On 19 Apr 2004 13:04:29 -0700, (Zymurgy)
wrote:

Anyone know of any decent online references ?

If you search on

growing basil

you will find many.

I have several mature basil plants, but they have gone into flower.
Is this good ? I am trying to maximise crop and longevity.

Good for producing more seed; not good for maximizing crop. Pinch off
the tips of branches the minute they look as if they're thinking about
flowering. Snipping the flower stem and about 2 pair of leaves below
*may* help. Harvest by pruning stems just above a leaf bud rather than
just picking off a few leaves. Unless all you need is a very few
leaves. This will encourage branching and more leaves, which is what
you want.

Once cropped, will they regrow or should I replant more from seed ?

They *will* regrow. You can prune 1/3rd of the plant with no damage.
Basil, as others have pointed out, enjoys heat, light, and humidity.
It is *extremely* frost-tender and usually grown as an annual in
temperate climates.

I also have a mature Bayleaf (shrub !) and some large Rosemary plants.

Should these be cut back or left to grow to maximise crop ?

I'm not familiar with growing simply as an herb source. I thought you
just picked a leaf off a mature tree/bush. Googling reveals that
snipping the branch tips will make bay branch, also.

I don't know of any advantage of cutting back rosemary. A mature plant
has plenty of leaves/stems for culinary use. Rosemary *is*
Mediterranean and likes sun and that familiar "well-drained soil." Do
not over-water. It is a perennial and hardy to around -12C.