Even the best made garden plans can change. As you observe how plants perform and mature, take up more space, or simply rethink your layout, moving things around is a natural part of gardening. For most plants, this is no issue at all. Many can be dug out and immediately adding something new in its place is perfectly fine. Roses, however, need a little extra consideration when it comes to being replaced successfully.
What Is It?
The challenge arises when a new rose is planted where a rose previously grew. Known as rose soil tiredness, rose replant disease or rose sickness, it causes the newly planted rose to be stunted in growth, produce fewer flowers, and struggle to establish. Below the soil, root growth is restricted and may even die back. It is worth knowing that this condition also occurs with other members of the Rosaceae family such as apples, raspberries, and stone fruit like peaches or apricots to name a few.
The images below illustrate the impact of rose soil tiredness. The rose on the left has been growing for two years in soil where roses where roses were consecutively grown without soil replacement. The rose on the right is the same variety grown just a few feet away, and while it has been in the ground longer, the size difference between the two is far greater than the time difference alone would explain.
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What Causes It?
Research into the precise causes of rose soil tiredness is still ongoing. It is understood to be caused by a few factors rather than one single cause. Roses use a lot of nutrients throughout their life, gradually depleting the soil for the next rose. These deficiencies make it difficult for a new rose to establish. Compacted soil from years of growth is also thought to contribute.
More significantly, however, it is believed to be caused by a build up of soil pests and pathogens. Additionally, when you dig up a rose, fine rootlets are left behind in the soil. These decomposing roots release chemicals that negatively impact the soil environment for future roses. The presence of rose roots and the decomposition process also seems to attract harmful bacteria, fungi and nematodes, causing an imbalance in the microbial community which is difficult for the root system of a young plant to overcome.
Much of the scientific research on replant disease has been carried out in commercial nurseries and orchards, where challenges can be managed at scale. Rose soil tiredness of course is present no matter the scale and true from nurseries to gardens - from public to private.
How To Combat It?
In commercial production, the most consistent results come from combining crop rotation with cover crops. Fields are rested from roses and planted with crops that add organic matter, improve soil structure and help rebuild the beneficial microbial communities in the soil. Some cover crops are chosen for a specific job: Tagetes erecta (African marigold), for example, is used to help suppress harmful nematodes. Other operations move production into greenhouses, where roses are grown in fresh potted soil and field soil problems are avoided altogether.
Gardens, whether public or private, work within different limits. Beds are fixed by the design, there is rarely a spare field to rest, and a cover crop would mean sacrificing planting space for a season or more. Nematode pressure may also be lower in many home gardens than in intensive commercial plantings, and it is rarely tested for. Marigolds can be worth a try, but the evidence for them comes largely from large-scale plantings, so treat them as a possible extra rather than a fix. The good news is that there are simpler ways to give a new rose a good start.
If you are planning to plant a rose where one grew in the last several years, the best practice is to dig out a generous amount of soil, at least 60cm (2 feet) wide and at least 30cm (1 foot) deep, replacing it with good quality soil. If you have clay soil, be sure to mix in some clay with your soil blend so the new rose roots can become accustomed to the conditions of your garden, taking the clay from an area of your garden where a rose was never grown. Keep in mind that the conditions creating rose soil tiredness can remain in the soil for a number of years. Dispose of the removed soil in an area of your garden where roses will not be planted in the near future.
If a bed can be left empty for a season, a cover crop or green manure is still an option, and gives you a small-scale version of what commercial growers do.
Being well informed, combined with regular feeding and the addition of soil enhancers, means your rose garden will have what it needs to allow your roses to flourish for many years to come.
