grafting – The Garden Professors™

The Approach Graft

Seeing as this blog is called “The Garden Professors” it has been far too long since we’ve given you a lecture on a useful practice for your garden, so this week I thought I’d give you a little how-to demonstration on something called approach grafting. Approach grafting is a technique that you could use to graft a tomato to a tomato (good if you want to use a disease resistant root with a non-disease resistant top — common in heirloom tomatoes), a tomato stem to a potato root (just a fun project), or an eggplant root to a tomato shoot (good for wet locations).

So here we go. First, you need two plants that are about the same size, and you need to plant them in the same container as demonstrated below with a potato and tomato. You will also need to strip off lower leaves as they may get in the way of the graft.

Above we have a young potato and tomato plant to be grafted.

In the above picture the potato and tomato plant have been planted in the same container and their lower leaves have been stripped off.

After the two plants are in the same container a small slice is made on each plant at the same height. This slice will be, ideally, just a little bit deeper than the cambium into the center of the stem (you’ll be able to see the plants pith — in the center of the cut — it’s tough to see in the image here).

In the above picture the stem of both the tomato and potato are cut so that they can be joined together.

After making the required cuts on both plants the cuts are pushed together and wrapped. We used parafilm to wrap this graft, but saranwrap, or even an elastic band would also work.

In the above picture the cuts are being joined.

Here the cuts are wrapped.

The next step is to wait until the graft “takes”. This could take 3-5 weeks. After a good strong union is formed the top of the potato and the bottom of the tomato plants are cut off. Wait a few days to make sure everything’s working properly and plant the result in your garden.

A Dangerous Game

Every once in awhile I become infatuated with some idea and can’t stop for looking for information on it. It usually starts when I want to find a good quote for a particular article or column that I’m writing and then ends up swallowing two or three days. Well, it happened to me again yesterday and spilled over into today. I’m currently finishing up a project with an old friend of mine from college who happens to be a political science professor at the University of North Carolina Charlotte. We’re looking at certain environmental issues and the stances taken on them by both the left and the right. Anyway, I wanted to make a point about biotechnology — that point being that when we graft two plants together we often get different chemicals in the plant which we grafted onto the rootstock than we would get if the plant were growing on its own roots. This is because many chemicals can be translocated from the roots to the leaves or even the fruit. Anyway, I quickly found a number of nice scientific articles to back up my statement, but I also found some other fascinating information about, of all things, tomatoes. There are many plants related to tomatoes that tomatoes can be grafted onto. For example, every spring our plant propagation class grafts potato roots to a tomato top. Tomatoes can also be grafted onto eggplant (which is actually very useful because eggplant roots are very resistant to flooding unlike tomato roots).

While the above examples are interesting, they’re also relatively common knowledge among horticulturists. Here’s the part that’s not common knowledge (or perhaps I should say here’s the part that I didn’t know about — I’ve been known to be ignorant of things that other people consider common knowledge before). Tomatoes can be grafted onto tobacco, and, if they are, they will have nicotine translocated to their fruit — not a lot mind you. Most of the nicotine ends up in the leaves and stems of the tomato plant, but still, why couldn’t a nicotine-laden tomato be developed which could help smokers kick the habit — in a semi-healthy kind of way?

I also found that tomatoes could be grafted onto jimson weed. Big mistake there. Jimson weed develops some pretty nasty alkaloids, and they end up in the tomato fruit. So, if you eat the fruit, your done for. In fact, I found an instance where 5 people were killed because they ate tomatoes grafted onto jimson roots. I am now curious about what happens if you graft tomato onto deadly nightshade — but not curious enough to actually try it.

Age

This time of year is very exciting for the students in my plant propagation class because now is when they all get to try grafting. In particular, they get to place buds from an apple tree onto a rootstock. There is nothing like placing a bud from one tree onto another to make a person feel as though they’re a horticulturist (NOT HorticulturALIST — that’s not a real word). Especially if that bud successfully grows on the plant where it was placed and produces a happy new tree — What a warm fuzzy feeling!

There are all kinds of things that a rootstock can offer to the bud placed on it. The rootstock can make the tree a dwarf, it can be resistant to certain diseases which the bud isn’t, it can even add some degree of cold hardiness. In return, the bud produces a cultivar that the grower wants such as ‘Honeycrisp’ apple. Additionally, the bud also offers an older tree. This probably doesn’t make sense at first, so think about it for a second or two. The bud that was grafted onto the rootstock came from a mature tree and so it may be more mature than the rootstock (which may have come from a seed — if the rootstock came from something besides a seed — like cuttings — then the rootstock may also be quite mature). Because the bud from which the top of the tree will grow is more mature than the base the tree will usually come into bearing sooner than if it were grown from seed.

Tree age is a funny thing. Though you wouldn’t expect it, the base of a tree is actually the youngest part of the tree physiologically while the older portion of the tree is at the top from which most new growth comes. The reason for this is that the bottom of the tree was laid down first as the tree first emerged from the soil and so the bud from which that growth came hadn’t had the chance to age much yet. After a few years of growing up the terminal bud developed more and more “age” and so the top of the tree is more mature. Confusing? It confuses me too — and I’m oversimplifying things quite a bit here. Making it even worse, no two tree species seem to age in exactly the same way.

Why I dislike rootgrafted plants

I’m pretty much a live-and-let-live person in terms of plant choices (as long as they’re not invasive). But I’m becoming convinced that oddities grafted onto hardy rootstocks are poor choices, because the rootstock always seems to win. I posted one of these several months ago (see October 28, 2009 ), but just today have just found the poster tree for my anti-rootgraft movement.

A little backstory. I’m currently out at the Washington coast, trying to get some writing and seminars done without disruption. Today I had to make a trip into Aberdeen, the horrors of which will have to wait for another post. Before going back to my retreat, I tried to renew my enthusiasm for life by seeking out bad plants. I was well rewarded.

I have to give my daughter Charlotte credit for spotting these lovelies. There were two of these $50 Betula pendula ‘Youngii’ trees available. I felt like I’d stumbled upon the next winner of “America’s Next Top Model.” I took pictures from every angle, full shots and close-ups, for your viewing enjoyment.

Note that the “unusual deciduous tree with pendulous branches” is a grafted tree, evidenced by the differences in girth at the grafting point. You’ll also note the appearance of vigorous watersprouts emerging from below the graft. (The bamboo stake to the left lost it function years ago, but is still adds an unexpected pop to the overall composition.)

And here she is in her full beauty! The “S” curve of the scion is bisected longitudinally by two watersprouts, forming a giant $! I do have to agree with the tag at this point – it certainly is “an excellent accent or specimen plant” for the Island of Misfit Grafts.

Finally, please enjoy yet a final reason I don’t like grafts:

(Hint: Note the glue glob.)

Graft and corruption

It’s election season – but that’s not why I’m doing a blog on “graft and corruption.” Instead, let me back up and explain that today I gave a seminar on diagnosing urban tree death. One of my points to the group was the importance of knowing the history of a site – what species were selected, how trees were planted, whether there had been any major construction activity, etc. I thought I’d continue the importance of site history into today’s posting.

Here’s a photo of a street tree – a Prunus spp. (Disclaimer: I am not endorsing a candidate for Mayor of Seattle despite the appearance of a campaign sign in the photo.) It’s a healthy enough specimen, though possibly a bit large for this narrow planting strip:

Several years ago you would have seen a different tree in this same spot:

Now did this weeping cultivar somehow transform into an upright form? Let’s look at this second photo in its entirety:

This reminds me of my favorite childhood book on Greek mythology, which had a great drawing of Athena springing from the head of her father, Zeus. Yes indeed, we are seeing the scion of a grafted tree lose the battle to the rootstock. Rootstocks, by their very nature, are vigorous. If we revisit the first photograph again, this time a little closer, we can see all that remains of the poor scion:

Lesson: if you are using a grafted tree in the landscape, you need to keep the rootstock under control. Grafted trees are probably not good choices for low-maintenance landscapes.