Chapter 70 Acer buergerianum
70.1 Trident maple
A classically styled trident maple. The branches have been clipped to produce fine ramification that holds the leaves close together. Larger branches are spaced so the foliage forms well-separated pads. Note the patches of different colors on the trunk. Link to original image
70.2 Soil: General Deciduous / Rich Conifer Mix
Ratio: 3 parts bark, 1 part grit
Add-ins: dolomitic limestone (~5 lbs/yd), Tree-Tone (15 lbs/yd)
pH: ~6.5 (slightly below neutral)
70.3 Moisture
Trident maples like average moisture levels, but can tolerate some dryness.
70.4 Light
Can tolerate low light, but does best in half-day sun to full sun.
70.5 Cultivation Notes
70.5.1 Potting
Trident maples often are my first trees to break buds in early spring. New shoots extend quickly during spring, and unlike Japanese maples, tridents seem to continue growing until daytime temperatures reach the upper 80s or low 90s. A few shoots will keep growing all summer long.
Trident maples tolerate very aggressive root pruning. If roots are pruned just before buds break, trident maple roots can be cut back extremely hard, leaving just a few feeder roots. New roots will sprout very quickly.
Once the new leaves appear, tridents should not be root pruned aggressively. That said, more than once I have cut 50% of the root mass off a well-rooted tree with ample feeder roots that was fully leafed out. As long as I kept them watered and protected from sudden cold or too much sun, all of the trees recovered without problems.
I don’t root prune after the new shoots start their rapid extension growth.
70.5.2 Pruning
Trident maples that have well-established root systems, can tolerate extremely agressive top pruning as well. If a 15-foot tree with a 3-inch diameter trunk (wrist-sized) is cut off 3 inches from the ground in late winter, it usually will have a dozen or more new shoots emerging from the cut end within a month. By mid-summer the longest shoots may be 6 feet or longer. This ability to recover quickly from severe pruning is one of the reasons why trident maples are so popular in bonsai.
Make major branch pruning cut very early in the season to limit the loss of nutrients caused by removing a branch full of tree sap. Branch cuts may bleed for 1-3 days if the sap is already moving up from the roots. There is little need to seal pruning wounds, because trident maple will close over most cut scars that are near flush with the trunk.
Lateral branches emerging from the primary scaffold branches can be pruned all summer.
New green shoots will extend quickly in the early spring. I remove small shoots that are not placed where I want as soon as I see them. I let shoots that I want to build into new branches extend as much as they can until July, then I cut them back to 1-2 pairs of leaves; the buds at the bases of the terminal leaves will provide the next pair of extension shoots, either later in the year or the next spring. Some green shoots turn woody very early in the year, and I often have to switch from scissors to bypass pruners to cut them back.
I expect to hear arguments about this next point, but I have not had much luck with wiring soft extension growth to create lateral branches. Tridents seem to do much better with a grow-clip-regrow-repeat approach. I may be doing something wrong, but wired laterals seem reluctant to thicken further.
Random green shoots will pop out all summer long. Clip them off with scissors at 1-2 pairs of leaves if they are in a place you want to keep them. I stop pruning tridents in early September so I do not encourage late growth that will not be hardened by mid-November (our first hard freeze date).
70.5.3 Feeding
Trident maples grow faster than Japanese maples so can be fertilized more heavily. Fertilize trident maples in spring, after new leaves have begun to emerge.
When feeding a trident maple, use slow-release fertilizers that have about three times more nitrogen than phosphorous. To feed more, don’t go up on the concentration of minerals; increase the frequency of feeding.
Good options:
- Slow release shrub and tree fertilizer, applied at half the recommended rate.
- Organic liquid plant food that must be broken down by soil microbes, such as fish emulsion.
- Inorganic, water soluble fertilizers at half strength rather than full strength.
I have had good luck with feeding trident maple seedlings heavily in spring to encourage their main leader to extend quickly. The growth is soft and falls over in heavy rain but that is not a big problem. I let them extend for 1-2 months then cut the leader back almost completely in mid-summer. This builds a larger trunk and more lateral branches on younger trees.
70.5.4 Pests & Problems
I have had very few problems with trident maples. They can get aphids occasionally but these can be knocked down with insecticidal soap. If sooty mold or other fungus appears, spray with potassium bicarbonate first. Move up the fungicide toxicity scale only if needed.
70.5.5 Winter Storage
Store in mulch outdoors. Try to place in a shaded area so buds do not break in a mid-winter warm spell. Trident maples roots hold a great deal of water, so are susceptible to late freezes. If trees have started to swell for the year and a hard freeze is predicted, cover them during the night with a tarp or frost cloth.
70.6 Propagation Notes
Trident maples grow very easily from seed. Look for a mature tree planted as a street tree. Make sure you are collecting from a trident maple (3 pronged leaves) and not a red maple (5 prongs). Do not be surprised by the size of the leaves. Full size trident maples have much larger leaves. For instance, leaves on the main tree from which I collect my seed are about 5 inches across. Yet my seedlings have leaves from <1 inch to 2 inches across.
Sow the seed in fall in tubs on the surface and barely cover them. Leave the tubs outside in shade all winter. The seeds stratify naturally.
70.7 Artistic & Styling Notes
Trident maples are prone to growing branches with long, straight, uninterrupted runs between branches. These are hard to bend once they are larger than a pencil. Try to correct any straight run branches early.
70.8 Additional Information
70.8.1 Natural History
Trident maples are very popular for bonsai in Japan, but are not native. They come from China, Manchuria, and Korea, and have naturalized in Japan.
70.8.2 In Cultivation
Many unusual trident maple cultivars have been introduced, but they are not easy to find. Most must be ordered online from a specialty supplier here in the US. Importing cultivars directly from Japan is very difficult due to USDA quarantine restrictions on living plants. If you want to import them, plan to spend a lot of money.