Any advice on how I can encourage more growth?

hi i would say not enough sun,maybe?

Big pots don't stunt growth, small pots do. What do people think when plants in natutre grow directly in the ground?.......fastest growth possible! Outdoors is all about how much DIRECT sunlight reaches the leaves. Are they getting full, direct sun all day or only a few hours? Find the sunniest spot possible and if you are taking them inside at night, are you getting up before dawn to make sure they are outside in the sun for the whole day or are you sleeping in and only putting them outside mid morning? You may be better off just leaving them outside. Fill those holes in too, they are not helping anything.

Don't mess with it too much. The plant will do what your substrate and watering/fertilization habits provide. in future make your substrate fluffier with more perlite or similar amendment. in high water capacity (soil / sphagnum peat moss) you want 1:1 (50%). in something like coco you only need 2:1 (33%). Better roots = better growth. anyone telling you to only water a portion of the pot is not helping you. When you irrigate you always make sure the entire thing gets wet. If constituted properly, "overwatering" from this simple act is impossible. Wait for top 1" to dry. Repeat. Anything that varies from this too much is only going to cause problems. The wet-dry cycle ensures a couple things. First, it's always moister deeper into pot, so roots grow toward moisture -- it is not a thought or fefeling of the plant. it is physically built into how roots grow. The greater level of moisture in any particular direction will cause it to go that way. When you water superficially or incmpletely, you get more superficial roots, which if uncovered at all and exposed to light differentiate into useless stems in short order. Not watering the entire thing also causes dry pockets, which if they repeat and you get that same ebb and flow of moisture evaporating around edges, you will get nutrient buildup in those zones over time. Keep it simple. Water. let it dry. Repeat. feel the weight of the pot, you can more easily tell when it is ready for irrigation. don't dig holes in future or put skewers into it unelss there's some extreme context that warrants it.. just going to tear up roots and damage the plant with minimum impact from it. This is young so not a bunch of roots.. no harm; no foul. Less is more... what we do should be minimal. let the plant do the work. constitute your substrate better... things shouldjust happen on their own with little input from us. It's not that bad for day 16. It's outdoors and early in your growing season, maybe a bit cold at night? these are not optimal growing conditions. If you haven't begun fertilization, you could probably start with 1/4 stregth for soil nutes, but i think this is a matter of how strong the sun is at the moment as much as anything else.

Make sure there is a gentle breeze hitting g the canopy at all times, that 2"3 lip will prevent alot of air passing under the leaves at a time it needs it. 0.04% of air is co2. The plant is roughly half the size underneath as it is above. If it's 3" tall the roots only penetrate a couple inches too. Gravity will pull the water to bottom of a big plastic/ceramic pot, this normally pulls it out of reach of the roots of the tiny plant. Ideally we water away from the plant so the roots will go looking for water, but until the rootzone is established it can seem like things get a little slow as most of the water sits put of reach for first week or so if germinated in such a large pot.

You'll get better results with drainage adding the holes to the bottom of your pots than digging little holes in the surface. A looser soil would help even more. Perlite is a great product that helps promote healthy roots through drainage and aeration.

Easy buddy another uk grower here :) I have grew outdoors too and find it very challenging. there is a guy called the outdoor warrior on youtube who has pretty much perfected gorilla growing in the UK. he was even on tv about growing weed on other peoples land lol your main problem is light buddy. the UK has great light and conditions for growing cannabis that's why there are so many huge industrial cannabis farms dotted all around the UK. not common knowledge but the UK is one of the largest exporters of cannabis even though it is still classed as a class b controlled drug. how do they do it ? its all about the conditions and placement of your pots south facing gardens often have the most sunlight hours of the day so smack out a compass on your phone and see if you can find a space that is more south. you want to avoid the shad like a plague as cannabis needs all the light it can get. i would advise looking for large things around your pots that could be casting shadows on your plants in certain hours when the sun is at certain points in the sky they don't look overwater to me infact they look like they need a little bit as that medium is quite dry I'm not sure why you have holes in the soil too is this to help air get to the root system ? if so you would be better of waiting until these plants are larger and then transplanting them into airpots :) anyway with all that mentioned I wish you the best of luck in your outdoor cultivation keeping the UK green one plant at a time :)