One thing that fascinates just about every plant lover is the process of propagation, and finding easy ways to make more houseplants, vegetables, and flowers from those plants you already have and love. If you’ve ever tried to propagate a plant, did you know your success rate was just as dependent on the type of plant as on your abilities? There is much more to plant propagation than most people are aware.
Once you realize that every stem or leaf petiole is a growth opportunity, you’ll begin to see your plants in an entirely new light. Unfortunately, learning the propagation ropes can be challenging. Enter the new book, Plant Parenting from this week’s guest, Leslie Halleck.
Like it or not, a little botanical science really is necessary to help you understand the fundamentals of plant propagation. Fortunately, Leslie’s book provides that foundation in an easy-to-digest guide to propagating both indoor and outdoor plants.
Plants can be reproduced in many different ways – from seed to stem cutting to leaf section to a trunk or stem wound. The manner in which some plants reproduce can be unexpected and fascinating. More on that in a minute.
Let’s start with the flower. The flowers of a plant species can be either “perfect” or “incomplete.”
A perfect flower contains both male and female parts. It can pollinate without the need of any other flowers. An incomplete flower is either male or female. Incomplete flowers require pollination between their flower counterpart – joining male and female. Not only that, but some species – like ginkgo – have male plants and female plants.
Since – for all flowering plants – the male and female parts must interact, understanding what you’re dealing with will help you to achieve a goal of generating fruit and seed from your plant.
The seed your plant produces may not grow into the plant you expect either. For example, a seed which is the result of cross-pollination between two varieties can produce an entirely different plant – one with mixed qualities of both parents.
This is the case for cultivated hybrid plants. Hybrids are the result of intentionally cross-pollinating two varieties – two different types of tomato, for example. (I’m a tomato fan, so I love to use tomato examples.) The cross-pollinated fruit produces a seed which will develop into a plant with traits of both parent plants.
However, the traits which come through in that first generation plant are unique to only that generation. The seeds which come from the fruit of that first-generation won’t produce a second-generation plant with identical characteristics. The newly-blended genetics from the hybrid are too unstable to carry into future generations.
If your plant is an open-pollinated variety (such as heirloom tomatoes), on the other hand, the genetics within its seed have stabilized through generations and, so, will produce a plant with the true characteristics of its heirloom parent – a true seed.
So what if you want to create more of a plant which doesn’t produce true seed? Well, there are a number of vegetative propagation methods.
I love Sungold tomatoes. They are a cultivated hybrid variety. I can’t save and grow the seeds, because they won’t reproduce the Sungold tomato. Instead, I use suckers or cuttings from a first-generation plant grown from purchased hybrid seed. These plant parts will create a Sungold plant clone.
The vegetative growth is often your only option for propagation, but it’s important to understand that plant parts can be genetically hard-wired to react differently than you might anticipate. It all depends on the totipotency within the species’ cell structure.
Totipotency is the ability of a single cell to divide and produce all of the differentiated cells in a plant. In some plants, stem tissue can be triggered to produce root growth, rather than foliage.
That Sungold tomato is a great example. While the tissue of its stems and suckers are vigorous to produce more stems and foliage, they are just itching to create roots too. Not all plant species contain tissue so eager to shift gears.
The stems of some species will only produce new roots at the point at which a leaf nodule is located. Separating the stem from just below the nodule will trigger the nodule cells to grow root tissue rather than foliage.
These methods work for most fleshy, herbaceous plants; and oftentimes, all that’s necessary for root development is a container of water or moist soil to keep the cut from drying out. However, some plant stems – particularly those of woody plants, like hydrangea – are a bit trickier.
A cutting must be kept moist in order for roots to develop, meanwhile that moisture can also foster rot. So, propagation through cuttings become a race between rooting and rotting.
If you’ve ever rooted a plant from a cutting, have you ever wondered where the roots actually come from? That’s where a little more basic botany comes in.
Hormones within plant cells help to dictate the structure of the plant as it grows. New leaves? Woody stems? Roots or flowers? These developments are all tied, in part, to hormones.
IBA, a type of “rooting hormone,” is a synthetic version of the hormone which stimulates plant root growth. It can really elevate your game, when it comes to propagation.
Rooting hormone is readily-available in a liquid, gel or powder form and should be applied to the open wound of a cutting to speed up the plant’s natural ability to generate roots. The hormone should be applied immediately after the cut – before you place it into soil or a container of water.
I use rooting hormone often when propagating at the GardenFarm™. It helps me win the race between rooting and rotting.
There are also some natural, organic materials – like seaweed – which don’t stimulate the rooting hormone in a plant, but they can make conditions more conducive to root development.
Sometimes, a leaf-bud cutting – rather than an entire stem section – is the best option to reproduce a plant. A stem is cut just beneath a leaf-bud and cut again just above the bud. The smaller, remaining leaf-bud section will then reproduce a plant from rooting at the leaf node.
Remarkable Reproduction From Leaves
Not all plants require stem tissue for propagation. Instead, the base of a mature leaf – the point at which it attaches to the main stem – can be triggered to generate roots by placing the base in water or moist soil, like a cutting. For some plant species, the leaf will only produce roots from its petiole rather than from the leaf base.
It all comes down to the genetics of the species you’re trying to propagate.
Did you know the leaves of some plants are able to produce roots from their veins? When a small slice is made along the leaf vein, the cells along the cut are triggered to produce roots and foliage shoots – generating a new plant. This is known as the split-vein method and works for species like begonia and African violet.
And then there’s the sansevieria plant (also known as Mother-in-Law’s Tongue or Snake Plant). This iconic houseplant variety is revered for being just about bullet-proof, but it’s also one of the easiest plants to propagate. The long leaves can be chopped into pieces, and the cells along the wounds of each piece will be triggered to produce roots and foliage shoots. Pretty amazing stuff.
How do you know which propagation method will bring you most (or any) success? Do a little research for the specific plant you wish to reproduce. As with any online research, stick with trusted experts in the field or educational (.edu) websites for the most reliable information. Leslie’s book offers a great chart for many common indoor and outdoor plants as well.
When Working with Seeds
Even if you have in your possession a true seed, you may need to provide a little help for germination. Sure, seeds are naturally predisposed to sprout, but consider, for a moment the native functions of different seeds.
The seed of many varieties of spruce tree, for example, has evolved in often frigid winter temperatures of its native habitat. In order to survive, it must be armed for hibernation and, only after spending time in the cold, be signaled to sprout in the friendlier spring warmth.
The seeds of some plants have a tough outer coating as protection from being digested in the belly of birds or other animals. The coating is weakened by the digestive juices, so once expelled from the forager, the plant sprout is able to emerge from the weakened shell.
When a seed is genetically designed to pause until certain conditions are met before germination, we can mimic the required conditions through scarification or stratification.
Stratification mimics the cold hibernation period some seeds require. There are two types of stratification – wet and dry. Mix seeds with slightly-dampened sand in a plastic bag. Seal the bag tightly, and place it in your refrigerator for two or three months. When you remove the seeds, the increase in temperature mimics spring, and germination can begin. This is known as wet stratification.
As an alternative, place the seed and sand mixture into the freezer. Moist seeds will actually freeze and lose their viability, so it’s important that the sand in this method is dry – hence the term dry stratification.
In either case, you are mimicking winter dormancy to trigger the seed to germinate once it’s removed from the cold. Some seeds even require a double stratification period to re-create their natural double-dormancy.
Scarification is for those seeds with hard outer shells. Using sandpaper or a small file, you scratch (or scar) – and weaken – the seed surface. It’s not necessary, or even a good idea, to remove the entire seed coat. Your goal is to create a small weakened area which will allow air and water to infiltrate the outer shell and stimulate germination.
Scarification can be time-consuming when working with a large quantity of seeds, but boiling water can be a big time-saver. Briefly submerging seeds in a pot of boiling water can create the same weakening effect.
If you purchase seeds, the packaging should indicate whether scarification or stratification is recommended, but if you aren’t sure, a little research will provide guidance for the species you’re working with.
Tools of the Trade
When it comes to propagation, there are some products and tools which can give you a leg up on success.
When seeds are so small that they can be difficult to handle, Leslie recommends seeders – which she describes as small puffers with a tiny hole to expel the seeds. These little devices can help you disburse even the smallest seeds evenly into containers. No squinting required.
Whether you’re growing seeds or cuttings, the soil you use will make a big difference. Soilless mix is a good option for seed starting or rooting, because it has been sterilized which decreases your risk of fungal disease. Since it’s lightweight, it also reduces the risk of rotting.
For seed-starting beginners, Leslie recommends the small peat or coir pellets which are widely available at garden centers and big box stores. You just insert the seed and add water – no container necessary. It doesn’t get much easier than that.
Leslie and I both prefer seed-starting mixes which include a little organic matter. They provide small amounts of organic nutrients to get cuttings off to a good start, but these mixes will require more diligence in proper moisture and air flow.
Seeds have all the nutrients they need to sprout, but the small dose of organic nutrients can give seedlings a boost once they’ve set their first leaves.
You may already be familiar with using heat mats when starting seeds indoors. Well, they can also help with rooting cuttings too.
Most plant species require warm soil (picture a sun-warmed garden bed) in order to sprout. Leslie propagates many plants in her unheated garage, so she uses hat mats under the containers to warm the soil to levels conducive to seed germination and root growth. I use heat mats for all my indoor seed starting as well.
The heat can be removed or turned off once the seedling or rooted cutting is established. A good indicator for seedlings is the first true set of leaves. The first set is known as the cotyledon leaves. Those will drop off early on in the life of the seedling. It’s the second set, which are actually considered the first set of true leaves, so be sure to note that important difference when starting plants from seed.
If you’re familiar with hydroponics and aeroponics, there’s a fascinating “aeroponic propagator” that might interest you. It’s essentially a sealed chamber into which you insert plant cuttings. A fine mist of water is continually sprayed on the stems within the chamber, creating ideal rooting conditions.
Leslie recommends these if you are working with plant species which are difficult to propagate – or during times when life just gets too busy to allow you to monitor the cuttings and maintain proper moisture the old-fashioned way.
To really kick things into high gear, you can even add rooting hormone to the misting chamber of an aeroponics propagation. You can bet I’ll be adding a few of these handy items to my arsenal. I’ll just need to decide which size to buy – or maybe, I’ll decide I need one of every model. Stay tuned.
Leslie’s book introduced me to another remarkable tool for plant reproduction. It’s called an “air layering pod,” and it actually attaches right to the plant you want to propagate.
For some of the most challenging plants, the best (or only) way to generate roots is through air layering. The air layering pod makes this technique super easy. Immediately after creating a wound on a mature plant, the air layering pod (filled with coir or sphagnum moss) is positioned around the wound. The pod kit snaps right onto the stem of the mature plant.
The pod and contents keep the area moist. Meanwhile, the tissue surrounding the wound continues to be fed through the mature plant’s nutrient system. The roots sprout from the wound within the pod and continue to grow inside that encapsulated area until they are mature enough to sustain all of the plant growth above the rooted area.
At that point, the pod can be removed, and the stem of the mature plant can be cut off just beneath the new root system and planted into a new container.
Exploring these propagation techniques and tools can open up an entirely new world of gardening and plant keeping. Which have you tried, and what did you reproduce? Share your experience in the Comments section below.
If you haven’t already listened to my conversation with Leslie, you can scroll to the top of the page and click the Play icon beneath the page title. Lots of great information in our conversation – and in Leslie’s book. So, I encourage you to check that out.
Links & Resources
joegardener Online Academy: Master Pests, Diseases and Weeds – my newest online course! Just $47 for lifetime access.
Plant Parenting: Easy Ways to Make More Houseplants, Vegetables, and Flowers, by Leslie Halleck