Outdoor South East England grow timing question

Now I'm more worried about the current cold weather.... I've got a heat mat that is going to be attached to a thermostat with probe going into the soil, but have been reading that using the heat mat might fry the roots... Was going to Set the thermostat to keep the base of the pots at 20c. I don't think the led kicks out much heat....
What pots are you growing in?

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16l fabric ones...
I've read that you want to shoot for 20-23 degree soil temps so I reckon sitting a 16l pot on a 20 degree heat source won't pose too much threat to the roots, especially in the early stages of a grow when roots are 25cm north of your mat.

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as others already mentioned, I think you're a bit too early.

I grow photo's outdoor(never grew auto's), and my personal rule of thumb is they can go out around end april/beginning of may at the earlist. I'm in the netherlands, so probably similar timing for you.
for plants like tomatoes that don't handle frost well I learned from my father the rule of thumb that after 15th of may chance on nightfrosts is minimal, so safe to plant frostsensitive crops.

my experience is that weed can easily survive some frost, but they just won't grow much if it's too cold. one year I tried out how early I could go. germed some seeds, and after germing immediatly planted outside, around end of march-beginning of april. the seedlings emerged and had no trouble surviving, but they pretty much didn't grow at first, then at the very end of april they started growing rapidly.
so any time before the end of april is useless, since they won't grow anyway so you don't get more/earlier harvest, but they stay in their most vulnerable, small seedlingstage for longer, so more risk to lose the plants.

also with some earlier photostrains you can get in trouble with revegging if you plant out too early, so with really early photostrains it's better to wait a little longer.
 
I'd agree with others, it's a bit early. I've grown outdoor auto's both very successfully and disastrously in the UK, tho further north I'd say here is relatively low risk of late frosts, but they do occur. A one off frost might have little effect but several days of below 10C and the plants may well stop growing for a couple of weeks.

Mid April I'd start under LED (LEDs seem to produce less stretchy plants IMO), here they'd spend the first three weeks (veg stage) on a 24/0 cycle.

May is the month I'd be moving girls from their indoor start to a cold frame (a mini-greenhouse that is open to the elements during the day and closed at night). Here they'd spend another 2 weeks (by now flowering should be just starting). Then they'de be carefully transplanted (it can be done carefully without damage with a bit of ingenuity with a pre-cut double pot to start with).

Here we differ as I'd be transplanting into the soil - while you are staying in pots and don't need to transplant. In pots the only thing to be aware of in the early days is recognising air frost v ground frost. Air frost is a just that a cold bit of air one random night. Cannabis will generally shrug this off as long as the soil temperature doesn't drop too much. A ground frost is where temps remain cold over a period of time and in this situation you can expect an exposed pot to freeze if temps drop to zero one night. This will seriously stunt your plants if not make you rip them out and start again.

Of course in pots you can move them back indoors if it's cold - or give them fleece blankets to keep em warm - but if it's a guerrilla grow then perhaps digging them holes and dropping in the pots would be less conspicuous.

Good luck tho :D and let us know how you get on.
 
Right, well this will have to be an experiment then.... I took the first few bits of positive advice and germinated them last week. Have just poked through... If I put them on a 12/12 schedule for a few weeks would that slow them down? Maybe allow me to wait a bit before putting them outside (odour is limiting factor with keeping them indoors)? I read that flowering will start when roots run out of space, so if given less light would the roots grow slower?

This may all be academic if I can't keep them warm enough before end of march!

Thanks for all the advice
 
So they stayed inside, and surprisingly doing v well in a very cold place with a 60w ceramic bar heater. Prob a few weeks left... This march and April was too miserable for even my geraniums!
 
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