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What is rose replant disease?
Rose replant disease is probably the most common example of specific replant disease, which can affect several other trees in the rose family, including all the fruit trees commonly grown in the UK.
It occurs when you try to plant a new rose right in the same soil one was growing before.
The soil itself is referred to as “rose sick”.
Identifying Rose Replant Sickness
Rose sickness starts from the roots, and is not always totally obvious above ground.
The most obvious symptom is severe stunting, where the rose grows only about 50% as much as it should be; if you don’t know what to expect, this might not be obvious.
- Shoots will be thin, spindly, with short intervals between leaf nodes
- Leaves might be reasonably healthy looking, but sparse
When you dig up a rose with replant disease to wash and inspect the roots, they will not have grown much, and you should see that fine roots are rotted and black-brown, not healthy and dirty-white colour.
What Exactly Causes Rose Replant Disease?
Research into the exact pathogens causing the disease is ongoing, but the main one seems to be fungi in the Nectriaceae family, which includes Coral Spot fungus, probably assisted by some bad Streptomyces bacteria, and nematodes.
The nematodes are probably a significant factor in spreading the other pathogens, and it has been noted that replant disease is milder in heavy clay soils, which are less favourable to nematodes than lighter, rougher soil types.
There are no roses resistant to it: if there were, they would be leading our bestselling roses.
Is there a cure for roses with replant disease?
No, there is no topical cure for a rose that is already suffering from replant sickness.
By the time the condition is apparent, it’s too late.
You may as well throw away the sickly rose; even if you replant it again, it will struggle to establish.
Preventing Roses Replant Disease
If you don’t want to grow something else, prevention the problem is possible.
Rose farmers use tractor mounted soil fumigation machines to kill most fungi and bacteria before replanting, and scientists might use radiation to sterilise soil in the lab.
Those aren’t available in the garden, but you still have a few options.
Leave the Soil Fallow with Marigolds Method
Dig the soil over with well rotted organic matter, remove any old rose roots, and sow a cover crop of marigolds, specifically Tagetes patula ‘Nema Mix’, to kill nematodes for at least one growing season.
Then plant roses using the wine box method below.
Replace Soil Method
- Dig a planting hole considerably wider and deeper than the spread of the roots; put the rose in the hole to check the roots do not touch the sides.
- Replace with soil from another part of the garden, or a fresh bag of John Innes No 3.
- Before backfilling around the rose, use a scoopful of Rootgrow granules and ensure that it is in full contact with the roots.
- Backfill, then mulch with compost or well-rotted manure for immediate nutrients.
- Water well straight away, and then during the first spring and summer.
- Mulch with well-rotted compost every Spring.
Establish Bareroot Roses in Pots with Rootgrow Method
If you plant a bareroot rose into rose sick soil and add Rootgrow at planting time, it’s not likely to help: the bad, parasitic fungi in the soil will have time to establish before the good, mycorrhizal Rootgrow fungi can protect the plants.
But if you pot up your bareroot rose with Rootgrow for one growing season, the Rootgrow will establish nicely, and you can plant it out with minimal disturbance in Autumn.
Wine Box Planting Method
Rather than going to the trouble of potting up your rose while the Rootgrow establishes, you can use a box directly down in the planting hole as a temporary “pot”.
Fill the box with fresh soil, add Rootgrow, and the cardboard should keep out the bad soil fungi long enough for the Rootgrow to establish.