Hey everyone,
I have an area surrounded by pavers that currently has a pyramidal european hornbeam in it. Its 5b zone, very compact clay soil, minimal topsoil due to the pea gravel for the pavers and everything seems to now drain into this hole. I’m pretty sure I’m drowning this thing.
1) is there anything I can do to save it without moving it?
2) what tree would grow in this compact clay & standing water location?
Thanks!
Aaron
Thank you for contacting Toronto Master Gardeners about your Pyramidal European Hornbeam. Carpinus betulus ‘fastigiata’ is a member of the birch family, and is not native to North America. Attaining a height of 30–40 feet and a spread of 20–30 feet, this tree is hardy to zone 4 (although experts differ on this point). This tree does best in full sun- to part shade in average to moist soil conditions- it shouldn’t be allowed to dry out.
The tree has no serious insect or disease problems, generally requires low maintenance, and needs little pruning except when necessary to remove dieback, for example. The cultivar ‘fastigiata’ refers to the erect, almost parallel, growth of its branches producing the pyramidal form that works for many urban gardens. It has many uses in the garden including an accent tree, shade, and as a hedge or screen. With age, its form gradually acquires a tear drop or oval-vase shape.
One difference between our native hornbeam, Carpinus caroliniana, and its cousin, the European hornbeam, Carpinus betulus, is their tolerance of drought. The European hornbeam that you have prefers average to moist conditions in either loamy or light clay soil, and it is only moderately drought tolerant. The native tree prefers abundant soil moisture and commonly grows along the borders of streams and swamps as far south as Florida. The European species is larger at maturity than our native species and although it can grow in partial shade, it likes full sun. The native species would be a better choice in the planting situation that you describe. But since very few trees of any species can tolerate compaction by paving stones and persistent flooding of its roots, we need to deal with these problems.
You don’t mention any other symptoms of “drowning,” but that information would help to determine a course of action. The pea gravel and pavers are directing the path runoff water to the base of the tree, but does the water drain into the soil or stand on the surface for some time? If the tree was planted in a good quality planting soil mix it should drain freely. If this is not occurring then it is likely that the soil is compacted and or a heavy clay. These conditions are not conducive for healthy tree growth, even without the water issue.
Without good drainage your soil needs amending, but the technique depends on the level of stress your tree is under. Although it would be best to see a photograph of the tree and planting site, it is clear that to improve the likelihood that your tree will adapt and thrive, it is necessary to remove the impediments that it currently endures.
If your hornbeam is in full leaf but not shooting new growth, you should remove any pea gravel around the base of the tree and replace it with 2 inches of organic compost to a diameter of 4 ft. Add a 2-3 inch layer of natural mulch on top of the compost. Avoid contact with the trunk, as the compost and mulch will retain moisture and could encourage disease growth if it is in contact with the trunk.
If your tree is seriously declining, with die back of branches and leaves, your soil amendment needs to be more substantial. Depending on the size of the garden bed surrounded by pavers, you can dig out the top 18 inches of compacted soil around the tree- or for the entire bed if it is small. Avoid the trees roots, by starting your dig about 6 inches away from the root ball. If your tree was planted within the last few years, this will be easy to identify.
Aerate the soil at the base of your hole with a garden fork, avoiding tree roots. Mix about half of the excavated soil in a wheel barrow with organic compost, then return it to your bed. You will end up with excess soil to relocate elsewhere on your property. Add a 2-3 inch layer of natural wood mulch over the bed. The finer shredded mulches, such as natural cedar mulch, break down more quickly than pine bark chunks, releasing nutrients into the soil. Once the mulch has decomposed, you can top it up. This takes a few years.
This solution does mean an expenditure of considerable time and effort, but if you measure the long-term advantages of a healthy tree against the disadvantages of eliminating the gravel, any pavers too close to the tree and compacted soil, you will enjoy the benefits of conserving your pyramidal American hornbeam for years to come. The ‘fastigiate’ cultivar that you have can live up to 120 years given the right conditions, surely a heritage worth supporting.
There are relatively few trees, and few plants in general, that thrive in standing water. We recommend that you keep the pyramidal European hornbeam where it is. Instead of changing the plant, it would be best to change the situation to which any plant at that location would be subjected.
For more information about the pyramidal American hornbeam, please see these links:
http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=a344
https://piedmontmastergardeners.org/article/consider-a-hornbeam/
https://www.uaex.edu/yard-garden/resource-library/plant-week/fastigiate-european-hornbean.aspx