"Peter" wrote in message

Does anyone know if weed seeds can be killed when they are immersed in
water
for extended periods? If so, how long does it take?

Yep. As long as it takes them to start looked semi rotted. If they don't
start to rot (ie break down) then they can still germinate. If you add them
to a mix of manure in a drum and the lot starts to fester, then it shouldn't
take too long - perhpas a week in hot weather if the drum is in the sun, but
really it is probably weather dependant and weed dependant and 'fester rate
of drum contents' dependant.

I've just started using
my grey water to draw nutrients from my grass clippings (and clipping
compost) to avoid adding the clippings directly to my vege patch. I'm
trying
to reduce the amount of weeds that spring up whenever I turn my back.

Or should I just chuck the "spent" clippings into the greenwaste bin?

Don't do that as it's a waste of free nutrients. Those weeds will all be
taking something from your ground and if you notice what weeds come up each
year, you will notice that some weeds will appear one year but not the next.
Some weeds will also appear in certain situations and are a good indicator
of soil fertility/poverty etc. Sometimes the weeds won't reappear because
you've corrected a nutrient/mineral deficiency and the situation is no
longer condusive to those weeds. Sometimes they won't come back because the
weather isn't in their favour that year. I'd be very surprised if they
don't come back because you have no weed seeds left (but then you may be in
an area that has been intensively gardened and well maintained for decades
but I'm not in that situation so have an intimate relationship with my
weeds).

I do a number of things with my weeds. Sometimes I add them to the compost
(various sorts of systems running), sometimes I add them to the Black Jack
(liquid manure system you are asking about) sometimes I just drop them on
the ground where they were growing with the roots upwards in the sun. this
latter kills them quickly but I generally only do this if they haven't got
seed heads on them. The latter (pull and drop) technique is one that very
old gardeners often say results in the weed not returning. Dunno if that is
true or not but I have been told that it works because the weed grew there
because of the specific conditions that suited it and by letting it rot (rot
being a wonderful thing) where it grew than you are doing the same thing as
when one collects insect, runs them through a blender, strains the liquid
and then sprays it on the plants to stop the collected blended insect
attacking the plant.