Knockout Roses won't grow

Asked February 17, 2018, 12:48 PM EST

Hi, I have had knockout roses on south side of my home for 4 yrs and they refuse to grow. They aren't dead; they just are wimpy and pathetic. I have increased the water, decreased the water, fertilized them and checked them for infections (never have any signs of infection). My knockout roses everywhere else (west side and north side of house) are doing great.
Any thoughts or can someone come out to my house to look at the area?
Thank you!

Arapahoe County Colorado

3 Responses

Unfortunately, there many reasons why roses fail to thrive, and it’s a process of elimination. Assuming that all the roses were purchased together, planted at the same time and have been problematic every year since planting 4 years ago, this likely points to a soil, planting or site issue. Likely factors are:

  • Soil condition: There’s no mention how far away these are from the side of your home. Soil next to houses and foundations is very bad and must be amended before planting. Consider getting both a soil test and a pH test on that soil in which the roses are planted. Look especially for levels of Phosphorus and Potassium and the pH of the soil.

  • Soil and planting hole preparation: Soils must be amended with organic matter before planting. Our soils tend to be clay, which collects water and prevents good drainage. Sloping sites can have water retention issues. Roots sitting in water, especially stagnated water, result in poor growth. Never plant a rose in a hole the same size as its container. The planting area should be loosened at least 36" wide and 18" deep. Roses should be planted at soil level or slightly deeper (1 to 2 inches).

  • Soil compaction: Roses do not like to be trampled on. If these are in an area that gets foot traffic, roots will respond negatively to the stress.

  • Environment: Roses do not like to compete with the roots of larger plants such as trees and shrubs.

  • Roots: Sometimes roses fail to grow due to poor root establishment. Container roses can be pot-bound, so roots should be loosened prior to planting. The roots may be circling in the ground, rather than growing into the surrounding soil. These circling roots fail to give the plant vigor, and also fail to uptake the nutrients available in the soil or from fertilization. Unfortunately, the only way determine what the roots are doing is to dig it up and look. Despite what instructions say, never plant roses in their ‘bio-degradable’ container.

  • Fertilization: Always fertilize with a balanced rose food: Nitrogen (for strong canes, good blooms and healthy foliage), Phosphorus (for healthy roots and flower development), and Potassium (for root growth, bloom color and an overall vigor). The first fertilization should take place in late April (or after spring pruning), then about every 6 weeks until mid-August.

  • Pruning: Pruning promotes growth. Roses should be pruned in late April or early May after the danger of frost has passed.

  • Water: When watering, use a moisture meter to check soil moisture or feel down into the top 3 inches of soil around the rose. If it's dry, the rose needs water. If your roses are on an automated drip system, verify the system is working properly. Roses also need water during the winter months when there is no snow cover, and especially when located on south or west locations where it is warmer.

  • Sunlight: Roses need at least 6-8 hours of full sun each day. Sometimes we don't notice if nearby trees or other landscape plants have matured and the roses begin to get less sun than they need, resulting in poor growth.

  • Mulch: Roses need mulch to help keep soil temperature cooler during hot periods. This gives them a more consistent growing climate and helps to conserve soil moisture. Apply organic mulch to a depth of 3 inches, but do not let the mulch come into contact with the base of the plant.

There is not an easy answer to your question and it may be one or several factors. Use this list to help narrow down possibilities. After the soil/pH test, and the roses have been pruned, fertilized and are growing, if the problem persists, send us photos of them. This is especially helpful so we can see their growing environment in relation to other things that may be going on.

Thank you for your response Donnetta. I reviewed each of the items you mentioned.
These roses were purchased from and planted by a well known and reputable landscaping company in Denver. I was present to observe the planting and soil preparation as the company did it. They amended the soil prior to planting. I have included some pictures so you can see how far away from the foundation they are (the first two pictures have a red line around the roses in question). The landscaping company dug adequate sized holes and they planted each rose 1-2 inches below soil level. The area is not trampled on and I don't believe they are competing with the roots of larger plants such as trees and shrubs. The lavender plants are several feet behind the roses and the boxwoods are at least 4-5 feet behind the roses up against the patio (the boxwoods are the plants covered in burlap in the pictures). The roses weren't in containers when purchased, but were bare roots in soil/bags, so I can't imagine that the roots are circling. As far as fertilization, I am doing exactly as you mentioned: every 6 weeks from April-August with a balanced rose food. l prune all roses on Mother's Day each year, but there isn't much to prune on these particular roses since they don't grow. They are watered by an automated drip system and I frequently check the drips to make sure they are functioning and I check the soil moisture and they seem to be getting adequate water. This past summer I wondered if they were getting too much water so I even turned down the amount of water they were getting. It made no difference in their growth/appearance. I have been winter watering if there is no snow every 2.5-3 weeks. They are on the south side of the house so they get at least 6-8 hours of full sun each day. I keep them mulched.
The roses that were in this bed before we relandscaped the bed grew just fine, so maybe it is the actual roses themselves that are defective??? I'd rather not waste the money purchasing new roses, but if there is no hope for the current roses, I may have no choice.
I plan on getting both a soil test and a pH test on that soil in which the roses are planted.
Any other thoughts you have are appreciated. Thank you so much for your time.

It sounds as if you are doing all the right things, and the environment looks perfectly suitable. There doesn't appear to be anything else that you should be doing, especially if the previous roses grew well and didn't have any issues. The only two considerations might be: 1) dog urination on these plants or 2) if there was concrete spillage or some other type of chemical/salt/oil that leached into the soil during the re-landscaping.

My suggestion is to get the soil test. When you get the results, you can contact the Arapahoe County Extension Office, as they receive a copy of your soil test. The Horticulture Staff is there to help you understand the results and suggest the appropriate course of action. Again, pH levels and levels of Phosphorus and Potassium are important for roses.

If the results are normal, wait until the spring growth and bloom flush (about June). If they still appear to be sickly, then all indications may point to defective plants. I would consider this a really uncommon occurrence for (what looks like) four roses to all be defective.

Finally, the only other recommendation is to contact a Master Rosarian from the Denver Rose Society. This is a great organization that purposes to educate on all things roses.