AusBonsai

Hi guys,

So yesterday I dug up my Chinese elm which is looking fantastic. I went and bought a premium potting mix and mixed in some bonsai soil. The problem I’m having is that it isn’t well draining… at all. It pools and takes forever to sink down into the pot.

I read somewhere that elms like well draining soil so, my question is, is it too late to quickly repot again with better draining soil or, just leave as is and hope the soil isn’t detrimental? Is the current soil even detrimental? The internet has so many conflicting theories.

I’m a complete beginner so any help would be amazing!

Thank you

EDIT: I should mention that no, it hasn’t gone into a bonsai pot, just a black plastic pot for recovery and shaping for the future!

What sort of pot have you put it in? Is it a small, shallow bonsai pot or a training pot or a large plastic tub etc. A photo would also be very helpful for others to have a look at, to give you the best advice (needs to be less than 1Mb to upload here).

Definitely not too late to repot a day or even a week after you've already just potted it, you won't do any additional harm than what you might have already done by moving it (unless you jammed it in there). It's not going to settle in within 24 hours.

What does the bottom of the pot look like? Does it have sufficient drainage holes? Did you put gauze or something similar over the drainage holes so they aren't clogged by whatever material you planted the tree in.

Be aware that "premium" in terms of potting mix is just a marketing word. There are potting mixes out there labelled premium that aren't very good.

Everyone has their own thing, but personally if I have space in a pot (that depends on a number of factors) I will put a layer of something larger on the base of my pots like crushed tile or some other larger material to allow the very bottom layer of the pot to drain super quickly.

Thanks for the reply!

So I would say a large training pot. A black plastic pot. I haven’t placed any gauze or anything else to the bottoms of the pot. I’ve attached a picture. I hope that helps!

EDIT: What type of soil would you recommend? Should I give it a little bit of seasol as well to help with root growth or just leave as is?

With those pots, I typically cut them down a bit to reduce the amount of depth. More soil = more water retained.
Unless you are using very dense or compact soil, it's not likely that is what is causing the water to pool. It's more likely the water can't get out the drainage holes. If it were me, I'd trim the pot down a bit and add a layer of something at the base of inside the pot to allow the water to drain more easily.

As far as what to use for soil, you will get different answers from different people. If you can, update your profile and/or mention here where you are located and hopefully someone from that area can give you their suggestion. I'm not the best person to ask because I don't have an opinion and I just use what works for me. Currently I'm using a mix of coarse sand and premium potting mix and crushed brick,tile or scoria at the base of my pots.

To be clear, there are some premium potting mixes which are decent.

Thank you so much for your reply! I greatly appreciated it! I never thought about cutting down the pot size. That’s a great idea. I can only buy the long pots here and I have tried to find shorter pots so I appreciate that idea.

Also sorry about the location. I didn’t know i could update my profile for that sort of things. I am based in Perth Western Australia so very hot and dry summers with wet, if we’re lucky winters.

Thanks again!

Cutting down a pot will not help drainage. It could make the problem worse.
Adding a layer at the base does not usually assist drainage. It often makes it worse.
All potting mix will hold a certain saturated layer at the base. That's where gravity = adhesion and cohesion of the potting mix and is known as 'perched water table - 'PWT'.
Adding a layer of stones at the base only lifts the perched water table higher into the root zone. Reducing pot height only moves the root zone down closer to the perched water table. Both case problems by allowing less well aerated soil for the roots to grow in.
Potting soil with smaller particles usually has a deeper PWT. Potting mix with larger particles and more spaces generally has a much shallower PWT which is why we usually use bonsai mix with larger particles in our shallow bonsai pots.

You can solve the water dilemma two ways -
Leave the potting soil as is but water less often to allow the soil to get close to dry before watering again.
Sieve out the fine particles to make the soil drain better.
I'd probably go for the second option as it allows some room for error with over watering.
Repotting a few days to a week after root pruning won't hurt as the new roots won't have started to grow yet.

If you're growing in a pot and potting soil anyway, could soil additives help?

I'm new to bonsai, but I'm a long term container gardener. When I have plants that need drier or wetter conditions I add things to the potting mix.

Things like grit, sand, or pumice can help your mix drain better. Grits not a great long term solution for bonsai as I understand it, because it becomes very heavy for larger trees, but it's probably fine for a tree in development. I use grit, sand, and perlite in most of my potting mixes for cacti, aloes, olives and sage down here in rainy Melbourne.

If you're repotting anyway it could be worth mixing the soil with a bag of one of these, they're pretty cheap at any nursery or the big green shed.

Happy to be corrected by the more experienced growers here if I'm wrong about that though.

My Chinese elm which I'm also growing in a black garden pot is in a mix of roughly 50%potting soil, 25%sandy seedling mix, and 25%perlite. It's one of my first trees, but it's growing pretty happily so far and it's been relentlessly rainy on the east coast.

Ok, apologies, I can see what you're saying.

Adding a layer of tile or something similar that leaves gaps between is impossible to raise the water table. That's hilarious. Air can't support water my friend.

In that case why does any water stay in a pot. The pot has air under it my friend but there's still water in the soil. It is not air supporting the water. It is the cohesive forces holding the water around the soil particles that supports that saturated layer.

You can see this in action with an ordinary dishwashing sponge. Saturate the sponge. The water will flow out of the sponge until cohesion = gravity. Drainage stops but there's still water in the sponge, even if you hold that sponge up in the air. Prove it by squeezing the sponge.
You can also show the perched water table effect. Saturate the sponge and lay it flat. Water drains out leaving a thin perched water table. Now gently turn the sponge onto one long side. More water drains out until the same perched water table is achieved. Now gently turn the sponge onto one end. More water drains out until the same PWT is achieved where gravity = cohesion again.

Well so I jumped the gun and repotted. I did cut the pot down a bit. I guess this is to keep the roots closer to the tree when getting towards the bonsai pot stage? I placed some gravel in the bottom, just a thin layer and used much less potting mix with some sand and native mix we have here which is great for drainage.

I guess I’ll have to leave it for now and hope it survives.

Is the rule of thumb wait 6 weeks until you start to fertilise?

My poor elm! She was going to be such a beauty out on the verge but, I’m a firm promoter of natives so out she came and in with a eucalyptus.

The trunk is very nice on the elm and it really did flourish there. I’ve noticed many elms as the tree of choice down at the dog park. Hardy buggers!

Thank you to everyone for your help!

Shibui it looks like the post yiu are referring to has been edited / deleted.

But you are correct.

Water particles are hydrophilic (attracted to themselves) as is soil (ie attracted to water), so in simple terms there will be water retained in the pot even if you have it hanging and 100% humidity (ie it won’t just drain out).

In essence, it is how capillary action works.

But I will say, from my engineering studies, water is a very complicated fluid, especially how it interacts with soils. I am no means an expert, I barely understood the issues (it was voodoo science to me), but I understood enough that it isn’t just gravity.
, but from my experience, I agree. Having larger particles doesn’t improve the drainage, especially with time. Large particles tend to get clogged up and therefore end up with worse material (for drainage) than had you not used anything.

Getting back to the Elm, you state you dug it up. Did you remove all the garden soil? Did you do a major root prune? All this information will help. A quick repot after a repot early in the season. Would generally not worry a tree too much. Should it effect the tree, it could lose some or all of the fresh spring growth. Having said that don’t panic for a tree like an Elm give it a few weeks and it will re sprout. The other issue pending the soil you purchased, some are full of fines/dust and if the bags are old or have been left under cover the soil drys out and becomes hydrophobic. In this case the water takes an age to drain thru the pot. If you sit the pot in a tray of water and allow the soil to start to hydrate it will come good. It may take a few days of sitting in the water tray to work. Or you can water it with some of the re hydrating products that are on the market. The other issue If you find that the pot is staying too wet you can also drill some holes in the sides of the pot at varying heights to remove excess water.
I know you have now repotted it, so hopefully it all settles.
Cheers
Kirky