Edible Bulbs - Allium

Rodger Whitlock totototo@telus.net
Sat, 05 Nov 2011 17:25:34 PDT
On 5 Nov 2011, at 9:51, Richard Haard wrote:

> I would like to learn more about crop rotation protocols, what crops follow
> and how many years between bulb crops. In a garden situation, or a small
> field how much 'space ' is needed separating crops, or are there trap crops
> to use as cover cropping for nematode, virus and root rot diseases.

Jan de Graff, a one-time large scale breeder and grower of lilies in Oregon 
cooperated in the writing of one of those 'complete' books of this, that, and 
the other by F. F. Rockwell. In "The complete book of lilies; how to select, 
plant, care for, exhibit, and propagate lilies of all types" (Doubleday, 1961), 
de Graaf's methods are described in some detail. His practice was to lease land 
that had never before grown lilies, and then grow a crop on them, for one year 
only. Next year, completely fresh ground.

Many ornamentals, if the same genus is repeatedly planted in the same soil, 
begin to fail, presumably because of some buildup of disease organisms in the 
soil. Roses and primulas are among the genera affected. If you uproot all the 
bushes in an old garden of roses, and then re-plant, the new bushes will not 
thrive. The problem can be cured by inserting layers of straw into the soil for 
a season. My guess (n.b. "guess"!) is that the organisms that decompose the 
straw secrete substances injurious to the rose disease organisms.

The famous nut walk at Sissinghurst Castle in England, where hazels are 
underplanted with a carpet of primulas, gives the gardeners endless grief 
because the soil is now "primula sick", yet primulas must be replanted fairly 

These comments may help you get your head around some of the issues.
Rodger Whitlock
Victoria, British Columbia, Canada

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