When do you transfer tender stuff to your unheated greenhouse.

[Bohobumble]

I have a couple of polystyrene boxes about 18 inch square and a foot deep. When i take the tom plants down the greenhouse i stand the pots in these. For the first week or so cover them at night and take the covers off by day. If we get a mild spell i leave them uncovered and only cover when a hard frost is forcast.

Oooh OH had a shock absorber delivered in one of those polystyrene boxes... I was wondering what I could use it for!

[Lamboluke]

How much do the 450+ watt heaters that are for sale on eBay cost to run? Most show temp control between -3 and 30. So to have it set to avoid frost temps would be great for my currently unheated greenhouse.

This also might sound daft but how do I know if my greenhouse contents have been 'frosted' as it were. I know external frost is obvious due to the hard ground and visible frost, but my new roses which are currently being protected from high winds (newly potted too) have never had hardened soil suggesting they have been effected by frost despite having frost outside on a number of occasions. Is this because it's not been cold enough for long enough to get the temps down to frost levels inside? It's currently 0c outside but 5c in the greenhouse.

[Bigmallly]

Oooh OH had a shock absorber delivered in one of those polystyrene boxes... I was wondering what I could use it for!

I use that type of box for storing potatoes in sawdust for planting the following year..............sorry for tangentising............as you were.............

[Bohobumble]

I use that type of box for storing potatoes in sawdust for planting the following year..............sorry for tangentising............as you were.............

Oooh, good call!

[emzgogo]

Someone suggested to me few church candles each in a large jar enough air to stay alight and will produce enough heat to keep greenhouse above freezing. I may give it ago this yr for alittle fun x

[Jay-ell]

I'm surprised nobody has suggested a GH in a GH...........a blowaway or coldfame inside a greenhouse insulated with bubblewrap if need be.

I only have a blow away green house but I've a couple of wilkos 4 shelf mini green houses I'm going to put inside. May put one in soon with a mini-max thermometer to see how effective it is. Milk jugs full of water on the bottom shelf should help to keep it steady and absorb heat in the day to release at night.

[Kristen]

How much do the 450+ watt heaters that are for sale on eBay cost to run?

The other question is whether a 450W heater is enough to maintain the heat that you need, particularly on a cold night. A 450W heater on all the time will use the same electricity as a 2kW heater on a thermostat that only needs to come on 25% of the time ... but the 2kW heater will be capable of maintaining the temperature on much colder nights.

1kW running for one hour uses one unit of electricity. Haven't looked recently at what that costs, around 17p?

So a 450W heater, on continuously for an hour, would use (450 / 1000) x £0.17 = 7.65p

Biggest issue, IME, with heaters is that the cheap thermostats that come with them are useless, and the greenhouse might easy overrun the set temperature by anything up to 10C (expensive) ... or underrun it by 10C (dead plants ). An accurate thermostat, into which you can plug a cheap heater (with thermostat turned up to MAX so it relies on the external thermostat) cost £50, but may well save you that in one or two seasons.

No such accurate thermostats, that I know of??, for Bottle Gas or Paraffin heaters.

Someone suggested to me few church candles each in a large jar enough air to stay alight and will produce enough heat to keep greenhouse above freezing. I may give it ago this yr for alittle fun x

Sadly if it was that easy we'd all be doing it. Best bet to reduce fuel costs is to insulate the greenhouse, e.g. Bubble wrap, and reduce the volume you have to heat e.g. by having a room-within-a-room - a blowaway or small tunnel inside a greenhouse / conservatory. Or grow under grow lamps indoors or in an insulated "box" in a garage - i.e. provide the Light instead of the Heat.

Milk jugs full of water on the bottom shelf should help to keep it steady and absorb heat in the day to release at night.

Not enough sun energy, in winter, to warm the water enough to heat the greenhouse overnight. Adding thermal mass to the greenhouse will help (conservatory / lean to greenhouse against a wall perform very well), but its not enough to avoid the need for a heater on cold nights. If the milk jugs freeze it is unlikely that there will be enough heat the following day to unfreeze them, let alone capture useful sun energy.

[Bacchus]

It can be surprising how cold it gets undercover. On Sunday I picked up my water bottle with holes in the top to water some lettuce in the polytunnel and it was frozen - apparently minus 5 in there according to the min max therm..

I have a "very" raised bed in the poly tunnel (about 2' high) with plastic hoops over which I can put fleece. I'm thinking if I can find a good way to warm that cheaply that would be my first option when moving seedlings out.

[Jonnyt]

My Greenhouse hasn't been below zero this Winter to date despite today for example having ice on the roof panes

[Alison]

Personally I'd not put anything tender in my greenhouse until April at the earliest and then still be looking to bring it back overnight on a regular basis. I find it's much better to sow a little bit later when there is more light and less risk of heavy frosts but then again I'm too tight / lazy to sort out complicated heating systems.

[Thelma Sanders]

My Greenhouse hasn't been below zero this Winter to date despite today for example having ice on the roof panes

It doesn't have to be that cold to kill most of the veg we grow in there eg tomatoes, cucumbers, peppers etc. If they get below about 10 then they don't often recover.

On the other hand- in a cold winter the Sugarloaf chicory, I often grow, can have a frozen heart - but it recovers as it thaws out in any sunshine

So it depends what you're putting in there.

[TrysHard]

That will be me next year if I get bit by a frost, I will keep stuff indoors as late as I can and sow a 2nd batch of Chilies etc in late Feb just in case.

You can't have too many plants can you.

[Philthy]

Anything established i.e. pruned from a previous season, early april.
New sowings go on the bench May onwards - in trays with propogator lids (unheated, just the trays).
The greenhouse windows stay closed (bar a small crack for ventilation) until end of May.
I don't personally bother ferrying stuff between the house and GH on a daily basis. I pay attention to the weather forecasts and recent temperatures. But otherwise, once the plants are in, they're in for good.
Of course nothing is set in stone, and if there is an early and unseasonably warm spring, or winter refuses to back off, transfer times will be adjusted accordingly.

[Valleyman]

I'm in Kent and the last night below 5C tends to fall in the third week in April. And only for a few hours at a time.

I try and resist keeping tender stuff out of the unheated greenhouse until then, but usually get over eager and swamped by seedlings in the kitchen by the first/second week in April so always risk a few things out there at around that time.

Bear in mind that my greenhouse is... lets say "well ventilated", so if you have a nice fancy air tight one you may be fine at the end of march where I am.

[TrysHard]

Valleyman

I not far from you, so I note your advice, I know folk nearer the south coast in sheltered spots plant tender stuff direct in unheated greenhouse from Mar onwards.