In the UK there is a company called ‘Living Soil’ who make amazing dry soil amendments.
Tap water in the UK contains calcium and other elements that can be good for weed. Outdoors you should be OK without messing around with this too much but if you notice discolouration on your plants it may be worth checking the ph of your water – Around 6 is good.
You can still start plants outdoors when it is not April. You could plant something in say August and all that would happen is that it would go straight into flower if there is enough darkness. In effect seeds planted when we have long nights (12 hours dark or more) will ‘autoflower’ and should be fine as long as they don’t get too cold. Less than 15 degrees seems to be when they will start to become unhappy. You can protect plants from the cold with cloches, cold frames, a greenhouse or by bringing them inside for cold nights.
You may also want to investigate using molasses – specifically black strap molasses. Some people only use molasses. You just put half a tablespoon into a small pot, add boiling water, let it dissolve a bit, stir in then add to your watering can or whatever. Added just before flowering begins this definitely ads to the weight of the buds.
‘J Arthur Bowers Multi-Purpose Compost with added John Innes‘ is a highly recommended compost. Perlite is often added to compost to help it hold moisture.
Another option is to soak a tablespoon of bat guano in 5 litres of hot (not boiling) water over night, mixing well, and using the next day. Feeding every couple of weeks is normally sufficient.
They even have specific amendments for autoflowering plants. If you are in the US or Canada there is an alternative called Gaia Green.
Failing that, November could be a month to tidy up your outdoor grow locations for the following year. You may want to dig in some manure ready for the following grow season
Frisian Dew. A solid, proven photoperiod feminised outdoor strain which grows well in UK conditions. She is usually ready to harvest in early October. Grows well as far north as Northern England. Can finish bloom further north in mild autumns. One of the preferred and most recommended strains for growing cannabis in UK.
For many growing cannabis, UK slugs and snails are a massive pest. Slug/snail pellets are often repeatedly applied around the plants in generous quantities to prevent your plants being decimated by them.
How many cannabis plants can i grow in UK?
What’s the best soil to grow cannabis in UK? If your local soil type is too poor (e.g. too sandy) then simply supplement it with supermarket soil and some grow additives – fish/blood/bone meal, rotted manure, worm castings, seaweed etc.
Those growing cannabis in the UK may also consider LST (low stress training) for tying down particularly tall plants. June is a good time to start, before the plants get too large to easily manipulate.
• Day length September 1st: 13.5 hours
• Average temperature: 11–18°C
What are the best cannabis seeds for the UK climate?
• Day length July 1st: 16.5 hours
• Average temperature: 13–22°C
• Day length December 1st: 8 hours
• Average temperature: 2-7ºC