On 26/07/16 11:30, David wrote:
Following on from previous observations about growing Buddleia in pots,
and lack of water.

This year (spring/summer) we had a prolonged period of rain, and the pots
seemed to flourish. I took this as a hint that in previous years they
hadn't had enough water.

Using the Buddleia as a guide to when to water, I have been giving a lot
more water to my other pots. They all seem to be having a bumper year
instead of just surviving. I am having to water in general at least once
per day if it doesn't rain.

This has also made me wonder about the Bougainvillea and lemon trees which
over-winter in the shade of the veranda. For the last couple of years they
have looked healthy all through the winter, but dropped their leaves in
spring and taken until early summer to get going properly. I am wondering
if I am being too cautious about watering them once the days become longer
and warmer.

Finally, just to restate my theory of "indicator weeds".

If you have a few weeds (free and easy to come by) or if you prefer, small
plants in your large pots they will react far more swiftly than the
established tree or shrub to lack of food or lack of water.

If the weeds look pale, feed the pot. If they droop, water the pot.

Finally, if the weeds look disgustingly healthy but the tree or shrub does
not then investigate further.

Cheers


Dave R

Although I won't dispute anything you have written, here are some other
possibilities to consider.

If the pot has dried out, and the compost has shrunk (particularly if it
is soilless), then watering can have little effect as the water will
just run down the inside of the pot and not wet the compost
sufficiently. It is useful to observe how quickly the water exits the
pots after it is applied. It may help to add some washing-up liquid to
the water as that will help it to penetrate the compost. It can also
help to stand the pot in a large saucer.

A similar problem can occur if the pot is infested with ants, but the
usual giveaway is piles of dry soil around the edge of the pot!

As to "indicator" weeds, they would help if they have a similar or
greater need for water than the pot plant. Those with lower water
requirements may mislead as to whether or not the main plant needs water.

Then you have to consider root pests such as vine weevil. It never
ceases to amaze me that they never seem to go for weeds, but only your
most prized plants in pots!

In fact, watching the weeds rather than the plant itself may leave you
with a situation in which it may be too late to save the plant itself.

Exhaustion of nutrients is another consideration, especially for plants
which haven't been repotted for years. Maybe also consider build-up of
salts in pots which have been watered for years with hard water. All
these can have negative effects, particularly on those plants which do
not like calcium.

Just to be contrary, I've got one window-box style container used for
annual colour which persists in getting its drainage holes blocked in
winter and spring. I have frequently found it up to the top in water
after rainy weather!

--

Jeff