Keeping a greenhouse warm over night using hot water?

[maverick451]

Hi guys

Planning ahead I would like to get my Tomato plants in the greenhouse in Mid April before they take over the house.

If a cold night is forecast I had the idea of putting a water butt in the greenhouse and filling it with really hot water (I have a hot water tap outside so can just use a hosepipe)

Do you think may work?

[veggiechicken]

Let me think about that - No

[maverick451]

Thankyou very much for that post , truly enlightening

[veggiechicken]

How would the water stay hot?
Just thinking how quickly a bath of water cools down - it would be no different in a water butt. You couldn't insulate it to keep the heat in as you want to heat to come out.

[alldigging]

Nah that's a mad idea. Water won't stay hot for long.

[Guest]

However.........I have read some where having quantities of water (tanks/barrels etc) is meant to help raise the temp but only by a few degrees

[Alison]

Will only make a minor difference and won't stop a proper frost.

[Kristen]

The "problem" as I see it is that anything "tender", such as Tomatoes, Cues, Peppers, etc. need minimum 10C. Nothing Health Robinson is guaranteed to provide that, all that they will do is reduce the rate of cooling. It's fine in years when there are no late frosts, and no harsh frosts past February ... but in other years the risk is total failure of all seedlings. I suppose one could take the chance, and in those years re-buy as plants from the nearest Big Box Shed - but their plants don't come in many varieties, and choice of varieties is important to me.

Plan B (OK for Home, not so OK for Allotment) is to bring the plants in on cold nights. Its only for the night, so utility / kitchen floor would do. Yeah its a PITA, but its only for a few nights in the Spring and means a good crop of vegetables through the summer.

Not sowing too early is also import. Folk are often in a rush to "grow something", but better to delay until the plants can be looked after. Really early sowings, with mediocre late Winter sunlight, made worse by growing on a windowsill rather than greenhouse, or in relatively low temperatures in cool greenhouses, are only going to be a few days ahead of crops sown later ... to get a properly early crop needs a heated greenhouse, and probably extra light from growing lamps.

[Shadylane]

Tomatoes will cope with temps much lower than 10c though. They won't like it but they'll survive. Last couple of years I've had mine in the greenhouse around March I think and while they sat and sulked, once it warmed up they were fine. They also kept going well into late Autumn despite several frosts.

I used to bring them in at night and one year left a few out, as there wasn't room, they were spares and I couldn't be bothered. In the end there was no difference and they all seemed to catch up with each other.

[Kristen]

Tomatoes will cope with temps much lower than 10c though

Yes, that's true. The problem with sub-10C temperatures is that it changes the chemistry of the plant - leaves go Purple (I've forgotten what the chemistry is, failure to utilise Phosphate or something like that) - and it takes the plant a long time to revert to growing normally again, can be long after temperatures are back above 10C.

I suspect its a survival characteristic - Temperature=Cold, go into survival mode, don't come back out of it again until temperature has been "warm" for a decent length of time.

There is also the potential risk to the plant from being stressed - it might be more susceptible to whatever infections are going around and so on.

Several "IFs" in there, but IMHO much better to avoid temperatures below 10C (e.g. by sowing later, or providing heating) rather than sowing & growing such that the plants are bound to encounter low temperatures. Some/most years there is no problem, other years the crop may succumb as a consequence. I'm also sceptical that the start of cropping is advanced much by early sowing, and then keeping the plants on the cold side, compared to sowing later. I need to make an experiment this year keeping a couple of early sown tomato plants with minimal heat to see how much earlier they are compared to late-sown ones.

[Scarlet]

Is your greenhouse close to the house? Can you bring them in on a very cold evening? Wrap them in fleece during the nights where the temp isn't going to dip too much? Depends on how many plants you have really, but on occasions I've use those polystyrene fish boxes with lids for an overnight hotel when I've got a few tender plants that I want kept warm.

[arpoet]

If you have an solid fuel oven, put some house bricks in and before you go to bed take them into the greenhouse... Or... Have a dalek filled with hos muck in the greenhouse and take the lid off at night.

[Bill HH]

Get half a dozen tramps to kip in there.

[rary]

I heard an organic gardener saying that he used containers painted black and filled with water tied up into his trees to keep the frost off his apple blossom, and just using sunlight to heat it up. So if you try filling a container with hot water, put it near your plants and if possible cover the lot with fleece, I would advise that it can be sealed ie, a cap or lid, and remember, if you don`t try it you will never know.

[KevinM67]

Sorry, maybe not the most constructive post but - why the big rush to sow things so early ?

Edit to add - this post was not necessarily directed towards the original poster.