by Nanette Londeree, Master Rosarian
As winter approaches and you begin to plan for adding new roses, you may be in the situation that you’ve run out of room, but just “have to have” a new rose. So you go through the process of elimination and decide to remove a rose or two and pass it along to a friend. You get your new rose, plant it carefully in the recently vacated space, and all seems well, for awhile anyway. Then you notice that the rose just sits – it doesn’t show any significant signs of growth – though it also shows no sign of pests or disease. It just sulks. Growth is may be stunted and bloom production slow regardless of how well you care for the rose or how often you fertilize. This may go on for a season or two, until either you just loose patience and yank it out, or it finally takes off. There could be different causes for this apparent behavior and one is something called “soil sickness” or “rose replant disease.”
Neither of these terms are really appropriate because, from a scientific perspective, a disease or sickness is the result of an infection of a pathogen or causative agent, and for this malady, none has been identified to date. Nevertheless, there are plenty of rosarians that have experienced this malady. Like many things in the rose world, there is general controversy whether there is a disease at all, and if so, what the causes are. Theories range from allelopathy, microorganic deficiencies, mineral deficiencies, fungal build up in the soil, nematodes and autotoxicity. By the way, this phenomenon is not isolated to roses; it has been observed in other susceptible plants such as apples, pears, plums and cherries, when new trees are planted in soil previously occupied by members of the same genus.
Allelopathy is a complex phenomenon which Pliny the Elder, a Roman natural science author, first wrote about in 77 A.D. In his writings he noted the toxic effects of black walnut on neighboring plants in the landscape. Allelochemicals are metabolic by-products of certain plants that, when introduced into the environment, cause growth inhibition by affecting physiological processes such as respiration, cell division, and water and nutrient uptake. Symptoms of “allelopathic effects” include leaf wilting and yellowing, or death of part or all of a plant. In the case of the black walnut, most other types of plants have trouble growing under or around the tree as a result of the production of jugulone from the roots. If the theory that roses produce some type of inhibiting chemical into the soil by their roots, it doesn’t explain why other plants have no problem growing in a space where a rose has previously resided. It would also seem that if this allelopathy were a true problem, adjacent roses might be impacted, but that does not appear to be the case.
Autotoxicity is the self-destruction of a species through the production of chemicals that escape into the environment and directly inhibit the growth of that species. Many plants manufacture toxins to battle off insects, animals and diseases. The plants have various ways of containing those toxins internally so that only the enemy, and not the plant itself, are affected. If those toxins are released, either into the soil or onto the leaves, self-damage can occur. However, if plant toxins are involved, why are they mostly ineffective against the rose’s myriad enemies, from insects to diseases to deer? Even roots are subject to invasion by fungi, bacteria and nematodes.
Another theory suggests that decaying rose roots give off some type of gas that is toxic to new rose roots. This doesn’t seem too plausible if roses are growing in a soil richly amended with organic material – why would the decaying roots would differ from any other decaying material.
Other suggested causes include nutrient or mineral deficiency, fungal build-up or nematodes, the small microscopic eel worms that may gradually build up in the soil and eat the roots of the rose bush. Another possibility is Armillaria, a soil fungus that attacks oak, yellow pine, willow, raspberries, stone fruits, nut trees, grapes, currants, gooseberries, strawberries, roses and other rosaceous plants.
As there is no definitive cause of this collection of symptoms, there is no “cure.” You can take some precautionary steps however, to ensure that you don’t have the experience. The easiest method is to remove the majority of the soil the rose was planted in and relocate it to another are in your garden where it should be perfectly suitable for growing plants other than roses. Since this malady doesn’t affect non-rose family plants and trees, moving the old soil to another location in the garden and relocating that soil back into the newly planted rose’s location is merely a matter of muscle power and a wheel barrow. Then add new, healthy, amended soil to your hole and plant your new rose.