propagation – The Garden Professors™

Propagating in the air

Most gardeners that I know have tried to produce roots on stem cuttings from plants that they like. Sometimes this turns out well for them, particularly if they are working with what we call an easy-to-root species, and sometimes it turns out poorly. OK, in all honesty, it often turns out poorly. The problem is that plants like very particular conditions when they’re growing roots and the typical gardener is going to have a tough time providing these conditions. So here’s an option. There is a method of propagation called air-layering which works on many plants that stem cuttings won’t work on and which doesn’t need all of the specialized equipment either. It’s not a sure-fire technique, but it’s more likely that the average gardener will get this technique to work than any other (with the exception of seeds).

Here’s how it works. Select a small branch from the plant you want to propagate. Find a point on the branch about 6 to 12 inches from its apex and then cut out a ring of bark around the circumference of the tree. This will allow water and nutrients to flow into the branch (assuming you didn’t cut too deep), but it won’t allow the carbohydrates produced in the branch to flow down the stem — instead they’ll be stuck where you made your cut and be used by the plant to produce new roots.

Around the cut you may apply a rooting hormone. This will help the root production to some degree. To keep the wound moist apply a heaping helping of moist peat and keep it in place with plastic wrap — or a cut up sandwich bag. Wire ties, elastic bands or string will hold these in place. Now you just sit back and wait.

It usually takes anywhere from 4-8 weeks for roots to emerge (you’ll see them when they do because they’ll push up against the plastic wrap). Once the roots are there plant your new tree/shrub/perennial in it’s own container just like you would any new plant, care for it as you would any other plant, and then plant it out if you so choose (I like to keep young plants like this in a container for at least a few months — the landscape is usually a harsher environment than a container, and so the time in the container gives it a chance to get stronger and store needed nutrient reserves.)

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.

Is It Worth Anything?

Plant aficionados everywhere are constantly looking for something which they can patent and make a million bucks on — something like ‘Endless Summer’ hydrangea which captured the public’s attention — and their wallets. Many of the new plants we see today came from something called “branch sports” which are basically segments of a tree — like a branch — which has somehow mutated so that it offers something a little different than what the original tree did. If you’re familiar with ‘Delicious’ apples you may be interested to know that the ‘Delicious’ apples which you eat today are actually a branch sport of another ‘Delicious’ apple which wasn’t as attractive. Likewise, ‘Connell Red’ is actually a branch sport of ‘Fireside’ — they’re basically the same, but ‘Connell Red’ is considered more aesthetically attractive.

But some of those mutations are heart-breakers, Here’s an example.

This raspberry, which I found in my daughter’s raspberry dish last night (she was very upset that I stole it) has a really cool stripe running down it’s side. If someone found this in a raspberry patch they might be tempted to try to propagate the branch from which it came hoping to get striped fruit. Unfortunately that isn’t likely. This is an example of a sectorial chimera — where just a strip of tissue has been mutated. These types of mutations are notoriously difficult to propagate and so it’s unlikely that this mutation will last after propagating the branch from which this raspberry came. Still, it is kind of cool, isn’t it?

The Heartbreak of Plagiotropism…

…Otherwise known as “splayage”. When vegetatively propagating some species of woody plants, care should be taken when selecting where to take a cutting (piece of stem) to root. Propagation from terminal cuttings (pointy end up) usually results in orthotropism or a vertical growth habit. Cuttings from extremely lateral branches (those that grow parallel to the ground) can, in a few species, result in a spreading growth habit or plagiotropism.

This is not always undesirable – some species are purposefully propagated this way to maintain the prostrate habit that particular cultivar is known for. I’ve propagated lots of Buddleia over the years and don’t recall having this happen. Jeff, you were “Mr. Buddleia”* back in our days at UGA…please weigh in on this!

Floppulence
Buddleia davidii ‘Santana’, author’s garden.

Said plant was purchased from a little Mom & Pop greenhouse as a 4.5” pot with a 6” tall rooted cutting, and it went into our garden in May. It is now lolling all over its neighbors like a drunken sailor. What looks like a vertical piece in the back is simply propped up by the Canna. No big deal, just a good teaching moment.

‘Santana’ is a bit slower-growing than most cultivars of Buddleia, yet is in great demand due to the wacky variegated foliage. My guess? This is the result of repeated acts of propagation via lateral branches…cuttings of cuttings of cuttings. Not to mention the fact that it’s patented, so this guy may not only be floppy, but illegal (!). One of the purported upsides of the plant patenting process is to control the quantity and quality of propagation through licensing. But that’s another post topic for the future.

*Not to be mistaken for the pageant winner “Miss Buddleia”