Zelkova, aka Japanese Gray Bark Elm, is a wonderful, amazingly vigorous tree species. Zelkova are not elms, but they are in the elm family.
Fast growth in a plant is great for building a bonsai from scratch, but does fast growth become a disadvantage once your bonsai tree is more established? We don't think so! In fact, we like it when our trees grow a lot; that new growth tells us the tree is healthy and gives us a chance to get our Zen trimming practice in.
Managing Vigorous Growth on Zelkova
If your Zelkova already has a lot of branches and is growing nicely in spring, pinch half the tips; the ones that are extending the most. Then wait a couple weeks and pinch any other tips that extend past the edges you already created in your canopy. "Pinching" is the act of removing the fresh growing tip before it extends very far; you can pinch with your fingers, or use scissors. If you continue getting more growth in the summer, just use the same process again.
A common situation for a bonsai tree is that it has branches that are dense enough so that the upper ones shade the lower ones. In this situation, defoliation - removing the foliage - is one way to improve the amount of light that reaches the interior of the tree. You can remove all the leaves, or you can just remove all the outer leaves, or the upper half etc. With Zelkova that are growing vigorously it's a common technique to remove all the leaves. Simply pull them off with your fingers, but be a bit careful if the branches you're working on are very tiny and green - you might pull off the whole branch. If you prefer you can use a pair of scissors to cut off the leaves, it just takes longer to do it this way. If your tree isn't growing quickly, don't remove all the leaves. You should also hold on removing leaves after about mid-August in most places to give the tree enough time to grow more leaves before it starts to go dormant in September or October.
If you forgot to pinch your tree and you now have some shoots, then you'll need to remove them using scissors. You can cut all the way back to the first or second leaf near the base of the shoot. The leaves at the base are normally smaller than the ones further out, and cutting back this way makes the tree make more branches close to the trunk. Use a pair of scissors that have a small point, not a pair of garden shears or kitchen scissors.
Tweezers are also useful for working on Zelkova, especially mini-bonsai since they commonly have branches that are very close together. Use the tweezers to pull off the leaves.
Whenever you remove all the leaves from the tree, or if you wait until they fall off as the temperature drops in fall, you should trim back all the little twigs to create a nice shape and to remove any that are too large, crossing each other, or growing in crazy directions. It's common that the first couple nodes (the spaces between where the leaves are attached) are shorter and more useful for bonsai than the nodes that are further out on new branches.
Making Bigger Cuts to Remove Large Branches
If you didn't stay on top of cutting back the shoots on your tree, and it's been vigorous and happy, you may have to make larger cuts to remove branching that has become too large. Zelkova have a habit of making a large callus around wounds, so trimming regularly can avoid problems. If you have to make a larger cut, try wrapping the edge of the cut with grafting tape, raffia or other similar items so that as the wound heals it does not swell outward.
Encouraging Growth in Zelkova
While they generally produce new growth quickly, Zelkova have also been known to sulk, sitting in place and sending out only one set of shoots each year.
To encourage faster growth during spring, summer, and fall, use regular fertilizer and try to arrange to place the tree in a warm temperature and high humidity setting. Absent one or more of these factors, try to position your tree in different places in your growing space to see if this helps the growth.
If your tree is still growing slowly, consider double-potting it; nestle the bonsai container into a larger container of soil and let the roots run out the bottom. Cut them off every month or two. Be sure to fertilize the smaller container and water it properly so that the tree continues to rely on those roots.
Managing Branch Junctions
Zelkova are prolific at budding off existing wood, and as such, you can find yourself with many shoots coming from one place. Regularly use tweezers and scissors to remove shoots that are emerging at sites where there are already two branches. Encourage buds that come from places with no other growth while promptly removing those that are redundant.
Diagnosing Health Problems in Zelkova
Leaf burn on Zelkova is common, and can be the result of a few different things.
- Poor water quality
- Low humidity in combination with hot temperatures
- Cold summer temperatures and dry conditions
- Poor root health
- Fungal pathogens
Nutrient deficiencies in Zelkova can also cause your plant to stop growing nicely. If your leaves are pale green or yellow with darker veins, you may have nutrient deficiency. Try adding more fertilizer!
Scale insects on Zelkova are not widespread, but can occur. Since scale insects suck sap from the tree, they can slow the growth and even cause branch dieback. If you find scale on Zelkova, spray with a soap spray once, then again two weeks later and a third time two weeks after that. You can scrape the bugs off with your fingers or a toothbrush. Systemic chemical insecticide can also be effective, but if you have just one tree it's actually faster to just physically remove them! (rather than getting the chemical, mixing it, spraying it etc...)
Seasonal Changes in Zelkova
In spring, your Zelkova bonsai should send out new leaves and shoots from all of its branches. They can leaf-out as late as May in mild climates.
In summer, Zelkova should have dark green mature leaves, and light green new leaves. Full or partial-defoliation as discussed above can provide finer branching and better light penetration to lower branches.
In fall, you should expect that Zelkova leaves will change color and fall off. This can also happen if the temperature drops suddenly, like when they are moved from a hot greenhouse to outside. The fall color on Zelkova can be bright yellow, orange, or red, depending on the tree's genetics and the fall temperatures among other conditions.
In winter, Zelkova are hardy trees; well-crafted trees provide dense fine twigs and beautiful smooth grey bark.
Is my Zelkova dying or going dormant?
In summer and fall it can be hard to tell if a tree is dying or just going dormant. Zelkova leaves should turn color before they fall off in autumn. If leaves brown completely and stay on the tree, this may be a bad sign! However, we have seen Zelkova leaves brown and fall off and had the trees leaf out the next spring with no problems. If you just acquired the tree, some adjustment to your micro-climate and watering routine may cause problems that make a Zelkova go dormant.
If your tree does lose all its leaves, keep it safe and secure through the winter and watch carefully in spring. Hopefully you'll get a happy flush of new growth!
Planning for the marathon
Bonsai is a marathon, not a sprint. If you use the right techniques over and over, you'll be rewarded with amazing results. Zelkova can get really big trunks, or the trunks can stay small and elegant. Your long-term plan for what you want your tree to be is the most important part of growing. Each time you work on your tree, keep your vision for what you are trying to accomplish in mind. Ask yourself each time, "will this make my tree more beautiful and bring me closer to my goals with this tree?"
Want inspiration for your Zelkova? Keep an eye on our Instagram feeds @bonsaifyonline and @ericschraderbonsai, and on the Bonsaify YouTube Channel.