Iain,
In the interest of linguistic accuracy, may I point out that you have unwittingly repeated a common error - to descibe proprietary substances that can be applied to plants simply as "chemicals".
On reflection you would probably agree that "chemicals" also embraces alomost all substances. We ourselves, and plants, (even our Macs) are composed of chemicals.
No offence intended.
My interest lies in trying to reduce the misnomers perpetuated in, among others, the popular pres. In such publications, accompanying an article about air pollution, you sometimes see a picture of an electricity generating plant's cooling tower as if this were a pollution source. In fact those emissions are merely harmless water vapour. Even the Financial Times has committed tis error.
IMHO, in these days of information overload - and too many people in the media wanting to plant false, or unproven, ideas into our minds, it is important to try to use words correctly.
A sceptic wishes you well.
ejc