There are really two bonsai topics that I hesitate to write about. One is soil and the other is fertilizer. The cause of my anxiety is two fold. first of all, I’ll be the first one to say that I really haven’t studied these two topics to the extent that I have read, watched, and taken classes about some of the other topics. With my own trees I haven’t had a lot of hands on experience with either as well. I’ve never mixed my own soil, and my fertilizer regiment is essentially green dream slow release once a month. Secondly, the topics are both incredibly susceptible to argument, criticism, etc. Essentially everyone has their own ideas about what is the best technique (my suspicion is that 80% of the variance doesn’t really make any difference what so ever). As we all know, this community of ours tends to attract those who are ever too eager to argue about “who knows best.” and I’m not interested in being a forum for that. There are plenty of those….
But alas! Though I didn’t choose to write about dirt, dirt sort of chose me. In my neck of the woods (right outside D.C.) its been a very weird growing season. I feel like every time I turn around it’s raining. As I may have discussed in an earlier post, unfortunately my tendency is to over water, and I fear that this year I have inadvertently pushed some of my trees down the wrong path. I’ve been getting yellow-falling-off Juniper foliage and similar pine needles. This is no good at all, and it’s taken some drastic measures to get things (sort-of) back in order.
I think we should really go back to the beginning. Sometime in the fall of 2011/early 2012 I began amassing a collection of “bonsai.” I’ll be 27 in December and as you may imagine my funds are strained, which is not particularly conducive to an expensive hobby like bonsai. But I really love growing little trees, and as a result I set out to do what I could with what I had, and now I have somewhere over 40 little green mounds on my porch.
My collection consists of probably 40% trees from “bonsai focused” sources, 45% regular nurseries, and 5% trees I’ve collected (mostly seedlings). This means that the majority of my collection was not raised with bonsai in mind, and thus is currently growing in non-ideal nursery soil. You can tell that at least some effort was made with some of the conifers, to put them in a mix that contained a bit more grit than average. And in a few cases submersible pots were used in an effort to increase drainage. Even many of the trees from bonsai focused nurseries were planted in soil that I felt wasn’t really ideal.
But I was relatively new to bonsai and thus scared to repot. It can be scary! I mean you’re essentially gambling with how much of the plants life giving material you can remove without seriously injuring or killing the plant. There are plenty of trees that I know of where you can essentially cut off every branch and the tree will survive. There are significantly fewer that I know of that can survive all the roots being cut off! But if you have a little luck, a little knowledge, and a little confidence, you don’t have to be scared of repoting. In my case I pushed the limits of how long I could leave my trees in bad soil, and I’m certain that I’ll pay the price next spring.
So what should you do to keep your trees healthy?
1. If you’ve recently purchased a tree from a non-bonsai source, repot within a year of purchase.
2. What are your short term and long term plans for the tree? A good rule of thumb to follow is that you can either repot or do a total restyling of your tree, but not both in the same year. Obviously the longer you have a tree, or have worked with a species of tree, the better idea you’ll have about what it can take. Until then, keep it simple.
3. Do your best to plan your repot for the early spring (March-April where I’m from). If that doesn’t fit your timeline a good alternate would be early fall (September).
4. If you’ve recently repotted, Hold off on doing any substantial work on top of the tree until you know your tree is doing well. During the growing season it should take 1-2 months for you to get a good idea about how the repot went. Some species like pines and junipers can stay green a long time after they’re suffering. If you don’t believe me, cut off a branch and see how long it takes to turn brown. Hold off on any work until the next growing season if possible.
My earlier trepidation in regard to repoting has more or less forced me to do a substantial amount of fall repoting over the past couple of weeks. If you think repoting is in your future there are a few important considerations. First and most importantly, what stage of development is your tree in? The question to ask yourself in order to figure this out is: are you happy with the overall size and trunk size? If you are happy with the size, then you’re probably moving into the Refinement Stage. If not, you’re in the Development Stage.
This crucial distinction should guide every action you take with your tree. If you’re in the refinement stage, the considerations you take when repoting will probably be guided by your concerns for aesthetics and long-term sustainability. In the development stage its important to use larger pots so your tree has room to run and grow exponentially faster. I’m sure you’ve seen pictures of various improvised pots. Everything from terra cotta garden pots, to homemade wooden boxes, to spaghetti strainers. Regardless of the device, the strategy is to maximize growth at the cost of root size. If you want a larger tree with thicker branches, this is the way to go. Even many refined trees are cycled between “grow pots” and “show pots” to help maintain their vigor.
But I digress. Back to the topic of soil. what do we fill the pot with?
For the purposes of bonsai, soil should be broken-down into two logical categories: Water retentive (WR) and non-water retentive (NWR). In reality, the water retaining qualities of various types of particulates land on a spectrum. Nothing is black and white. But for the purposes of this explanation of soil, let’s pretend that they are. The central idea behind blending soil particulates to create the “perfect blend” is to make a soil that is both well-draining and will provide the perfect mix of moisture and air (yes air) for your trees roots.
My problem which kicked off our discussion of soil, came from my trees being in a soil blend that had a high WR particulate concentration. Essentially the soil held on to the water for too long and drowned the roots. And my remedy for this was to replace as much of this soil as possible with a higher concentration of NWR soil. On average bonsai professionals use very high NWR soil. Initially it may puzzle you. It’s not as if their trees like it dryer than our trees.
The reason is control. You have more control over how much water your tree receives and when it receives it with high NWR soil than with high WR soil. No day is the same. Length of daylight, temperature, humidity, wind, position of tree, size of container, type of tree, time of year…( you get the point, everything effects how quickly the soil dries out). Some days your soil will stay wetter longer, and on others it will dry out quickly. The problem is, you can never make your tree drier, only wetter. So if you’re suddenly hit by a cool streak in the summer, followed by lots of rain, your trees run the risk of staying soaked for extended periods and possibly getting root rot. With NWR soil, you’ll always be safe, because you’ll always have the problem of having to apply water (which you can fix) and not the problem of having to remove water (which you cannot).
Many people, especially novices, will prefer to use a pre-blended bonsai soil. Many bonsai nurseries and online stores sell their own proprietary blends. In many cases they will even offer multiple blends. Sometimes the blends are differentiated for deciduous, conifer, or tropical trees. In other instances they may be differentiated by the tree’s size class. One soil for shohin (smallest trees), one for Chuhin (medium), and one for Ogata (large). If the Soil is divided by family classification, it is likely that the differentiating factor is water retention. Tropical soil blend would hold the most water, deciduous would hold the second most, and the conifer blend would hold the least. If the blends are divided by size class, the mixes likely use the same general material blend, only with differing particulate size. In this case the Shohin blend would have the smallest particles and the Ogata would have the largest particles.
I haven’t yet delved into blending my own soil. Mainly for lack of time. But if you’re looking for a guide, this PDF from the bonsai learning center is a good place to start.
Have a safe and successful fall repoting season!