How to prevent rose replant disease or what causes soil sickness in rose beds are two common questions, although the problem doesn’t just apply to roses. It can apply to many species and fruit trees in particular.
Some rootstocks seem to be more resistant than others but it is a fact that for some plants, including roses, there is a strong possibility that when a plant is replaced the replacement does not fare well. Why?
If the original were dead or dying it might be fair to assume that if some form of disease had stricken it the disease would still be present in the soil and ready to attack.
However, even when apparently healthy specimens are removed, there is a strong possibility that the replacement will not fare too well.
There are a number of theories regarding the reasons and causes, some more credible than others.
One strong possibility is that as a rose (or a complete bed of roses) becomes established it becomes colonised with various micro organisms: some ‘good guys’ and some ‘bad guys’. Most, in fact a very large majority, will be the good guys with just a few baddies skulking around and looking out for any opportunities they can. A bit like many animal populations in fact (including humans!)
The point is the bad guys aren’t around simply to attack and destroy your plants, they need ‘food’ and if all the ‘food’ has been consumed by the good guys, there is nothing left for them. Take beneficial fungi – mycorrhizae – these ‘feed’ on excess carbohydrates excreted from the plants’ roots, leaving nothing for the non-beneficial, pathogenic species.
If you remove a rose, or any other plant from the soil, you are likely to destroy much of the mycorrhizae. When the new plant goes in the pathogens and other bad guys will be waiting.
There are a number of things you can do to prevent or at least reduce the likelihood of the problem:-
a) Replace the old soil with new. An old gardeners’ trick is to dig out a hole and place a cardboard box big enough to take the new roots or rootball in the hole and plant in the box with new soil. The cardboard will provide a barrier until it is decomposed, by which time the plant should be well established.
b) Ensure that a colony of beneficial fungi is established by applying mycorrhizal fungi.
A product like TNC MycorrMax for example contains mycorrhizae and beneficial bacteria with added natural products to stimulate their growth. Tests have shown that mycorrhizae can make a dramatic difference to root growth1 but it is important that the soil should be rich in organic matter and chemical fertilisers and pesticides should not be used.
TNC TricorrP5 contains other species of fungi – trichoderma which which are antagonistic towards pathogenic fungi and have been shown to be beneficial in the control of harmful nematodes
c) There is evidence that vermicompost can suppress nematodes2 and other undesirables3. So if you have a supply of vermicompost, it might be worth adding this to the replacement soil.
Original article written by Bryan Davenport - August 20, 2013
2. Arencon et al, 2003
3. Arencon et al, 2007