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Bonsai Soil and Pots

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Bonsai soil and bonsai pots: Tips for a healthy tree

The soil you use affects rooting, feeding, watering and transpiration; it is where half your tree lives so this is our second biggest consideration in maintaining your bonsai. While the needs of individual species vary greatly a good rule of thumb is 30% grit, 70% humus for deciduous trees, and 70% grit, 30% humus for evergreen needled plants, but these are just general guidelines.

Hemlocks, for instance, are an evergreen needled tree that likes 70% humus and 30% grit, but the pines like even more grit than the 70%; purists in Japan grow pines in 100% sand. Find a soil that fits your watering schedule and your tree. While I have used commercial bonsai soils, the best tool purchase I ever made was a set of soil sieving screens. I now make a custom soil for each of my plants as I repot, adjusting additions of exploded clay, marble sand (these are my grits), peat moss, pine bark, cocoa mulch and compost (my humus).

The smallest screen allows me to screen and dispose (in the compost) allsoil the fines in any soil components, the largest takes out all the debris too big for soil, and the remaining screen sorts my soil into a larger grade for the bottom of a big pot, and a smaller grade for the top of larger pots or for the entire depth of smaller pots (they dry out quicker and less porosity means slower drying. The shallower depth of small pots also means gas exchange is not a big a deal). The same basics apply for the tropicals, with a 70/30 humus/grit mix (with some of the more water hungry tropicals like ficus I substitute pine bark for grit and go for a 50/50 mix). Again, much like the watering process, watch your plants carefully and determine their individual needs for yourself.

Bonsai Pots
The bonsai is our main display, but the pot is our main means of displaying it, so the choice of a pot is a crucial one to our bonsai’s appearance. I have yet to buy a commercial grade tree (I can’t afford the artist grade trees) that I didn’t think needed transplanting. Usually it was the soil mix (beware of glued down rocks), but as often as not I was in a hurry to get it out of the ugly container it was in and into something more appropriate (I’ve had dates just like that, too…).

The ideal proportions for the pot are as follows. It should be 2/3 to 3/4 as wide as the tree is high and 1/2 as deep as the tree is high. The height of the pot should be roughly the same as the diameter of the trunk; while first establishing trees this last rule should relax a little. The dimensions given are for showing trees; when I’m first styling and changing the structure of the tree I don’t think about repotting and there are more than a few trees I still have in nursery containers despite the fact that I have had them for five or more years!

Bonsai Pot color considerations
Colors are our first concern with pot choice. Muted earth tones work best with most plants, although flowering varieties can be accented nicely with a glazed pot in an appropriate tone (Many of the pots I see today are in colors more appropriate to a Matisse painting than bonsai pots; avoid these at all costs). Glazes work better with tropicals; they are usually as hurt by freezing as the tree in them and so many of the tropicals flower as well, making colored pots less obtrusive.

Unglazed pots are more rustic and earthy and the dark brown and reddish tones of earthenware are perfect foils for green foliage; while I own many glazed pots they are all sitting on the shelf sans trees. ALL my trees including my three foot tall tropical ficus are in either Japanese brown mud pots or Chinese red clay. But pots like trees are a matter of personal taste, so find a pot that suits your tree and your taste.

bonsai potTake a new look at that bonsai
Think about more than just the size of your tree. Trees are often said to be masculine or feminine; Japanese maples are feminine (slender, curved trunks with a smooth bark and finely cut, delicate branching and leaves), and black pines are masculine (squat, chunky trunks with craggy bark and solid, dense branching). You get the idea.

Look at your tree and decide if it’s a boy or a girl. Masculine trees look best in dark, squares and rectangles and feminine trees look best in ovals and rounds of a slightly lighter shade. Remember that some species need more moisture so a taller pot (up to twice the recommended depth) is appropriate. You will often find pots three times as tall as they are wide or deep; these are cascade pots and should only be used for that style (wide, flared hexagonal and octagonal pots are sometimes found and are more appropriate for semi-cascade than the cascade pot). Let good taste be your main guide.

  • Old trees with old pots, new trees with new ones.
  • If it’s a three legged pot, one foot faces forward.
  • Leave used pots out in the sun to sterilize them.
  • Reds and browns with green, brighter color with flowers, Pines in earth ware!

bonsaiRepotting
Don’t rush to get your new tree into a pot as soon as you shape it (I find that one big project at a time is all most trees will tolerate). I killed more trees when I first started out trying to create instant masterpieces. I would take a nice piece of nursery stock, and in four hours I would prune it, wire it, repot it and then wonder why it dwindled away on me despite my careful considerations.

Bonsai is an art form of patience more than anything else; while any suitably pruned plant is dubbed a bonsai here in the States, in Japan the tree must be in training for seven years before it earns the title. So if it’s still going to have the training wheels on for six more years, there’s no reason to try to do everything in four hours! But they all need repotting eventually, so here’s the way we do it… (in spring, hopefully, but never too close to winter, anyway…)

  1. Assemble everything (preferably outside; this is messy) you need to complete the task. Shears, wire clippers, a knife, a chopstick (Uh huh…), bonsai wire, drainage screens, watering can or hose, spray bottle (you can skip this one if your spray nozzle on the hose has a mist setting) your new soil and the tree in question.
  2. Put your drainage screens over the two drainage holes
  3. Cut a piece of bonsai wire twice the width of the container and thread it through the drainage holes and screens (Go to the inside of the screens or when we put tension on the wire it will pull the screens in, and your soil will fall out the drainage holes) If the pot only has one hole, cut the head off a nail and use it to wrap the wire around. Then thread the two ends of the wire through the hole and through opposite sides of the screen. Now in both cases, pull your wire over the side of the container and out of the way.
  4. Using your coarser soil, make a mound in your container where you are going to place the plant. (You should never place a plant dead center of a pot. Always offset a little to one side and a little towards the back) Some very shallow containers demand mounding the soil twice the depth of the pot, so keep that in mind.
  5. Now remove your tree from its old pot, cutting the old wire that holds it and running a knife around the edge of the pot to separate the root mass from the container.
  6. Comb out the roots with your chopstick removing most (not all) of the old soil. I like to leave a little of the old soil as long as disease, fungus or insects aren’t in the picture. Certain microbes in the soil are beneficial to your plant and colonize the soil around it. Leaving a few with the tree helps re-colonize the new, fairly sterile soil you are replacing it with and I feel benefits the plant in overcoming the shock of transplant.
  7. Prune the old roots (usually a 1/4 to 1/3 of the root mass and never more than ½ at a time). If they start to dry at ALL, mist them thoroughly.
  8. Work your tree down onto the mound of soil, eliminating air pockets. Mist the roots.
  9. Back fill half the depth of the pot with your coarse soil and then bring the ends of your wire in and, enclosing some main roots close to the trunk, twist the ends TIGHT to firmly secure the tree in the pot. Cut off excess wire. Mist the roots.
  10. Finish filling the pot with your finer soil. Use your chopstick to work soil under the root ball and down to the bottom of the container; this eliminates air pockets that can dry out your roots and kill them. Make sure your root buttress (where they flare out) is visible. In our shallow mounded pot the buttress should be above the edge of the pot.

11. Moss the top of your pot. I collect my own from around the yard, but I am blessed with tons of the stuff. Florists carry sheet moss that will do nicely. I secure it to the soil by cutting an inch of bonsai wire, shaping it into a fishhook, and pushing the long end through the moss and into the soil. Four or five of these will tie things down nicely. This is an optional step unless you have one of those shallow containers and then you’ll need the moss to hold your mounded soil.

12. Now water the plant thoroughly (I recommend not using the immersion method here as your new soil is still very buoyant and will make a dash for the surface, undoing all your work. Watering three times is a much better idea for a newly potted plant and waiting an hour between each watering is best yet.

Voila! You have just repotted your first (of many) trees. Remember that watering is very critical right now. The poor tree has just been ripped, cut, knifed, CHOPSTICKED, and then thrust into a new soil it has little connection to, so it needs lots of watering as it is going to be able to access very little of it. Soil should remain moist but not soggy; root rot is lurking here, too.

Remember I mentioned the little microbes that can help our plant with shock. Well, you can buy them over the counter now; they are generally called mycorhizal supplements, and you should be able to find it in your favorite garden center. Your plant stands a much better chance with some help like this.

Another old English trick to promote root development is to allow willow stems to sit in water for days (or weeks), and then water with the willow water. It may be an old trick but there is good scientific evidence to back it up, and willow twigs cost a lot less than mycorhizal supplementation. (I am not suggesting that one replace the other).

Keep the plant in a little less sun than normal and keep an eye on it. It will sulk for a bit (maybe even a week or two) but then the first new shoots will appear and you will begin to notice that the pot is drying faster than it has been. Your tree has turned the corner and is now ready for regular rotation. You can now feed with whatever fertilizer you have chosen; I like natural fertilizers like seaweed and fish emulsions or manure tea, but the chemical stuff will work too. You can fertilize bonsai a little more often as the soil is more porous and it gets depleted faster (There’s less of it supporting the plant than normal garden situations). Regular fertilization will cause back budding and help fill in the foliage, so we have to look at pruning now...

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