Good quality bonsai soil is not cheap. Recently there have been large increases in the price of imported substrates such as Akadama, pumice, lava rock etc. Some stockists are quoting a threefold price increase due to post Brexit duty payments and other additional costs. It is all the more important to recycle your existing soils rather than throwing it away. I know that many people already recycle their bonsai soil although I don’t know the process they use to do it. I thought that I would share the process that I use in the hope others comment or share their processes.
Some bonsai substrates will recycle better than others. For example Akadama is excellent at absorbing moisture but has relatively soft particles that break down into dust eventually. Whereas pumice is harder and doesn’t break down as easily. Therefore it can be recycled more times. I use a mix of different substrates for my trees depending upon the type of trees. A general mix that I use is equal parts of Akadama, Pumice and calcined clay. The size of the particles is usually 3-5 millimetres.
When repotting my trees I check the condition of the soil particles to see if they have broken down to dust or if they are still mainly in tact. If it looks like it is suitable for recycling I first of all carefully remove all weeds and moss from the surface. I then rake the soil particles from the tree roots into a container and leave it to fully dry out. This process goes on over the spring period and depending on how many trees I repot I usually end up with several containers full of old soil. I find the ideal time to wash, sieve and clean the soil is nearly a year later in early spring, just before repotting gets underway.
Firstly I put several scoops full of old soil into a sieve with a fine gauze fitted. Sieving the mix initially gets rid of the fine dust but also causes the old roots and vegetive matter to clump together so it can be picked out. I will agitate the sieve several times and pick out as much dead root matter as I can. For the next stage I use a fine watering rose to rinse the soil in the sieve as this washes through any trapped dust particles.
Next I empty the soil into a container and fill it with water. This causes any bits of dead root or vegetation to float off and be discarded. Repeating the rinsing whilst agitating the soil eventually clears the water and cleanses the soil.
After draining off the water I then sieve using a larger mesh so that the soil is the size that I require – usually 3-5 mm. Next the sieved soil is put into a clean container, (I use an old plastic sweet tub as there’s usually lots about after Christmas). Then I ‘cook’ the soil for at least five minutes using an old microwave that I have in my garage. This is to kill any bugs or weed seeds in with the particulate and also helps to dry it out. Once the particulate soil is dry and cool it can be used on its own to repot trees or mixed with new bonsai mix soil. Although this can take up quite a bit of time to complete it does provide me with additional bonsai soil for repotting, saves a precious resource from being wasted and saves money.