What Do You Mean, It’s Not Really a Bulb?

Guest post by Debbie Van Bourgondien “The Bulb Lady”

Sometimes gardeners are accused of speaking a foreign language. More often than not, they are speaking plant Latin when this happens. But often their mysterious language has to do with the root systems of plants.

Most of us are happy to divide the plant world into things that have roots and things that have bulbs. But then you plant one of those bulbs and someone asks if you have a corm or two to spare. Or they call it a tuber, or a rhizome. If you ordered them all from a “bulb” catalog, this can get confusing. “Why didn’t they tell me it wasn’t really a bulb?” you ask?

Well – the horticulture industry also tends to divide the world into things with fibrous roots and things that grow from little packages – bulbs, corms, tubers, and rhizomes. Fibrous rooted plants – those typically sold as perennials – are dirt-dependent and need to be stored in pots. This requires one kind of nursery equipped to do potting, repotting and watering. The rest can often be stored minus dirt when not in active growth – which is an entirely different way of dealing with plants. So you have bulb nurseries, and you have perennial nurseries.

But what do the differences in these terms mean to you, as the gardener?

Well – for one thing, when we take these little packages and go to plant them, it’s nice to know which way is up – and if you know what kind of plant you’re dealing with, you have a better chance of being able to figure that you. Not that it really matters –a plant determined to grow will always find its way to the surface. But let’s make it as easy as possible for them!

For another, all of these little flower packages reproduce in different ways – which means that when we want to increase our supply, or when we want to divide them, it’s good to know what to expect. So that’s what I’m going to explain.

A true bulb is like an onion – it grows in layers and is often covered with the same papery skin that covers the onion. Bulbs that have this skin are usually easy to handle and not easily damaged. Those, like lilies, that lack the papery tunic are much more easily damaged and need to be handled with care.

At the very heart of that bulb is the flower itself – in miniature – but there and just waiting to emerge. It is covered by scales – the layers of an onion in most cases – but in some cases, as with the lily, the scales are loose and swollen, looking more like thin buds of garlic. These scales are held together by a basal plate – a hairy looking plate with the beginnings of roots. Thanks to this plate, not only does the bulb stay together, but we can tell which end of the bulb is up.

A bulb produces offsets – little bulbs attached to the larger bulb – as a way of reproducing itself. Dig them up and it will look like a big bulb-hen mothering baby bulblet-chicks.

Corms, on the other hand, look like bulbs on the outside and often have the same protective sort of covering. They also have a central growing point where the flower will emerge, and a basal plate just like that of the bulb. Crocus, gladiolus, and freesias all grow from corms.

The differences are these: The corm, if you cut it, will not show layers like a true bulb does; it is actually a base for the flower stem packed with nutrients, but quite solid in texture. When the flower starts to grow, the corm shrivels as its nutrients are used up. But at the same time, it creates new corms either on top of or next to the shriveled ones. The original corm dies, but these new corms will usually flower the next season and start the reproductive process all over again. In a few plants, like the gladiolus, the new corms take two to three years to reach blooming size.

A tuber also has a vaguely bulb-like look – although if you squint you’ll realize that it more likely resembles a potato. In fact, a potato IS a tuber – but so are cyclamen, tuberous begonias (surprise!) and anemones, among others.

There is no basal plate on a tuber – in fact it looks quite disorganized about which way it wants to grow. Look at the way eyes sprout all over a potato. All tubers do this – so the best way to plant is wherever you see the most little sprouting tips.

While most tubers just keep increasing in size, a few diminish. However, unlike the bulb and corms, they can be divided simply by cutting them up, making sure that there is at least one sprouting eye per piece.

Some plants are not tubers, but have tuberous roots. This means that, instead of the fine hairs and thin roots we see on perennials, they produce swollen roots that look like tubers. Dahlias and daylilies are like this – if you look at the tuber you will see more than one tuber-like structure of varying sized attached to the plant’s main stems. Where they join together you will see the growing tips of the plant-to-be. You can leave these together to produce one large plant, or you can cut off the individual storage roots making sure to include at least one growing tip (called an “eye”) along with it.

And then, finally, we have the rhizome. Cannas and Calla lilies grow from rhizomes. Like a corm and a tuber, a rhizome is a thickened stem packed with nutrients to nourish the plant that will emerge from it. But unlike the other types, a rhizome creeps along the ground, growing longer and sending up more growing tips as it goes. This makes them very easy to propagate – just cut the rhizome into sections making sure that each section has roots and at least one growing tip or bud.

So you see – the differences aren’t really important if you just want to plant something pretty and relatively – but when you fall in love with a plant’s beauty and want to make more, it really helps to know what you are dealing with. And as spring approaches and the northern gardeners among us start to take their summer bulbs out of winter storage – isn’t it nice to know that you can put more back into the ground than you took from it in autumn?

Debbie Van Bourgondien and “The Bulb Lady” are one and the same. For over 95 years, the Van Bourgondien family has specialized in providing high quality Dutch bulbs and perennials to discerning gardeners. Visit www.dutchbulbs.com to get a FREE subscription to their catalog.


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