How to deal with understock if it grows back
Like the Ford Pinto's appearance on the car scene, understock should not reappear on your grafted trees. When it does, it is easy to deal with and can encourage much healthier growth. When we ship trees out we try and trim the understock off but sometimes months, or years down the road it will make a comeback. When this happens all you need to do to fix the issue is carefully inspect the graft junction and trim off the understock with a pair of clippers.
1975 Ford Pinto
Understock on an alpine fir
Glacier alpine fir (Abies lasciocarpa 'Glacier')
This time of year, understock has a tendency to regrow from just below the graft junction.
See how on this fir the foliage on the lower portion is a dark green color, indicating that it may be the understock instead of ‘Glacier’. Some varieties are much more difficult to identify without careful inspection of the lines of the graft junction. If you have questions about where to trim, feel free to send us some photos in an email, and we can help walk you through the steps.
Black Princess Japanese Maple (Acer palmatum 'Kuro hime')
Sometimes it is difficult to identify the understock on some grafted maples. The foliage can be almost indistinguishable with other green-leaf varieties.
Here ‘Kuro hime’ is pictured, having slightly smaller leaves and a more globose habit, indicating that the shoot emerging on the bottom left is not part of the grafted plant but actually understock reappearing.
Snow Cloud Ginkgo (Ginkgo biloba 'Snow Cloud')
This is an easy one! Clearly the ‘Snow Cloud’ ginkgo has the creamy-yellow leaves, and the understock is the dark green portion.
Notice how the close-up photo shows that the understock is regrowing from more than one place. Using a pair of thin-tipped pruners, these sprouts can be cut back close to the trunk to discourage reemergence throughout the growing season.
Peve Minaret Bald Cypress (Taxodium distichum 'Peve Minaret')
Just like we saw on ‘Snow Cloud’, the understock is coming back from more than one place on this ‘Peve Minaret’. It has many sprouts of understock shooting up from the base!
It is important to be especially observant of the understock on Taxodium (Bald Cypress) and Metasequoia (Dawn Redwood) because they have a tendency to grow very rapidly, overtaking the graft relatively quickly if left unchecked.
All of this information can be disparaging, but fear not: if you remove the understock before it becomes too vigorous, it is no cause for concern and is normal to happen occasionally on young plants.
However, do be vigilant because, if left unchecked, the understock can grow enough over time to take over the grafted plant. Careful identification of what to prune is also important. As you can see from this photo, the Picea abies ‘Cupressina’ (on the right) looked very similar to the species Picea abies (Norway Spruce) understock used which is the only thing remaining of the tree on the left! We hope you now have a better understanding of how to help your plants get established.