There are many factors, other than the main subject – a plant, which contribute to make a genuine bonsai. The next few sections of this part of the homepage cover these other factors, including using mosses, and alternatives to mosses as ground covers, using ornamental rock or stone with bonsai and an explanation on bonsai pots and containers.
There are functions for everything in bonsai, and mosses and lichens, used as ground covers, are no exception. They, of course, look great, covering the soil surface with ‘green velvet’ and helping to retain water while holding the soil in the container. For people buying bonsai, the presence of moss is always a good sign. There are a great number of types of mosses and lichens and these can be mixed to provide a very effective result overall. When not used for ‘conservation’ purposes, they should be planted sparingly so that their effect is natural, and they do not prevent water from reaching the soil. There is a particular method of mossing a potted bonsai that will produce a smooth mat of deep green, with none of the lumpy growth that can be typical of piecing bits of moss together. With a sharp knife, slice the moss from its growing place, taking as little soil as possible. Put this moss in a container lined with paper, and moisten it lightly (it should be moist, not wet). Remove most of the remaining soil from the moss using sharp scissors, pulling each little tuft away from the larger piece. Prepare the surface soil in the bonsai pot by scratching it to roughen it up. With long handed tweezers, start inserting each tuft of moss close to, but not against, the trunk. Work out and away from the trunk until you have the look you want, then brush off most of the tufts. Sprinkle dry soil over the moss and press it down with a flat spatula or small trowel (even your hand if you are careful). Mist gently two or three times and the soil will settle down between the tufts. As an alternative to collecting moss and going through this somewhat time consuming process, you can use dried moss. Gather it, then place it in the shade for a few days until it is completely dry. Put it through a fine strainer – a sieve will do – to crumble it. Mix the particles with some soil and spread it over the bonsai soil in the pot, making a thin, even layer. Press it down with a flat spatula or small trowel and gently mist continually until the soft green moss begins to grow. Some people just scrape soil off the bottom of the moss and put this on the soil of the bonsai, but takes a much longer time to root and is a delight for small birds when looking for worms if left exposed. Along with the growth of a healthy crop of moss often comes the appearance of a silver fungus around the soil line at the trunk of the tree. This is a sign of a healthily growing bonsai. The fungus develops as the moss takes hold, and it cannot be artificially implanted. In the heat of summer, moss may turn brown. Do not despair – it means the bonsai is getting the water it needs. As soon as cooler temperatures and higher humidity return, so will the ‘green velvet’.
If you want to increase the impact of your bonsai, introducing one or more rocks is a good idea. Solid, elemental-looking rocks can give the impression that a bonsai is part of a landscape. A single rock can resemble a rugged cliff, a towering mountain, or a rocky island. A group of smaller rocks, positioned as outcrops protruding from the soil of the bonsai container, can recall the rocky terrain in which the tree lives.
The use of ornamental rocks with a bonsai tree was always something of great importance in ancient times. This practice has become less used these days, but can add just that one final touch to your bonsai masterpiece. Excessive use of rock and statues around a bonsai is known as Saikei, but a single one or two rocks along with the tree still classify as a bonsai.
The choice of what type of rock to use basically is up to the bonsai artist. Personally, I use interesting and weathered pieces of granite and slate that I have collected from the wild, but you could basically use anything that looks natural and suits the type of tree for the bonsai, and the pot. Note that if you are going to use rocks collected from the sea, or estuaries, that these have been exposed to the elements for two years at least (such as in a corner of your garden) where this has allowed the salt and any other chemicals to leach from inside. If you do use a rock that has been exposed to chemicals or substances that are detrimental to your bonsai – either do not use it, or make sure that these substances are properly eliminated.
For your rock ‘planting’ you obviously need to find a beautiful rock that is harmonious and complimentary to the tree’s structure and colours. Many types of rock exist around the world, but some are better than others for bonsai. The best kind for bonsai work is a hard type that will not crumble away. It should also have an important colour, shape, and texture. Pay particular attention to the rock’s shape and type. It should be intrinsically interesting. A round, smooth rock, for example, suggests a watery scene, so it would enhance trees such as willows. A bland rock is unlikely to produce a good effect. On the whole, pick a rock with a natural-looking shape, but you should not find this a limitation, because nature produces a wide range of fantastically contorted mountains, boulders and rocks. Pleasing texture and colour are also important: black and shades of grey are usually impressive.
A popular choice of rock is the Japanese Ibigawa rock. It is a volcanic conglomerate, a mixture of several rock types welded together by the heat of volcanic activity.
Do not use marble or quartz because their intensively shiny, glittering textures will detract from the natural effect of the trees. Frost may split the strata lines of sandstone and other types of sedimentary rocks.
You can use soft rocks such as lava rock and tufa, but don’t rely on these too heavily as they can erode quite quickly. Soft rocks should never be used for clasped to rock or root-over-rock styles.
When it comes to bonsai, it is not just the plant and its styling that makes the bonsai appealing to the viewer. The choice of the container that the bonsai is in is also quite important to the overall look and ‘feel’ of the tree. The container is as important as the tree in a bonsai design. Usually, growers select the pot after styling the tree, so that the two harmonise in shape, size, colour and texture. Practical and aesthetic factors affect the choice of pot. The purpose of the container is of course to provide suitable accommodation for the tree’s needs, but also to compliment its branch structure and seasonal or year-round colours.
The pot must hold enough soil for the roots to develop over a year or two. It should be frost-proof with enough drainage holes. Bonsai containers are usually shallow, but sometimes you may use a deeper one to hold a fruiting tree for example, that needs plenty of water to swell its fruits. (Never try to save on watering time by using a pot too large for the tree, as the roots may become waterlogged and rot.
It is said that unglazed, dark-coloured containers are usually chosen for classic bonsai or to impart a look of age. Evergreens such as conifers, look best in neutral brown pots, but glazed containers should be used for flowering trees or trees with unusual colours or characteristics. Pots of the colour featured above work well with plants such as Cotoneasters – with their bright red berries. Over the years, it has become traditional to select rather neutral shades of brown, grey and red for evergreens and the more colourful pots of green, blue and white for deciduous trees. It has also long been recognised, for example, that flowering trees look good in green, blue and deep purple pots. The exception to this is that trees and shrubs with red flowers look best in white pots. Fruiting trees can handle the competition of coloured pots and certain traditions have developed around them. For instance, it is considered the norm for trees with red fruit in white pots, and trees with yellow or orange fruits in blue pots. Basic brown pots are always correct.
Both evergreen and deciduous trees known for their highly coloured foliage follow the norms, with almost any vibrant colour looking well in green, red-leafed trees looking well in white, and yellow and orange looking well in blue containers. Again, the finishes can either be glazed or unglazed.
Generally, the more mature and aged the bonsai, the plainer the container should be. The more delicate the tree, the lighter in colour the container should be.
Feel free to chose whatever container that you think looks best for your individual bonsai, but as a general rule, oval containers compliment deciduous trees and rectangular ones suit evergreens best (particularly conifers). Hexagonal pots are softer in effect than other shapes – perfect for trees with arching or short and prominent trunks. The colour, weight and size of a pot should also be given great consideration, as well as whether it should have decoration or not. Larger pots are usually subdued in colour and texture, so that they do not dominate the tree. A smaller pot can be brighter. A container that is too overpowering, is too big, or is not the right colour, takes an enormous amount of the simple beauty of a bonsai away, and detracts from its overall aesthetic appearance.
Keep the container in scale with the tree: an individual tree should not look lost in a large pot, nor overwhelm a tiny one. A dense evergreen bonsai, for example, needs a deeper pot than a delicate maple. As a guideline, a mainly vertical tree needs a pot with a length between two-thirds to three quarters of the tree’s height. The pot’s length should be two-thirds and three-quarters of the overall width of a strongly horizontal tree. As a reservoir for soil and water, a smaller pot needs more depth in proportion to its width than a larger pot does. Certain styles and types of tree demand deeper pots.
One very important thing to remember when buying a bonsai pot is : never buy a pot with a glazed interior. It may look neat, but this drastically interrupts drainage and heat loss. The roots could rot very easily. Most good quality bonsai pots are very expensive, but it is better to pay more for a container that you know is good quality, than to buy a cheap pot that could turn out to be detrimental to your bonsai’s health. Some people might even want to use a slab of rock or slate instead of a traditional container to make a design look especially natural as an alternative to a pot for a forest planting or a bonsai that is spacious and dominating in design. These are usually granite, slate or volcanic rock, but can also be made from painted fibreglass and other materials quite cheaply.
Overall, the container of your bonsai should always suit your personal tastes – as you are the artist, but it also should compliment the basic design and layout. e.g. you would have to have a cascading bonsai in a tall, narrow pot. Remember, if you cannot make up your mind on what pot would suit the plant, experiment, and don’t be afraid to try something original. You can always repot the bonsai the following year into a more preferred style. Bonsai is a constantly changing process and one that requires a great amount of patience, but is never permanent.
One of the most widely debated subjects for most bonsai enthusiasts is soil composition. Ready-mixed soils can be bought from bonsai nurseries and garden centres but these tend to be relatively expensive. Faced with more than 3 or 4 trees to repot in the Spring, most enthusiasts learn to mix their own soils.
There are a large number of soil ingredients that can be used when mixing your own soil; different mixes are used by different enthusiasts with varying degrees of success. For the beginner, choosing which soil mix to use can be a daunting choice.
This article is written as an introduction to Bonsai soils, it does not discuss every soil ingredient or mix that is available, nor does it tell which soil mix is the ‘best’. That question can only be answered by the individual enthusiast after experimenting over time with his own trees and care routines.
The Basic Requirements Of Bonsai Soils
A bonsai is confined to a relatively small quantity of soil throughout the year on which its very existence depends. Through the soil in the pot, the tree must be able obtain water, nutrients and gases in order to grow. For this reason, the soil that the tree is planted in must be of the correct quality. The quality of the soil that is used directly affects the health and vigour of the tree.
There are two basic qualities that are required in a good soil mix;
- Good water-retaining and nutrition-absorbing capacity. Often provided by the use of dead organic matter/ Humus, the soil needs to be able to hold and retain sufficient quantities of water and nutrients for the tree to absorb.
- Good drainage. If excess water is not able to drain immediately from the pot, the rootsystem will be prone to rotting. Drainage is normally provided by the use of grit or small stone which keeps the mixture ‘open’, allowing excess water to pass through the mix freely. Good drainage also allows air to penetrate the compost, which is required by the plant.
Varying Soil Mixtures To Suit Different Tree Species
Though all Bonsai require free-draining, water-retentive soils, different species vary in their requirements for water and nutrients and this should be reflected in their soil composition. Pines and Junipers for instance require less water than most other species; this in turn means that they require a less water retentive soil mix.
Alternatively, flowering and fruiting species have increased water requirements and tend to be planted in soil mixes with relatively high water retaining capacities.
When mixing your own soil, the ratio of water-retaining material to grit is varied according to the tree that the mix is intended for. By increasing the ratio of grit to the mix, the soil becomes more freely-draining; by increasing the amount of water-retentive material, the greater the water-holding capacity.
Organic or Inorganic Soils
Soil mixes are described as being either organic or inorganic; both types contain grit to aid drainage but the water retentive ingredient(s) differ. Organic soil mixes are made up of dead plant matter such as peat and the ingredients are easily available at garden centres and DIY stores. Inorganic soil mixes contain no organic matter; instead, specially-formulated soil conditioners ranging from volcanic lava to calcined (baked) clays are used. These materials can be harder to locate, but, are available from good garden centres and bonsai nurseries.
Basic or Organic Soil Mix
The basic soil mix for bonsai has, for many years been grit and peat, mixed to a ratio of around 50:50. The peat holds water and nutrients whilst the grit provides drainage and keeps the soil open. The peat used is moss peat rather than sedge peat, the grit, either flint grit or crushed granite. All ingredients should be sifted to remove particles smaller than 2mm.
There are other organic substitutes for peat; leaf mould and composted bark are sometimes used along with other peat substitutes. Farmyard manure, garden compost or garden soils should never be used as they are of questionable quality and frequently carry soil-borne diseases.
The standard mix for bonsai is 50:50 peat to grit, but when repotting Junipers, Pines and other species that require a free-draining mix, the percentage of grit should be increased to as much as 75:25.
In the past decade, there has been a significant move towards inorganic soils. Though organic soils are cheaper and more easily available, they are also of inferior quality. Peat and peat substitutes have many disadvantages; they can be too water retentive, holding large quantities of water for long periods. This can lead to the soil mix being continually sodden, particularly during periods of rain in the Autumn, Winter and Spring. Conversely, during periods of high temperatures, dry peat can be difficult to re-wet properly. Organic soils also continue to break down and relatively quickly become compacted and poor-draining. All these factors can lead to root problems and in particular root-rot.
The advantage of inorganic materials is that they hold their open structure for a long time without breaking down into a mush. Inorganic materials retain a certain quantity of water and any excess is immediately flushed through the bottom of the pot; it is difficult to over-water a bonsai planted in a good inorganic soil mix.
There are a number of materials that can be used along with grit when mixing an inorganic soil mix, ranging from volcanic lava to baked/fired clay granules;
Akadama is a white Japanese clay, specifically produced for bonsai; it is normally only available from bonsai nurseries so can be difficult to buy. There are a number of grades of Akadama available including ‘double redline’ that is more costly but is of premium quality. Avoid buying low quality Akadama as it can lose its structure quickly in European and US climates where frequent watering during the Summer is necessary.
Seramis is an orange baked clay, similar to higher-grade Akadama. It is far more easily available in the UK and US where it can be purchased from good garden centres. An advantage of Seramis is that it turns a different shade of orange as it dries allowing an easy indication that it requires watering; the colour is not to everyone’s taste but when top-dressed with grit it is not particularly noticeable. It does however retain its open structure for a long period of time.
Fired clays are excellent soil materials but are costly and can be difficult to locate. They do however hold enormous amounts of water whilst remaining very free-draining.
There are also a number of cheaper soil materials available at most garden centres, they are often sold as soil conditioners. These products can be used instead of baked clays or alternatively they can be mixed with clays to bring down the total cost of the soil mix which is often necessary for re-potting large numbers of trees!
Perlite is a naturally occurring, volcanic rock that is heated to a high temperature. As with baked clays, it is very well structured but also holds large quantities of water. It is also a very light material that makes it useful for reducing the weight of large pots.
Vermiculite is a naturally occurring, mica mineral similar to Perlite. Again, it has excellent water retention and drainage properties. Its advantage over Perlite is that it is a more pleasant colour though Vermiculite tends to contain quite a lot of small particles; around 1/4 of a typical bag can be lost after sifting out fines.
Sifting out ‘Fines’
For a good soil structure that drains well, all soils whether organic or inorganic, must be sifted to remove dust and very small particles. Soil particles smaller than 2mm should always be removed. Dust that remains in the soil mixture clogs the open structure of the soil and disrupts the drainage of excess water.
Switching From Organic to Inorganic Soils
Almost all deciduous varieties will tolerate the transition from organic to inorganic soils as long as they are healthy; coniferous species, in particular Pines, benefit from the retention of some of their old soil which will contain mycorrhiza fungi necessary for growth. If in doubt, make the transition slowly increasing the amount of inorganic material at each re-potting.
The Best Soil Mix for Bonsai
There is no single soil mix that is best for cultivating bonsai; variables such as local climate and rainfall, personal watering regimes and individual tree species all contribute to variations in enthusiasts’ soil mixes. Ultimately, experience of using different soil types and ingredients will shape your own particular preferences. It is recommended that in the first instance, find out the soil-mix of local enthusiasts who have found a successful mix and take it from there. I would however recommend the use of inorganic soils and not organic as they are nearly always of a better quality.
My personal preference when mixing bonsai soil is as follows; (by volume, not weight)
30% Seramis clay granules, 40% Vermiculite and 30% Grit. For additional water retention I increase the volume of Vermiculite at the expense of grit and Seramis, for a very free draining mix the volume of Grit is increased to 50%. My experience of this mix is that even in the height of summer, watering is necessary no more than once or twice a day though excess water is allowed to run straight through drainage holes of the pot. I have yet to experience any drainage or compaction problems, nor have I had any trees suffer with root-rot. Lastly, all these materials are readily available at all good garden-centres at a reasonable cost.