Hey, I've got a young jap maple and a chinese elm placed outside of course. Im wondering if it should be just under the open sky or shoul they be roofed or something. Im especially curious what happens if it starts to rain. Is it okay for them? What if I water them in the morning and then it starts raining all day long. They potted in a well draining soil mix with draining holes.
My other question is how do I see if any of my bonsai needs watering if their soil is all covered with moss?I can't check if the top of the soil is dry or not.

If the soil is well draining you have nothing to worry even if it rains the whole week. I have a well draining soil and, to be sure, in the hottest days of sumer I water my pines 3 x/day and have no problem at all. The only negative side of this is that heavy rain will wash out of the soil the fertiliser. This is why I'm fertilising with liquid fertilisers.
Moss is not desired when training a tree - it is mostly used for shows (placed on the soil only for that occasion), so I suggest you remove it even it is good looking. It makes it hard to feel the wetness of the soil and reduces the oxygenation of the soil/roots.

Madartej21 wrote: ... .. Im especially curious what happens if it starts to rain. Is it okay for them? .... ...

The Rain ... It's about the best thing that could ever happen. Did you ever notice, when you water your tomatoes, all summer long, and they just won't grow. Then a little T-Storm rolls by, only about a half inch of rain. Then those tomato plants go wild (trees do the same, only in slow motion). Without going into to much detail. ... . The rain, sort of dumped a bunch nitrogen (the main ingredient, in our atmosphere) on your plants.
Just imagine, if a bunch of tornadoes, kicked up dust all the way across Kansas. ... . what a bonus of nutrients.

Just have good drainage, next week, you'll have another problem, and miss watering

My trees in the summer are watered regardless of rain. Some of them have a canopy, under which very little rain will get so I have to water anyway. Rest of the year is different. If the trees get very wet then you can tilt it with something under one side of the pot to allow the water to drain. Some species need to be kept drier and are placed under open cover.

Moss is perfect it keeps the substrate from drying too quickly on hot days.
If the moss is wet, the substrate is for sure wet.
If moss gets dry, the substrate under it is starting to dry out too.
Anyway, it is easy to pick up the moss and check under it as it has no real roots.
Moss rules.
I want more of it!!!

Krištof wrote: Moss is perfect it keeps the substrate from drying too quickly on hot days.
If the moss is wet, the substrate is for sure wet.
If moss gets dry, the substrate under it is starting to dry out too.
Anyway, it is easy to pick up the moss and check under it as it has no real roots.
Moss rules.
I want more of it!!!

HA!... I only have one tree with moss. So you could say I have uno moss.
Both my maples are under a huge cherry tree on my property. It's been advised to shade them in a large tree during hot summers. I water all trees unless it's actually raining when I go to water.

Good question, good answers. Great forum!

About moss: I'm going to agree with Kristoff and Simply. I don't mind moss in my pots. It doesn't prevent aeration and it doesn't stop water from penetrating the soil.
It does keep the top surface moist, which is good for roots at the surface. Watering is no different, I water the pots with moss the same way as the ones without.

I do not want moss on the trunk though, especially not on my pines and my new juniper, that have plated bark that can come loose when trying to remove the moss.

Here's a link: "The Moss Myth"

Auk wrote:
About moss: It doesn't prevent aeration and it doesn't stop water from penetrating the soil.
It does keep the top surface moist, which is good for roots at the surface. Watering is no different, I water the pots with moss the same way as the ones without

When I had moss on the soil when watering, the water just run off the moss, so I had to come back to the same tree watering it more than once.
Regarding it keeping the soil wet - for this I use lava rocks on the surface (2cm layer). It keeps the moisture very well as it absorbs the water and it prevents the soil from being moved by water. Its also very easy to remove and check the humidity of the soil. I did this last week and saw that the entire surface of the soil below the lava rocks is covered with small roots (and were talking about a pine transplanted from nature last year, that had very poor roots).
So Im still against the moss, but it is true that once you get to know your tree you can tell if it needs water or not.

That is true, sometimes you got to water twice for moss to soak up water cause sometimes it just runs off it, but that don´t happens when you pour steady stream of water on it for a while. I understand you cannot water like that inside for example.
Good that lava rocks work for you, that is not an option for me as I have most of the trees planted on rock and marble plates with the hills that needs to be covered with moss or they would be washed off

Krištof wrote: I have most of the trees planted on rock and marble plates with the hills that needs to be covered with moss or they would be washed off

And you think that you can write this and not post a picture?! Go take a picture and post - we will wait.