Topworking pear can effectively remove invasive hawthorn (Crataegus monogyna) trees by replacing all seed-bearing limbs. A side benefit is edible pears.
It seems whenever I would teach a grafting class, some young guy would pipe up and say, “I read you can graft pear onto hawthorn. Is it true?”
All I could answer was, “I don’t know. Lets give it a try!”
But it was easier said that done. For all the ubiquity of weedy hawthorn trees through the Northwest, it took years to find some I could try grafting onto. I certainly did not want to plant any more of these thorny trees for the experiment. There are far too many of them already.
Finally, last spring I got to know a property owner whose land was infested by hawthorn trees, and he welcomed me to give it a go.
During the period of April 17 to April 28, I topworked several hawthorn trees.
I sawed them off and bark-grafted them to pear.
I used the standard technique of my video.
By July a lot of them had grown out abundantly.
But not all. This is why.
Deer were standing by, curious what this human had been up to.
The long term outcome of grafting goes far beyond the compatibility of scion on stock. The main reason to graft pear onto hawthorn is to “eliminate” weedy hawthorn trees.
It may not be evident how topworking does this. You might argue, the major part of the hawthorn tree is still there. Well, the tree itself is not invasive. It is rooted in one spot, and can’t move.
What’s invasive are the seeds. Left to itself, a hawthorn tree blooms every year, and makes thousands of small red berries. These get spread around, and new sprouts come up.
After a hawthorn tree is topworked to pear, it does not bloom hawthorn flowers any more. The blossoms are pear, as showy white in springtime as the thorn flowers used to be.
The fruit, instead of hawthorn berries, is now pears. Even if nobody eats them, there are no more hawthorn seeds from that tree. Even if the pear crop fails.
What’s more, people are now interested in that tree. They come to it for fruit in the fall. Where it was once a thorny part of the landscape, nondescript except for a few bloom weeks in the spring, now it’s a focal point.
Years later, even if people don’t understand what it is, they will know “that pear tree”. They will be invested in the care of the land, and the area.
If they do understand what it is, they will support the same work on more hawthorn trees, thus curbing the spread of this invasive.
Deer are browsers. They want to eat tender new growth. This is exactly what fruit tree grafts are, in the critical stage going from the dormant scions you put in place, to the replacement limbs you want them to become.
Most hawthorn trees that are candidates for topworking are in open land, exposed to deer.
Deer browse to a height which is approximately shoulder-level on a human, depending how tall you are and how desperately hungry are the deer.
The easiest height to topwork trees is, unfortunately, a smorgasbord for deer.
Why not graft higher?
First, take note that the grafted-on parts are going to grow upward. There will be very little fruit at or below the level where you graft. Practically all will be above. To eventually reach the fruit, you want to graft as low as possible.
It may not be obvious until you try it, but grafting at or above eye level is a big step up in difficulty.
You cannot easily move around to all sides of the work, to clearly see what you are doing. You need a ladder, or at least a stump, to stand on. This is immediately problematic, especially on uneven ground. The fruit that eventually appears will be all that much further up in the sky.
This first try of grafting pear on hawthorn has been a demo in many ways.
Whether or not the grafts themselves were compatible, I knew deer would be a problem. I intentionally did some grafts where I thought deer would eat them. Sure enough, the deer did.
The test case was a hawthorn tree that was originally leaning across a path. Once cut, the end was right by the path, and low down.
Shortly after doing this doomed graft, I had a friend stand there for scale. You can see the grafted trunk is well below shoulder height.
Deer can be dainty eaters. They nip off the tender shoots, but have less interest in the woody scions themselves. Below is a picture of a scion gamely trying to re-grow after being browsed.
The clue that there used to be a healthy shoot on top is the full-sized leaf below. Top buds grow first, but all that remains is a stub.
To the casual glance, it may look like a grafts never “took”, or barely did.
Sometimes browse is evident, as bitten-off twigs.
After a couple cycles of this, the grafts die. The stock tree itself may die, or at least be strongly set back, because it is depending on the new leaves from the grafts for photosynthesis.
It’s important to distinguish whether a graft was incompatible, that is something inherently wrong with it. Or if the graft itself was fine, but got eaten.
In my test case, the proof is the chomp marks. Here, the deer were so enthusiastic, they bit into the woody scions themselves.
Is topworking in open land futile?
This demo was a test of many things, including deer browse deterrence.
Of the various things I tried, the one that worked best was piling brush around the trees. This was the thorny branches left over from preparing the trees.
I piled brush waist high, chest high if there was enough, to completely surround the trunks. I could not have got to the trees afterwards myself. I’m sure the deer could have got through if they really wanted to, but they moved on to easier pickings.
There are many questions still to answer.
I tried first bark grafting because it is the appropriate technique on large-trunked trees. But there could be better methods.
In summer, I found some small shoots the right size for bud grafting, and tried some of those.
By now, they look well healed.
Some even sprouted during the summer growing season. This usually indicates good compatibility.
All the pear varieties I tried did grow well, if not browsed. But there are hundreds of kinds of pear. It could be that some are graft-compatible on hawthorn and others are not, as on some quince rootstocks widely used for pear.
It’s not yet clear whether grafting on hawthorn dwarfs pear, which would be desirable.
Hawthorn trees seldom appear to suffer drought stress in our dry Northwest summers, so it could be they will support pear without irrigation. Or the opposite might be true, and the grafts will fail, or lose their crop, under drought.
There might be some long-term delayed incompatibility, as in grafting pears onto apples.
To get answers, I would be interested to try grafting pears onto hawthorn at other sites. If you have a place to try, please get in touch.