Birch seedlings stopped growing?

[TheRollercoaster]

I planted these in sand early spring this year and they came out about 2 months ago.
What is concerning me is that they got to this state in about 2 weeks, then almost stopped growing at all.
Is there someone with some experience on birches that can tell me if it is normal for this species or am I doing something wrong?

 

[coltranem]

This my second year growing birch from seed. I have had similar instances where they slow down in the first year. The ones that have made it to the second year seem to be taking off better. I am not sure if it too much water or just a habit of the species.

 

[Leprous Garden]

To begin, I have no experience growing from seed.

BUT: why in sand? As I understand birches are not generally tolerant of dry soil. Maybe a wetter substrate would be better?

 

[Shibui]

Have you fertilized?
Sand has virtually no nutrients available to plants. Seed has a store to get emerging seedlings started but when that's been used growth has to stop until more nutrients are available.
Growth sometimes stops in hot weather but any birch seedlings that germinate here seem to grow most of the summer and end up around 1 metre tall by the end of summer.

BUT: why in sand? As I understand birches are not generally tolerant of dry soil. Maybe a wetter substrate would be better?

Fine sand like this actually holds quite a lot of water between the small particles. That sand is probably wetter than most bonsai mixes.

 

[Wires_Guy_wires]

Birch and birch like trees like stalling for a while, waiting out the summer heat and preserving themselves until the second half of summer.
The soil might also be too wet. Birches are tough in drains and rain gutters, on rooftops and other hostile places.. But we have to remember the ones we see come from buckets, and buckets of seeds that were dropped there over the years - if you ever cleaned gutters near a birch tree, a single specimen produces about a kilogram or two of seeds every year and they weigh about 20mg each. Those survivors are the proverbial 1 in 100000. When we grow from seed, we manage to get the other 99999 as well.

 

[TheRollercoaster]

Wow, i didn't expect so many replies, thank you very much to everyone. I'm going to address some of them.
SAND: i tried to grow seeds and cuttings of this same species last year in a standard organic mixture, had about 0 success rate, so i looked up online and saw some videos (can't remember the channel) where they suggest using sand for seeds and young pants, seems to be working for me. However they need to be kept in a closed environment, so the soil never gets dry, thus they now stay in a mini green house.
FERTILIZER: i didn't give them anything yet as i fear the young roots could get burnt or damaged someway. I have some biogold original, would you suggest using it?
TOO WET: I'll start watering them less frequently as the greenhouse they stay in is already contributing to retain a lot of moisture. I just thought young plants need the soil to never dry out as young roots could easily die for that.

 

[Shibui]

FERTILIZER: i didn't give them anything yet as i fear the young roots could get burnt or damaged someway. I have some biogold original, would you suggest using it?

I suspect this is the most likely cause. Definitely start giving them some nutrition. Biogold is an organic solid fert. It takes time to start releasing nutrients so great for longer term nutrition but not so great for immediate emergency nutrition. I would recommend a liquid fertilizer now for a quick boost and some biogold for longer term. Young roots being sensitive to fertilizer is a myth. All active root tips that do all the work are 'young'. Does not matter if the tree is a few weeks old or many years old. If the fertilizer is strong enough to harm seedling roots it would also harm older roots.
Watering properly is more tricky than many new growers realize. Plant roots need water but also need air in the soil. Too much water means not enough air and can kill. Not enough water can also kill but usually much more quickly so be careful not to get too dry. Birches are streamside species so tolerate wetter soils than many other plants. I would certainly err a little on the wet side rather than too dry.

 

[TheRollercoaster]

I don't have any experience with liquid fertilizers, what should I be looking for?

 

[Shibui]

I don't have any experience with liquid fertilizers, what should I be looking for?

Doesn't matter. All fertilizer should have nutrients and trees can't read so they don't really care where their nutrients come from. Any liquid fertilizer will be better than no fertilizer.

 

[TheRollercoaster]

Given that sand doesn't have nutrients, should i repot them at some point? Supposing i start fertilizing and they grow somewhat, i guess at some point they will require more than just sand. How do I know when to do it? Can they get over winter in sand so i repot next spring?
Perhaps I could plant the entire thing in some organic mixture, without breaking up the sand substrate and mess with the roots. I made some holes on the bottom of those cups.

 

[Shibui]

Most of the potting mixes we use have very little nutrients. Some people use completely inorganic materials for potting mix which has almost zero nutrients. All potted plants need added nutrients to cater for the small pots and the types of potting mixes used. In bonsai we tend to keep our trees in smaller pots which need watering often and watering leaches soluble nutrients so as bonsai growers we expect to need to fertilize more often than most other plant growers and certainly much more often than plants grown in garden soil where nutrients are recycled and constantly released from organics in the soil.
You may be able to work out a better potting soil for your needs but for now, focus on rectifying the nutrient deficiency and try to get used to the idea that some potted plant pursuits will need regular added fertilizer in order to maintain plant health.
There should be no problem overwintering in the existing sand provided you maintain adequate fertilizer and water until then.
Equally, small seedlings can be repotted almost any time. Your seedlings are about the size where I normally prick out seedlings into individual pots and I will do that whenever the seedlings reach suitable size rather than time of year. Young seedlings are programmed to grow new roots as a matter of urgency so they can cope with repotting where older trees of the same species may not.

 

[TheRollercoaster]

Thanks for the comprehensive reply, really helpful.