Plant Propagation Basics

LIFE FINDS A WAY
It's really easy to forget that plants are some of the oldest forms of life on the earth. They have survived (and thrived) for so long because just like us they can make more of themselves. Most often you see this in action as something you plant that spreads all over, often quickly. Even in harsh climates plants can adapt through changes in evolution enabled by propagation. No matter what, they will find a way to survive.

No matter what plant we're talking about there are only two types of plant propagation: sexual and asexual. Within those two there are various methods to propagate but in the end, those two are it.


SEXUAL PROPAGATION
Basically, the seeds you buy in the spring are the result of this method. There's a great reference here at OSU's extension and at Wikipedia but here are the basics. Plants that reproduce sexually contain male parts called the stamen and female parts called the pistil. Each one is comprised of several pieces, but essentially the male parts contain the pollen which is carried to the female part where it eventually becomes a seed.

THE WORLD ISN'T PERFECT?
In some plant species flowers can be male or female, these plants/flowers are referred to as "imperfect". Some examples of these are cucumbers, pumpkins and melons. When you plant these types you must plant both males and females near each other. Unfortunately, there is no way to determine the sex of the seed so make sure you plant several. Once the flowers mature you will be able to determine which ones are which and remove extra plants.

Since "imperfect" plants are unable to move around on their own to distribute their pollen the rely on "pollinators" to do the job for them. Sometimes the wind is enough but since it's more unreliable they count on things like bees and butterflies to help out. If you plan on growing species that are imperfect, make sure to plant things that will attract butterflies and bees. You can do it manually with a q-tip, but that's for a future article.

So, the opposite of imperfect are "perfect flowers", these are ones that have both male and female parts on the same flower. Examples of these are tomatoes, peppers, lilies and roses. These don't necessarily require pollinators as a light wind is usually enough. However, I have found that when you have pollinators around vegetables of this type you will end up with a better harvest.

From the plant's perspective, the whole goal of this exercise isn't to produce tomatoes for your award winning sauce, it's simply a matter of the need to survive through seed production. Now, having all this pollen from different plants being moved around opens up the opportunity for genetic material to spread. The result of this can be unusual or completely new plants! Taking pollen from one type of plant and pollinating a different plant is called "hybridizing" or "crossing". This in itself is a massive subject which I'll deal with in a different post.

ASEXUAL PROPAGATION
As I mentioned before there are two basic propagation methods, the second one is asexual. At this point you have probably guessed this is propagation through something *other* than seed. Depending on the type of plant there can be several method of asexual reproduction, the most common are tuberous, bulbous and self-rooting.

Tuberous propagation is where the root system of a plant starts lateral growth from each side of the plant. As these "tubers" move through the soil they send new plant stalks up through the ground. On the surface these tend to look like completely separate plants, however under the ground they're connected. At some point, these connections become severed, either by old age or more commonly by an underground animal. Once severed, each plant is on it's own to start shooting out more tubers to create new plants. These tubers can be dug up prior to the plant going dormant, split into pieces then planted individually the next season.

I'm guessing you have noticed "bulbous propagation" contains the word bulb in it. If you garden even just a little chances are pretty good you have planted bulbs. Things like tulips and hyacinth fall into this class. Bulbous propagation is similar to tubers in that it occurs under the ground. Here however a large bulb is planted and over a succession of seasons small "bulbettes" form in a cluster around the base of the parent bulb. Season after season these baby bulbs grow larger and larger and eventually disconnect from their parent. Once that has occurred, these new parents are free to start forming their own bulbettes and the cycle continues. When the bulbettes are about two thirds mature you can manually split them from the parent in the spring or fall and replant them. This is precisely what professional bulb companies do. They dig the bulbs up, remove and replant the babies then dry and sell the parents to us.

The last asexual method I call "self-rooting" and is my absolute favorite. If you have some ivy around take a close look around where the leaves are attached to the stem of the plant. Chances are good you will see little creamy white "nodules" around that area. Many people mistake these as disease but in fact they are new root systems under development. Get these little roots anywhere near soil and they will almost immediately shoot into the ground. From that point they push out new foliage and stems and the process starts all over again. Commercial growers take cuttings of plants and exploit this propagation method to produce tons of plant material all over the world. It is by far the fastest and most reliable method to propagate many types of plants. I have used this method for years on MANY types of plants, just a few examples are coleus, basil, sweet potato vine, petunias, impatiens, alternanthera and all of the mums I grow come in as rooted cuttings. Details on how to do this will come in a future article, however if you Google for "plant cuttings" you will find tons of results.

GENETIC DIVERSITY
Even this basic introduction on plant propagation requires some introduction to plant genetics. Don't let this scare you off, they are quite similar to us. Every male and female plant flower contains the genetic material to reproduce that plant. During the fertilization process this genetic material is passed to the children of those plants. And, just like humans, there is a ton of genetic diversity which can cause a plant to evolve over time. It is because of this that sexual propagation can, and often does, lead to different plants. If you are a parent of several children you know this for a fact, even though they have the same parents each child is different. Yes, I know there can be twins and such, but this is not the norm. This is a huge subject, enough for books, but the basic thing to take away is this: sexual reproduction (seed) won't always produce the same plant as the parents.

Asexual propagation is the opposite, it's like cloning the parent. In fact, rooted cuttings will be a copy of the parent plant. Well, there can be exceptions referred to as "sports" but that's for another conversation as well. Bulbous and tuberous propagation produce almost carbon copies but the chance for "genetic drift" is slightly higher.

CAN THEY DO BOTH?
As a matter of fact, many plants can be propagated both sexually and asexually. A really good example of this is the coleus. Coleus has perfect flowers (male and female parts) and will produce seed that can be grown into new plants. At the same time, you can take cuttings from it and root them for a copy of it. Why would you choose one over the other? Back to genetic diversity, the chances are pretty good that the seed from that plant won't look like the parent. The cutting will.

Now, in a variety where the genetics have been stabilized it could be just a matter of convenience. Many tomatoes, especially heirlooms, have been around for so many years that the seed are almost always "true". Grow them, save some seed and the next year you have a really good chance they will be the same. However, if you want to push the growing cycle, root a cutting from the parent and you magically get a 6-8 week head start. I do this all the time with many types of plants. We maintain what is called "stock" material for precisely this purpose. I always have the option of starting that plant from seed but many times I can dramatically reduce the growing time, sometimes by half.

MORE TO COME
Hopefully you have a better understanding of the basic of plant propagation. In the future I will address things like genetic drift in more detail and how to avoid it. As always, comments are welcomed!