The dwarf Japanese Maple “Waterfall” which leafs out beautifully every May in a sunny location for the past 16 years has hardly any leafs on it now on June 4th. The leafs are very slowly and gradually appearing. It doesn’t appear to be diseased. Could this be due to a cold spring and/or too many allium “Purple Sensation” plants which have spread and grown too close to the Japanese maple roots? I am pulling a lot of them out.
Thank you for your question.
Waterfall Japanese Maples are very beautiful. Without a picture, it is hard to provide exact recommendations. Your plan to remove some of your plants that have grown too close in a good idea. The weather has been quite variable this spring and possibly early bud break, followed by a freeze could result in poor leafing out.
As your tree is now 16 years old, current conditions in your garden may be also worth considering. The best soil for Japanese maples is a sandy loam with a low to medium amount of organic matter, well-drained, and well-mulched. Over time, soils may need amending, or sun/shade conditions may change due to your garden maturing.
We get many questions about Japanese Maples and have developed a gardening guide and below is the link to our Gardening Guide on Growing Japanese Maples which will provide you with further details.
While there could be many reasons for the tree not leafing out this year, in addition to the above suggestions, it could be verticillium wilt. While you have not indicated that your branches are dying back, it might be something to consider. Typically branches will be noted to be dying back one by one, often from the tips down. This is because this fungal disease affects the water conducting tissues of the plant and the tips are the furthest the water has to travel.
A previous similar post suggests that according to the Morton Arboretum: https://www.mortonarb.org/
“The fungus lives in soil as small, darkened structures called microsclerotia. These microsclerotia may lie dormant in the soil for years. When the roots of susceptible plants grow close to the microsclerotia, the fungus germinates and infects the roots of the plants through wounds or natural openings. The fungus spreads into the branches through the plant’s vascular system and simultaneously causes the plant cells to “plug” themselves. Once the xylem is infected, it becomes so plugged that water can no longer reach the leaves. Verticillium can also be spread to plants through wounds on branches or trunks.”
This is a tricky disease as it is soil borne where it can live indefinitely. If you are trimming back affected branches, make sure you sterilize your tools afterwards as it can be spread through your tools as well.
I hope you find the above information helpful in determining what is affecting your tree.