Pollinating cacti flowers: A How to guide.

Astrophytum mysriostigma flower macro.

Introduction

Pollinating cacti is a pretty straight forward task. All it involves is taking the pollen from one cactus and rubbing it on the female reproductive organs of another. Why do this? Not all cacti are self-fertile, meaning able to reproduce be themselves. In fact, most are not (but some are). Some cacti can do the job all on their own, some are so efficient at self-fertilization they may not even open their flowers! Frailea sp. is a great example of this. Usually thought, when cross pollinated with another plant, the resulting seeds are not only more varied and "strong", you often get MORE per fruit!

There are also many wild animals that will do this for you. Bees, ants, moths, butterflies, flies are just a few of our pollinating friends. When trying to breed specific plants, they can prove to be a pain because you are not sure who was the father. Here we will discuss a technique of hand pollination that ensures you get the cross you wanted, without any messing around or second guessing.

Basic Flower Anatomy

Cacti flowers are distinguished by having an inferior ovary and also developing true leaves below the flower! The ovary is located below the other flower parts. Some cacti have such large true leaves, that they may completely envelope the flower and fruit. In the case of the Dragon fruit (Hylocereus undatus), this is very noticeable.

Anther: An Anther is where the pollen is carried and released from. They are on top of the filament. Filament: Filaments are what hold the Anther. Ovary: The ovary holds the ovules. Once fertilized, the ovary becomes the fruit. Ovule: These are what the pollen fertilizes to become seeds. Perianth: Petals and Sepals. Pericarp: This becomes the fruits skin/peel and inner flesh. This part is made up of 3 parts: Exocarp (outer layer; peel/skin), Mesocarp (fleshy layer, often what we would call "fruit") and Endocarp (layer that directly surrounds the seeds) Petals: The colourful outer arrangement that attracts pollinators. Pistil: Ovary, Stigma and Style. Sepal: These often protect the fruits. Stamen: Anther and Filament. Stigma: The stigma is at the top/end of the Pistil. It is often sticky and this is what catches and holds the pollen. Style: The style is what holds the stigma. Below the style is the Ovary, where the ovules are.

Hylocereus undatus flower cross section. Notice the very style and filaments.

Astrophytum asterias flower.

Hylocereus undatus flower.

Flower Fertilization

In order for the flower to be fertilized, they must have pollen land on the stigma. This can happen in any number of ways, often insects brushing against the stigma with pollen on them.

When the pollen lands on the stigma, it will quickly begin to germinate. After it germinates, it will send a pollen tube down the style to the ovules. This often takes an hour or less in many plants (general). These pollen tubes are the way the sperm is going to reach the egg. Once this happens, fertilization is complete and the seeds begin to develop.

Hand Pollinating Cacti.

Objective

The reason you want to pollinate by hand may vary but it is usually because you want to cross specific plants. Whether it is to gain nicer looking offspring, or to make hybrids or just to practice, the procedure is all the same.

With self-sterile plants, the art of crossing is a very easy one. You simply take pollen from one plant and apply it to the stigma of the next. Self-fertile plants are a little more tricky. Self-fertile means the plant can fertilize itself, and it is often very difficult to be sure the resulting babies were of your own cross or it self pollinated itself. To find out, one usually needs to grow out the plants and compare them to the parents, even then there is doubt.

Hand Pollination

This is actually quite easily done with most cacti species. Some things to consider though is that some species, or cultivars, are more difficult to pollinate than others. Even some individual cacti are more reluctant to put out seeds than others, despite flowering. So if you don��t get seeds right away, don't toss out the idea. *Not every flower provides fruit*.

The idea is to get the pollen and place it on the stigma. Many people use things like Q-tips. These are a bad idea in my opinion. Flowers are a delicate thing, and many cacti have small flowers. For larger species like Trichocereus and Hylocereus, a q-tip may work perfectly because the stigma may be 2+ cm wide! But for small species like Lophophora, Ariocarpus, Astrophytum etc, Q-tips are like using a sledge hammer to put up a picture.

Hand Pollination by Brush

I am a huge fan of paint brushes. It was so nice to finally find a good reason to go cosmetic shopping with my wife. In women oriented stores/departments, there are often little eye brushes for putting on some kind of something to a persons eye. I am not sure what exactly they are for, but they work great for breeding plants! What you want are many fine bristles that come to a nice fine point. More bristles = more surface area for more pollen. The fine point will help you get it into the stigma, as sometimes they appear "closed".

Before and after pollinating flowers, I always dip my brushes in rubbing alcohol. This helps kill any unwanted pollen that may be in the brush from previous pollinations...or from the many pollen grains naturally in the air! Let the alcohol evaporate completely before rubbing your flower with it!

I start by placing my brush right in the middle of all those anthers. Many cacti have a habit of closing in on the style when touched. Lophophora are a great example. When you touch the filaments or anthers, they close in and cover the stigma (like a venus fly trap closes). Once they close, it is very hard to get pollen from them without breaking everything up. It is especially a pain in the butt with self-fertile species, because now you just fertilized it with itself!

Once your brush is in the middle of all those dusty yellow anthers, lightly twist it. This will cause friction and more pollen will end up on your brush. You want the bristles on your brush to look like they are dusted with a yellow dust; the more the better!

Once your brush is "loaded", you can take it over to the plant you wish to pollinate. Sometimes the stigma is closed up. I very carefully, with a plastic toothpick, try to open it up a bit, just enough to get the brush in there. Sometimes they just need another day and they will open up, other times they don't open without help. Take your loaded brush and lightly "paint" the stigma with it. Try and touch most of the surface. Within minutes the pollen should start to germinate if it is compatible.

If the flower remains open more than one day, you may continue to pollinate it over and over, this will increase the chance of fertilization, but be careful with her, she is fragile!

Contaminating Pollen

If you don��t clean your brush and pollinate from flower to flower, you are going to get mixes. If you don't care, then have at it. If you are wanting to make specific crosses, your best to clean your brush after each use. Some plants are readily hybridized and in the cacti world even different species can fertilize each other (Echinopsis is a prime example!).

Other things can screw up your breeding success as well. Ants are an especially bad, or good, pollinator. They are really interested in fruit, and if your plant is flowering and fruiting, they are in it. These guys can pollinate everything if they touch it, and they are hard to notice. Other pollinators like bees and butterflies will cross your cacti as well, but are far easier to spot and keep out.

If specific crosses are your goal, I suggest keeping the 2, or more, plants separated (quarantine) until they have finished flowering. This will ensure that no outside factors mixed up the pollen.

Hybridizing

Many people like to breed 2 different species together to get a "new specie"; a hybrid. Cacti in general are far more rule breaking than other plant families when it comes to classification rules. Supposedly, species can ONLY breed within their own specie. If they can breed together, they are suppose to be the same specie (ie sub-species can cross breed, while species cannot). But cacti, and other plants, tend to break this rule...a lot!

Some groups hybridize more readily than others. Echinopsis/Trichocereus, Astrophytum and Gymnocalycium are all commonly hybridized Genera.

One should realize, however, that when hybridizing the offspring may come out good or bad. Things like colour and shape variations often occur, but ill effects such as prone to rot, not cold/hot hardy, poor root systems or sterility can also result.