For people who are just starting with bonsai, one important question is where to get good material. The often-heard recommendation is to go to a bonsai dealer or a small-scale plant nursery. Of course, these are places to get good trees. But for more mature material backyards are often very good sources. These are not yamadori, but the term yardadori is getting more and more traction.
As an example, this hibiscus dug up in early May (which is a little late in the year, to be honest).
Where do you find bonsai material in gardens?
Normally you would not just walk into a garden and start digging. I have had some success ringing the doorbell and asking for permission to replace an old overgrown shrub in a yard. Often people would like to get rid of them but do not want to spend the energy digging them up. But there is another way which I use more frequently.
I typically monitor private trading websites (such as ebay, freecycle, craigslist). Often a few days before the weekend or right afterwards there are offers of free or cheap garden material. Often these plants require a pickup directly or within a few days, which means there is no option to dig the plants at the optimal time of year. As such I normally only monitor in spring or early fall and I only check advertisements within easy driving distance. After all, a picture is a bad example and I do go to people to take a look. If I like the plant, I dig it and take it. But at times I leave things in the garden too. So for the Hibiscus of this thread the owner had 7 of them in the yard. That weekend they had to be dug. I took a look and decided two of them had some bonsai potential.
What makes interesting bonsai material?
Of course, it is important to understand what a bonsai is. Besides that, I always look for large shrubby plants. As a rule of thumb, each metre of branch length will create a thickness of about 1cm. So, finding a plant with several branches of multiple metres long promises a decent trunk. If you take shrubs with a few very low branches, chances are that you can trim these away and create a nicely tapered trunk. Of course, look for species that take well to transplanting and are generally considered good for bonsai: Consider Azalea, Yew, Privet, Lonicera or hornbeam
How to collect a shrub for bonsai
It is important to prepare a few things before you set off. Ensure you have sufficient substrate and a range of pot sizes. Or a stack of wood so you can build a fitting grow box. Every time I am surprised how wrong you can be with size assessments. It is important to pot the plants as soon after digging as possible.
Subsequently go and take a look at the plant. Do realize that the owners typically would like to avoid a mess in the garden. Sometimes they think it is a waste to trim back an old and large shrub. As such I always explain what my plan is, and ensure that any payment is made before I start. At that point it is after all your risk whether the actions are too drastic. Then you verify were the roots are, which is not always clear. Most of the time you have several main roots around the trunk.
With large caliper branch loppers, I trim the shrub to a more manageable size. Here I on purpose do not cut back to the final size, or even the size I want for recovery. With longer branches any buds and branches on critical places are better protected during transport. With a sharp spade cut a circle around the trunk between 10 and 30 cm away from the trunk (Larger plants large, small shrubs, closer). Normally this will give you enough of a root ball to make a successful transfer with a root ball you can lift and repot. On one side of the tree the soil outside the circle is removed, allowing to undercut the root ball. (Of course, if you are in rocky soil or clay it may be more work than explained here; I am lucky to have soft sandy soils). When lifting the tree remember that soft sandy soil easily drops from the roots. So, ensure the soil is moist and keep bags or cloth nearby to wrap the root ball. Keeping this together for as long as possible will protect the roots. If the substrate drops of, wet the roots and wrap in plastic foil. Time to go home!
At home clean out the soil with a root hook. Gently but swiftly remove the soil. Do not allow the roots to dry out. Work in the shade out of winds and spray with water if needed. After cleaning out the soil you can see where the optimal nebari would be. Often you have more than one level of roots due to improper planting. And for pot-grown plants which have been planted out often the shape of the pot is still visible in the roots. Choose the nebari line based on the smallest cuts needed, and avoid inverse taper, keeping in mind the final design of your tree.
In this case, I decided to remove the top roots and use the original nebari as this gives the best swell. Trim the roots back as far as possible. This typically is back to the first branching of the root, leaving the smaller branch and trimming the main root. As visible on the picture: We had 6 weeks of no rain and then a few small rainstorms. All main roots responded to the availability of surface moisture and made many small side roots. This will greatly help the recovery of the hibiscus.
Now it is also possible to judge the size of the final tree and cut the branches back to a rough outline. I always keep them longer than needed allowing for some die-back during recover. As such, I will also not make any cuts flush with the trunk. This can always be done once roots have recovered and top growth has started.
Potting and aftercare
Time to plant the new tree. Put a layer of substrate in the pot. Wiggle the tree in place and tie the tree down in the pot. If the roots are sparse or weak, tie it to the branches. Fixing the plant properly helps recover and reduces the risk of the tree being blown out of the pot during the establishment period. Ensure that the nebari is covered with a few cm of substrate. This will help the development of new roots. Make sure the root ball is smaller than the pot you will use for recovery.
For substrate I used coarse bims, mixed with ground up bark. This is a well aerated substrate allowing for good oxygen exchange and high moisture without the risk of suffocating the roots.
Plants like these I put in the shade for some 2, 3 weeks. During this time the tree will use its reserves to grown new roots and start pushing buds. As deciduous trees have large reserves, direct sun is not needed at this stage and less pressure is put on the roots as no water is needed for evaporation in the sun. Coniferous species typically have less reserves and normally need to return to the sun fairly quickly after.
These trees will be fertilized whenever my other trees are fertilized which is about a week after collecting.