Bulb Log 05/09/07

[ashley]

Ian,

First may I say thanks, not just for this Bulb Log but for the whole long series over (almost) half a decade.  They have taught and inspired me a lot, as I suspect they have so many other people.  Well done. 

This week I was particularly interested in your comment on the sand base beneath the array of square pots.  How deep is it, and can excess water drain away?

All the best, Ashley

[Ian Y]

Well thanks Ashley for your kind comments.
The sand varies in depth. In the bulb house and the frit house the sand is a good 7cms deep as it used to be the plunge beds for the clay pots - I just removed about half of the sand.
In the other house the sand is only about 1 or 2 cms deep as the pots sit on aluminium trays.
No matter what depth the sand is its main purpose is to act as a sump drawing out the surplus moisture from the pots and yes all the plunges and trays are well drained so the excess water escapes.
The deeper the sand - the bigger the volume- the less often I need to water the pots.
However I am very conscious of the fact that I was too cautious, having just moved over completely to plastic pots, that I did not water enough at the critical times last season this I will rectify.

[Lesley Cox]

There's quite a lot about this in the most recent update of the Wisley Alpine Log (click at top of this page) and I learned a lot about drainage in pots from it. Well worth a read.

[mark smyth]

Ian what size box are the Colchicums in?

[Maggi Young]

Popped outside to measure box of colchicums, Mark... lovely evening about 15 C and no breeze.
Box is 30 x 40 by 30 deep.. all cms.
I reply because it is long past Ian's bedtime, even if he were not off to East  Mid ? Anglia tomorrow to visit the AGS. He's giving Frit. and Erythronium talks, I think. He's looking forward to seeing Jane and Rod Leeds again, who are kind enough to be taking care of him.

[mark smyth]

Rod and Jane are great just like Ian and Maggi!

[ashley]

Thanks for clarifying that Ian.  Although the sand provides a moisture reservoir and avoids ‘perched watertable’ if there is contact with pot contents, presumably the thermal inertia of a deeper plunge also moderates temperature fluctuations.  Can you judge yet whether this latter is less important for bulb happiness, provided close-packed square pots shade one another?

[Maggi Young]

Ashley, I think we will need to work with the all plastic pots for another year or two before we can be sure of what the overall effects will be ... Ian will likely comment more when he gets back from England.

[ashley]

Thanks Maggi.  Yes it'll probably take at least a couple of seasons for that to become clear.

[bendgardener]

Ian, in a previous log I recall a comment about the plunge being heated.  Sounds like a great idea.  How much heat would a plunge need?  In the Central Oregon Cascades (Oregon, USA).  We have two seasons, winter and getting ready for winter. 

[Ian Y]

Ashley
The thermal mass point is a very good one and in an ideal world it would be better to plunge all pots to their rim a deep sand plunge - this would moderate temperature swings.
We will see how things go on but to date I have not observed and problems with the bulbs due to that factor perhaps because we live close to the sea and have a very moderate climate. Perhaps the very warm spell we had last April that caused many of the bulbs to shut down prematurely could have been reduced if they were plunged but I know many growers who still use plunged clay pots had exactly the same problem.
As for heating the plunge - I do have thermal cables running through the sand as a protection against freezing in the winter. These are controlled by thermostats set at zero degrees C and they do not come on very often most winters but if we do get a prolonged period of frost they will save a lot of bulbs from dying. This is even more important now that I am using plastic pots that are not plunged deeply in sand as they will be more susceptible to penetrating frost.
I could turn up the thermostats and heat the bulbs but this would make them flower too early when the light levels are dismal this far north.

This weeks log will not be appearing until at least the weekend as Mr Admin is other wise engaged this week.

[tonyg]

I switched from plunged clays to square plastic pots some years ago.  I have always raised seed in plastic pots stood on a 10-15cm deep bed of sand and noted that the seedling bulbs were thriving while I had mixed results in clay pots due to careless under watering.  I do think that each approach can be as successful as the other if you get the watering regime right. 

My plastic pots just sit on top of the sand, not plunged at all.  It is important to recognise that they do not initially have 'good' contact with the sand below.  After several waterings the pots settle and the compost in them compresses slightly, only then does the capillary flow between sand and pot begin.  I guess that I could assist by raking the sand surface, loosening it and then pushing the pots in gently.  Although as Ian suggests the sand acts as a sump, drawing excess moisture out of pots, it can also serve as a reservoir, helping to maintain 'background' moisture in the lower half of the pots (where root activity is greatest) both during the growing season and later.  Down south where I live dessiccation during the long hot summer (OK not this year can be a problem which I find is offset by the slightly damp sand beneath the pots.  Most of my pots are at ground level, in cold frames.  On benches in the greenhouse the issue of temperature fluctuations is far greater.  Although this is due in part from the glasshouse effect, the ground does indeed act as a thermal sink as Ashley suggests.

[ashley]

Thanks Ian and Tony.  I agree that placing pots on the ground or in a deep plunge is the ideal, though not always practical.  Presumably thermal fluctuation bothers some species more than others, so it comes down to trial and observation!

[Joakim B]

Maybe a stupid comment but potsize must also influsence the temperature swings with big pots beeng a bit slower in changing due to more mass compared with small pots. At the borders of the pot it might not be much difference but in the center there should be.

Just a simple thought
Joakim

[ashley]

True Joakim.  The problem is that some (most?) of us are greedy, wanting to grow as many different species as possible in a limited space!  Hence the minimal pot size.  As Kristl says, 'So many species ... so little time'