Backyard Biotech: Cloning Your Garden

My garden is already ridiculous. I have this problem or compulsion where if I happen to be passing by the organic nursery or, hell, the hardware store, I will stop and buy a six-pack of veggie seedlings, usually some variety of green bean or squash or hot pepper. And just like that, I'll have another row of future produce that will mostly be given away. I just like watching things grow.

It's entirely amazing that all of this structure and, eventually, food can come from just dirt, water, and sunlight. Just a few days after planting, the roots of what was only recently a dried up old seed will have grown into the surrounding soil and the plant and dirt will have become one and the same, in a sense. The edible fruit end result is just an added bonus to the awesome show that is macrobiology.

Seeds and sexual reproduction are cool and all, but one of the best perspectives on garden biology comes via the process of cloning. Nature has been busy cloning itself since the very genesis of biological life billions of years ago, and humans have been doing it for many thousands. Cloning offers not just the guaranteed perfect reproduction of a particular genome, but a short-cut around the process of germination itself, e.g. the procedure by which a living and metabolizing plant emerges from the dormancy of a dry, hard seed. In some cases, this can be accomplished with only the bare minimum of care, as is the case with eager-to-thrive and chemically-optimized tomato plants.

Plants that enthusiastically self-clone in nature include (but are hardly limited to) grasses, onions, potatoes, and strawberries. The process goes like this. First, a "mother" plant grows a certain sort of root known as a runner or stolon. Runners grow at or very near the surface of the soil, radiating outward and eventually forming a bud or node, which is the genesis of a new and genetically identical plant. This node will grow a shoot, which extends above the surface, a process instigated by hormones released by the node's advancing independent root system. In time, the stolon may wither away.

The end result of natural cloning is the formation of a genet, which is essentially a family of clones all living in proximity to the original mother plant. The largest known genet, what some argue is the single largest living organism by mass, is a collection of 47,000 genetically identical aspen trees located in Utah's Wasatch Mountains. Another notable genet, and what is likely to be the oldest living organism on Earth at 100,000 years old, is a stand of a certain variety of seagrass known as Posidonia oceanica that's located off the coast of Ibiza. The Ibiza "monster" measures 8 kilometers across.

When did humans get in on the cloning action? Most sources indicate that it began at least 2,000 years ago with the domestication of olive and pomegranate trees via the distinctly biotechnological process of root grafting. The practice is even described in the New Testament (the book of Romans, FWIW):

The basic idea of grafting, which is widely in use in biotechnology today, is that some shoot or even branch of a particular plant (a "cutting") is attached to the rootstock of another plant. It's basically a shortcut where a new, undeveloped plant is given an old, well-developed root system. This is especially useful for cloning and hybridization, where a plant with some desired trait or potential desired trait can be immediately cultivated with a very high success rate.

Grafting is extremely common in apple cultivation. An orchard may be very old, with a very old and robust root system, but it may be desirable to change the variety of apple being cultivated, either because one sort of apple has become newly popular or, more likely, because there's an entirely new variety of apple on the market, likely the product of one of several Pacific-Northwest and northern Midwest university biotech programs. Washington State University seems to be a particularly prolific creator of new apple varieties.

These new varieties are first patented and then licensed to orchards, who receive not seeds, but cuttings, which are grafted onto existing root stock and in a relatively short amount of time become productive apple trees. (It's beyond the scope of this post, but GMO paranoia enthusiasts should really read up on the thriving world of apple-centered biotechnology.)

As for my own personal biotech lab, I wouldn't have the faintest idea where to start with root grafting. It's possible to buy root-grafted tomato plants, where you get the whole package of old strong roots with a young plant grafted on top, but that's not very sporting for a backyard gardener.

Fortunately, it's pretty easy to make clones without grafting. A cutting from a plant will naturally start to grow on its own given the right conditions. The process is called striking. The basic idea is that some clump of donated tissue (a branch, piece of stem, etc.) can be placed into some just-right medium, likely some compost-mud, soil-mud, or rockwool; it needs to be very wet for the rootless plant-to-be to get the water it needs to develop as a new independent plant.

(For a proper plant cloning how-to, the Suburban Vegetable Gardening blog is complete and concise.)

It may be necessary to add some extra root hormone to get things going and that can be purchased in the usual gardening sorts of places. A word of caution, however: rooting hormone mixtures often contain pesticides and may not be the most organic thing in the world.

So, while there's no end to the list of clone-able plants, some are particularly easy: roses, basil, rosemary, weed, pot, marijuana, peppers, and grapes. In the general case, the procedure is to pick a branch of some healthy plant that hasn't budded or flowered (the hormones at this point are different) and cut it at a 45 degree angle with a sterilized instrument. The angle offers the maximum possible surface area for the future plant to acquire water and nutrients, thus increasing the odds that the cutting will go on to become a successful clone. Many don't make it.

So, given the right medium, you may have a viable plant sometime soon. To really up the viability of your clones, focus on tomatoes. Tomatoes are incredibly easy in this respect and if you've dealt with the plants very much, you're surely already aware that it takes just a small amount of overwatering to force them to start growing roots all over the damn place and not just underground.

It's actually kind of gross.

In any case, I clone my tomatoes by snipping off strong-looking suckers, which are those branches that grow in the "armpit" of other branches. Next, I stick the lower half of the cutting, which should be trimmed of its leaves and subbranches, in a glass of water and forget about it. Nothing else. (Others will advise that the cutting should be placed in some wet soil rather than just water, but whatever.)

There is a failure rate, but the result is often enough a glass full of thin, sort-of translucent roots. When this new root system starts look to not terribly fragile, I take a small pot and fill it half full of good soil and lay it on its side, so the dirt is all collected in one half of the pot. I lay the root-half of the cutting on top of this dirt and, then, I turn the pot upright and gently fill in the other half. This keeps me from having to just stick the new root system in some dirt, though I'm unsure of any actual benefit from this step. Finally, I add a whole bunch of water and maybe five days or so later, the plant will have started to integrate its roots with the soil.

And there it is. In like a week and a half, a new young-adult tomato plant.

I haven't had time to move my latest clones from their pots to the actual garden, and they're just sitting here by the window soaking it in. One is already growing some early tomato fruits, which is not bad for a plant that required no effort or money at all to produce. I'm not in too much of a hurry to get it outside, to be honest: I just like to watch things grow.