Hi folks,
Complete beginner here, getting frustrated with trying to grow something that should grow like a weed!
My seeds (Royal Queen Seeds automatics) all germinate well (damp tissue method), and when their taproots are 1-2 cm long I plant them out in small pots, approx 0.5-1 cm deep. Compost is mgc24 “bio-hanf” peat-free brand. They grow, possibly a bit stringy, but maintain a nice green colour, on the windowsill. When they have another couple of pairs of leaves, after their cotyledons, I move them outside, to a SW facing patio with a wall behind them. It’s been warm, but rarely >30 C, and I’d say it’s been sunny enough - the rest of the garden is fine….
Then the plants stall - they get a few more leaves, never show any interest in e.g. the stalk branching, and turn a uniform paler green. They do not grow taller than approx. 10 cm, with my oldest plant from late May having started to grow a single tiny bud (is bonsai cannabis valuable :-) ).
The water here (Berlin) is quite hard, but still tests as having a pH of ~7. I’ve also tried watering with rain water and acidified (citric acid - it’s what’s in the Biobizz pH down) water.
I’ve tried Root Juice, Fish Mix and Alg-a-mic fertilisers from Biobizz, nothing seems to make any difference, and with such small plants it’s difficult to not overwater. I’d also expect the compost itself to still be providing enough nutrition for such young plants?
All help/suggestions gratefully received - thanks! Sorry for lack of a picture - for some reason it’s not letting me upload anything.
That is severe nitrogen (N) deficiency.
Three ways this happens:
Not enough N added in fertilizer/compost etc.
Organic matter with high Carbon:Nitrogen ratio locking up the N as it decomposes. In order for bacteria/fungi to break down plant material they need a C:N ratio of 30:1. Wood chips are 250-500:1.
Over-watering. Bacteria convert all types of nitrogen in aerobic conditions to NO2- and then NO3-. Both NO2- and NO3- are highly water soluable and leach out of the pot quickly. In severely waterlogged soils anaerobic conditions occur. This triggers bacteria to convert NO3- to N2 gas and it returns to the atmosphere.
Thank you also for the very detailed reply - from those options I think 1) and 2) are unlikely in my case - it’s a pre-fertilised compost designed for cannabis and should still have enough nutrients (plus during various stages of panicking I added N-Rich fertiliser (Fish mix) and no change occurred). This leaves 3, which has been the suggestion of others as well - although from your explanation I’ll be careful about reusing compost and will use new compost and add further fertiliser if required.