On Sep 18, 4:42 am, michael > wrote:
> I thought that I would try again to further my understanding of
> observations on my vines in England this year,based on the very useful
> replies and discussion.There will always be disagreement,but as
> someone new to growing grapevines,I hope that I can understand the
> issues.I apologise to doubi..for my recent comment,and hope that he
> can continue to help.
> Let me try again to summarise my recently gained knowledge:
> 1)Using wood chip as a mulch on the surface around the vine can
> greatly help in the stabilisation of upper soil moisture content,and
> will not affect the nitrogen of the vines-rotovating or digging in
> wood chip will rob the soil,and this is my gardening experience.Garden
> compost could be even better,as it introduces a living worm population
> which may help soil texture.
> 2)Wasps or other insects are not the source of primary damage to
> ripening grapes,but can spread the rot to other grapes in the bunch.A
> primary source of damage could be a heavy rain shower,causing
> splitting,followed by wasps,etc moving in.I think that this is what
> happens with plums after they split when nearing ripeness.My culling
> of the majority of the wasp population will still help,I believe.
> 3)I thought that darker vine leaves to be an indicator of too much
> nitrogen.I would like to know what the indicators are for vines
> needing more phosphates,or potash,so that I know what fertiliser to
> add to my compost.
> 4)One indisputable fact is that my vines and grapes are sofar much
> healthier this year. I believe that probably the main cause is the
> long very warm dry spell here in June-but I do not really know.It
> could be the compost keeping moisture levels stable.
> 5)My original post was about pruning of laterals or sideshoots for
> vigorous vines in a cool climate.My policy now is to remove most of
> them in June and July to prevent a dense canopy developing,thus
> encouraging powdery mildew,and then leave them alone after veraison to
> have maximum leaf for the ripening period.
>
> I hope that my understanding is improving and welcome your comments
>
> Michael

The following link provides pictures of grape leaves with various
nutrient deficiencies. Potash (potassium) and magnesium are the most
common. Magnesium can be easily supplied with a few spoonfuls of
Epsom salts. I read the other day that grapes usually don't need
added phosphates. http://www.honeycreek.us/leaf_chart.php

You hit the nail on the head about the benefit of mulch. If you had a
long warm, dry spell and your vines remained healthy, it was due to
the stable moisture levels enabled by your mulch.

Stephen