Polystyrene Propapacks

At least I think thats what they used to be called! Does anyone know where you can buy these from now? I'm sure I bought them from Marshalls a few years ago but they aren't on their website :confused:

 

Hi helen

Is this what you are looking for?

still available from two wests and elliots

http://www.twowests.co.uk/TwoWestsSite/pages/product/product.asp?prod=PTIC&cookie%5Ftest=1

 

Do they work? and are they any better than a ordinary covered seed tray?

I bought two small ones recently, because they were being sold off very cheap, at a closing down sale. But I have not used them yet.

 

I think its the polystyrene thats sort of a good insulation against variations in temperature (it even feels warm to the touch)but they are probably disappearing due to polystyrene not being an eco friendly product, although for some purposes it can be crumbled and added to compost

I have 2 standards outside the door, 1 bay 1 olive and I have these stood on sheets of polystyrene which is excellent in stopping the cold transferring from the concrete to the pot

 

I believe that polystyrene, as Steve says is a good insulator against variations in temperature, but surely early on in the season you want the pots to warm up quickly.
Have you ever moved your pots Steve during frosty spells? I'm willing to bet that under the pot its not frozen.
The cold comes from above, thats why you cover the ground and plants to stop ground frost in spring.
If we lived in the tundra and had permafrost then I believe it would make sense to raise pots off the ground, but I cant see how it works in the UK.
Just one of my crazy ideas, I dont suppose anyone else sees it that way?
:D :D

 

Steve, you may be right about these growing trays disappearing, but in the wider context there is more expanded polystyrene about than ever before. It is the ideal packing for computers and electrical equiptment as it is so light and strong.

It is now being used widely in the greengrocer trade. Those boxes are excellent for storing Dahlias etc over winter. because they are such good insulators. You can even fill them with compost and grow veg or whatever in them. I am told that greengrocers are only too pleased to give them away. Not bad for a freebie!

 

There is an amount of cold comes through the floor, I have worked in a factory where people at benches have had duck boards to stand on or rubber mats...it wouldn't be frozen under a pot because the pot is covering the floor but I think it would still transfer the cold into the ceramic pot

I have stood on concrete floors in winter and stood on polystyrene...I know which I prefer :D

 

Yep, I see where your coming from Steve, but were these places heated at all?
If so it would be definately warmer off the floor.
Why do water mains not freeze? Its because the pipe is below the depth that frost is likely to reach. Therefore the frost comes from above.

 

Slightly off topic but cold doesn`t move, heat does

Personally i can`t see the benefit of an insulated pot if it has an uninsulated surface
ie: the the soil surface, which will lose all the heat albeit a bit slower than an uninsulated pot.

How warm would your house be if you removed all your loft insulation

 

Good point Hex, Although I think I am guilty of hijacking Helens thread here.Should I start another one?

 

Ok, I agree to differ

But if the water mains were laid along the ground would they freeze? the 2 pots in question aren't buried under ground but standing on the surface,

I have Cannas and Callas buried underground which I hope are going to come up

 

The fact that the ones in the ground might survive better than the ones in a pot proves as far as I'm concerned the point, the ground is warmer than the air.
Have you seen how snow melts quicker on concrete than on grass unless the ground is already frozen.The snow on the grass is not in direct contact with the ground, so lasts longer.

 

Polystyrene is a very good insulator, but I suspect that was never the reason it was used in the Propaks. The main reason is that it is cheap, light and strong, and easy to mould into any shape. The insulation effect I think is irrelevent.

As far as standing pots on polystyrene, I think the effect is to insulate the pot from the ground (ie cut it off thermally). The pot by itself has a lower thermal mass and will heat up quicker during the day when the air temperature is higher than the ground temperature, but will cool quicker at night when the air temperature drops below the ground temperature. Without the insulation it is thermally joined to the ground and heats up slower during the day, but cools slower during the night. When the air is very cold, the ground is usually warmer, so the pot will benefit by being thermally joined to the ground.

Incidentally if you live in the furthest north of Russia, in houses built on permafrost - no one has mains water. The pipes would be frozen solid. Water is delivered everyday - hot! I bet their greenhouses take some heating.

 

Concrete will heat up much faster than earth due to it`s smaller mass (even 50 tons is small),hence snow melts faster.

The earth in comparison has a huge mass (thousands of tons all thermally linked)and warms much slower which is why snow doesn`t melt.

The temperature at 12ft deep is almost constant all year round.
Heatloss is governed mainly by temperature difference, surface area and insulation value so a pot standing on the ground wouldn`t see much benefit from being thermally linked by the bottom of it.

 

Got it in one peterS