Knockout roses leaves are yellow, now brown and not growing

Asked July 6, 2020, 2:49 PM EDT

Hello I live in dc and I have 3 knockout rose bushes at the front of my home. The two in the side are happy and vibriant but the one in the middle is not growing, has yellow and now brown leaves. Around march/April all three were blooming and growing beautifully but lots of rain came late April to almost all of June. About late june is when I noticed the middle bush had yellow leaves. I thought maybe it was mold (found some black mushrooms at the bottom of the middle bush) so i trimmed the yellow leaves and clean up the mulch so the middle bush can have some more circulation. That didnt help. Is there anything I can do to revive my knockout rose bush? Somethings to note: I mulched this year but didn't get a chance last year. All three bushes get afternoon sun from about 1245 to 420. They are about 13 years old and normally they grow in abundance. There are spider mites but there arent too many. Any suggestions on what I can do to save the bush or what to do and hopefully I didnt kill it, I would be very grateful.

District of Columbia County District of Columbia

4 Responses

We viewed the photos. In general, knockout roses grow best in full sun in a well drained soil. There is not enough spacing and sunlight for the middle shrub and it will not thrive between the two larger shrubs. There is a lot of competition for moisture and nutrients and lack of sunlight in its location. Check the soil drainage in the area. They do not like a poorly drained soil.

Also, there is excessive mulch around the base of the roses. Excessive mulch reduces soil oxygen for roots, suffocating them and causing them to die. Roots in search of oxygen and water sometimes grow into excess mulch. During dry periods the mulch dries out and the roots in the mulch die.
Make sure mulch is no thicker than several inches and keep the mulch away from the base of the stems. https://extension.umd.edu/hgic/topics/excess-mulch

It looks like the middle shrub will continue to decline. It would be best to remove the middle shrub and this will provide more air circulation, moisture, and nutrients for the other two roses. Knockout roses can grow to about 4 feet by 4 feet or more.
Here is a good article on Knockout roses https://extension.umd.edu/hgic/topics/rose-rosenot-always-look-%E2%80%98knockout%E2%80%99-landscape-roses

Marian


Would it be helpful to apply fertilizer just to give it some more nutrients? If so, can you recommend one?

this is the first year the middle rose bush has declined and it does get a lot of sunlight in the afternoon.

I meant to add Thank you for your advice. It is very much appreciated. I checked drainage and i think its fine but i will figure out relocation and removing some mulch.

I just wanted to know: for the time being, is adding fertilizer something i can do to make sure the bush doesn't completely die on me before i can move it?

thank you.

Fertilizer will not help the ailing shrub because it cannot make use of it - the roots have been too damaged or too much top growth has died back and isn't healthy enough to respond to more nutrients. Mature shrubs typically don't need any supplemental fertilizer in general; while roses can benefit, these not being in full sun are not growing to their full potential and thus do not need a boost from added nutrients. (The sunlight is the limiting factor, not nutrition.)

Roses need a minimum of 6-8 hours of sun a day to thrive, though they will tolerate less with weakened vigor and less bloom. It sounds like these are only getting 3-and-a-half hours of direct sun, so they will likely continue to struggle long-term. The weather patterns of the past two years (springs with excessively wet weather, and a late-season drought last year) may have been the final straw for the shrub in the middle, since it had the extra stress factor of competition from its two neighbors.

Miri