Mix your own soil using durable, gritty, and porous ingredients, such as Turface,
Pumice, Perlite, quartz, granite, and pine or fir bark. An easy recipe to follow is:
1 part turface, 1 part bark, and 1 part granite. These ingredients should be screened
to remove the fine particles. For the Turface, keep any particles larger than 1/16 of an inch.
For the bark and granite (or quartz, gravel, et cetera), keep the particles between 1/8 and 1/4 inches.

You'll need to provide all the nutrients for your tree, so choose a complete fertilizer
containing the micro-nutrients. I prefer Foliage Pro 9-3-6.

Josh

I do not recommend rocks for drainage because a layer of rocks in the bottom of the container will not
promote drainage. It will actually impede and delay drainage. I can explain further if you wish.
But the short answer is definitely no rocks ;-)

The amount of roots that can be removed during re-potting will depend on a couple of things:
first, the type of plant (how much genetic vigor does it have). After that, you need to perform
the root-pruning at the right time of year, which is also directly tied to the vitality of the plant.
In other words, if you time the re-potting with the best growing period of the season, then your
plant will recuperate much better. Healthy, well-grown plants will tolerate most stresses better.

My advice is to post a pic for everyone to see :-) There are many folks here who would love
to offer suggestions, and who might be able to help you locate ingredients for a mix.

Josh

Looks to be a Juniper, so it'll really need to be kept outdoors.
I like what you've done with the plant so far, and I think you'll have many fun years
of pruning ahead of you :-)

When Al sees this post, I'm sure he'll add a few pointers on root-pruning/timing.

Josh

Where DO you live, Katie? I ask because the timing of repots is usually affected by geography. Do you have a lot of examples of this particular plant in the landscape where you live? I wouldn't expect J procumbens to be too happy in zones much above 8.

Al

As for kitty litter being used as a soil component.... as far as I'm concerned its unheard of in the states. I know a few people in other countries using it but I think the brand used is not offered in the U.S. Your typical kitty litter if used will turn to mush and then upon drying will turn your soil and the trees roots along with it into a cement brick. A good test of taking a small handful and placing it in a glass of water will show you that within a day if not hours the litter will bloat up absorbing the water and become goo.

When it comes to repotting and root pruning (assuming your tree is healthy and growing vigorously) you should remove up to 1/3 of the root mass at the most. When concerning deciduous trees in climates where there is a winter, repotting and any general heavy pruning is best done in late spring or early winter right before the tree has started to break its dormancy. This will ensure the least amount of stress is being incurred on the tree.

The metal mesh on drainage holes are only meant to keep the soil from being washed out the bottom of the pot when watering. While some metal is adequate for use as drainage netting I would recommend using the plastic type sold for bonsai use as some metal ones will rust and can also release toxins into the soil killing the tree.

I think that covers just about all of your questions??

-Mike

I have no experience with growing trees, especially a juniper in your climate and cant say whether it can be done nor how it should be. Your best course of action would be to seek out your local bonsai (which California is a mecca for)club for members advice and take a trip to your local library and read up on as many Bonsai books as possible.

I would do my juniper repotting (in your zone) in March. When soils are warm enough, junipers tend to start to wake up and take off when nights are shorter than days, so just after the vernal equinox would be a good time.

The soil recipe Josh suggested would be a very good choice for you. Commercially prepared bonsai soils usually contain too many fine particles to offer the highest potential for best plant vitality; this, because of the perched water that remains in the pot .... which can be directly attributable to the fine particles. The reason I can say it should be a very good choice is, if you have all the ingredients, it's easily adjustable for water retention. By varying the volume of Turface in the soil in relation to crushed granite, you can go from a soil hat holds moderate amounts of water to a soil that holds a significant amount of water - all without having to suffer the consequences associated with water held as perched water.

If you're confused about any terms or about how to approach the soil issue, just ask. One thing a budding bonsai artist needs to understand is the subject of soils; another is how plants work (physiology). Many people come to bonsai, and nearly as many exit the ranks due to the frustration of not being able to keep their trees alive. A basic understanding of soil science is probably as important as anything you could learn about bonsai, but it's a simple concept that can be absorbed in an hour or two. The physiology part is a bit more arduous than learning about soils, but you can catch a break by getting the soil science down first, because it will buy you the time you need to work on the physiology.

Best luck to you!

Al