How to Grow Castor Bean (Ricinus) in the Garden and for Floral Design
Castor Beans are as beautiful as they are deadly
Ricinus communis is a popular plant for British borders and home gardeners over the world. Although four to eight seeds can kill an adult human, there’s a lot to love about this plant.
First and foremost is the fact that they are one of the most coveted and favorite materials for our local florists. Seriously, we sell out of every single stem that we can offer (minus the ones we keep for ourselves of course!) and we can never grow enough.
Secondly, castor beans offer a look and presence in our personal garden that is unrivaled by any other plant. It’s broad leaves offer an exotic and striking look that you can’t really get with most other plants - and the fact that it also has the potential to be so dangerous just adds to its appeal and mystique.
Third, castor beans offer a structure and form that is rarely found in other floral materials, being a non-composite flower (zinnias, dahlias and lisianthus all being composite flowers for example) that is also upright and spiky (gomphocarpus being the only other one that I can think of). It certainly adds a very exotic and unusual elegance to any arrangement it is part of.
MAJOR DISCLAIMER: Castor beans are majorly poisonous, so proceed with caution. Never let small children or pets or anyone who might eat any part of the plant anywhere near it.
Starting Castor Beans from Seed
Unless you happen to live near a fabulous nursery that can grow castor beans for you, you’re going to have to start your own plants since they’re not commonly available.
Luckily for us, castor beans are relatively easy to start. They are very large brown seeds with marbled and swirled patterning and spots - very pretty to be honest, with a lovely glossy texture. You’ll want to start them close to your last frost date so that the temperature has warmed up a bit before
I like to start them by soaking them first in water - this allows the seeds to plump up and swell, which gives them a great jump start on the whole germination process. Once they are soaked, I’ll keep them in a sealed plastic container to allow them to start sprouting.
So long as you have them in a warm environment, castor beans sprout quickly and vigorously - the seedpods practically launching themselves off the emerging plantlet that goes on to unfurl its large glossy leaves. Plant the seeds in a larger pot - at least a 2” pot - so that they have room for their root to extend and develop a very nice root system.
Planting Out Castor Beans
You’ll want to plant out castor beans after your last frost - they are tropical plants that won’t survive any late freezes. They are heavy feeders, so into rich soil amended with compost they go. Give them a good watering in and then you’ll need to wait until the heat of summer kicks in.
Castor beans will get tall and big - basically forming a giant shrub by the end of the summer.
It’s actually impressive how large and huge they get - towering over you and swallowing up other plants in the meantime. They don’t really play nice with other, less vigorous plants, so keep that in mind when picking a place to plant them.
If you’re looking to grow them for production of floral material, plant them in a large row or patch by themselves so that they can grow without outcompeting anything else. You may want to corral them if they get too large and floppy - a few T-posts or silver birch posts with some baling twine always works well to corral large floppy plants.
When growing for seedpod production, it’s important to pinch their growing tip so they become bushy and produce multiple stems. We pinch out the main growing tip when they are around 2’ tall or so, which forces the plant to send out multiple sideshoots that will produce flowers and foliage.
Harvesting Castor Bean Seedpods
Castor beans are ready to harvest from when they start displaying their spiky seedpods. Each plant will put out multiple seedpods over the course of the growing season and all of these should be harvested to encourage production and flowering.
To harvest the seedpods, simple time your harvest for late evening/early morning (before the heat of the day) and cut into a bucket of clean water. No hydration needed - just make sure to get them into water.
When harvested properly, castor beans will last up to a week in the vase. They can also be dried and used in dried floral arrangements and wreaths later on (a great source of income for flower farmers in the off season - you can check out our eBook on growing dried flowers)
We sell ours to florists per stem, and usually sell them in 5-stem bunches - the stems can get very large, so you can’t usually band more than five without squishing the seedpods.
Harvesting Castor Bean Foliage
The large dark-colored palmate leaves of the castor beans are quite the show in the garden, lending a tropical feel to any planting they are a part of.
They’re very similar to a fatsia or aralia leaf, and given the use of the two tropical foliages in ikebana, we thought perhaps they could be used similarly as a floral material.
Guess what? They totally can be!
When harvested in the cool of the day and well hydrated, castor bean foliage works well as a foliage. Although the vase life isn’t terribly long (just a few days) they make quite the show while they last.
You do have to wait until the plant is flowering in order to harvest the leaves, and you need to pick leaves more towards the base of the plant to ensure that they have more cellulose in them (which helps to ensure you don’t get floppy stems)
But wait! Aren’t Castor Beans poisonous?
Yes, yes they are. Very poisonous.
You should not ingest the beans, and you definitely should not allow access to anyone that might do so (small children, pets). Even just a little bit is extremely harmful.
So what do you do if you want to grow castor beans?
You can of course warn your clients - particularly if you’re selling directly to retail customers. It doesn’t have to be necessarily plastered over your arrangement - a simple word of warning about the danger of castor beans along with how to keep your arrangement hydrated and last longer should be sufficient.
There are plenty of other toxic flowers that are sold - monkshood, daffodils, poinsettias, foxgloves and sweet peas, lilies and larkspur to name a few. If there’s any chance that a small child or pet might get in contact with them, keep them away just to be safe.
If you’re growing them out in the field, ensure that you pick all the flower stems to prevent them from going to seed. If you have animals like chickens or ducks that may forage in the field, ensure that you keep them away from the castor bean plants as the leaves contain the poison as well.