conditions/climatic conditions. In my rose gardens, I have chosen to use a very good earth-friendly commercial fungicide. Using the product at the rate noted on the label will indeed cure any fungal problems. Choosing earth-friendly products to spray for any pest problem as a first choice is best, as harsh chemical sprays can simply add to the overall stress, thus limiting bloom production.
Deadheading
Even though one of the big selling points for Knock Out rosebushes is that they are self-cleaning, trimming off the old spent blooms “precisely” below the base of the old bloom will encourage bloom production.
