1. Why Gardeners Call Different Underground Parts "Bulbs"
In gardening, "bulb" is a broad name for underground parts that store food and help some perennial plants survive a hard season, such as a cold winter or a dry summer. An encyclopedia entry (Heibonsha's Sekai Dai-hyakka Jiten) says the shape may be round, lumpy or potato-like, and that these plants are mostly monocots such as those in the lily, amaryllis and iris families [2]. So the group is defined by a job, storing food and resting, not by a shared family tree.
The University of Florida's extension service puts it bluntly: many plants people call bulbs "aren't actually bulbs", because they are corms, rhizomes, tubers or tuberous roots [1]. If they do the same job, what makes them different? It is the part of the plant that swells up.
2. The Five Types: Which Part of the Plant Does the Storing?
Using the University of Florida's definitions [1] together with the Japanese encyclopedia's examples [2], the five types look like this:
- True bulb (leaves). A compressed underground stem surrounded by fleshy, modified leaves called scales. The onion is the classic example. Tulips, daffodils, amaryllis and lilies belong here.
- Corm (stem). An enlarged stem that is itself the food store, with a growing tip on top. Gladiolus and crocus are examples.
- Tuber (stem). Also a stem, but without a basal plate, and with many buds ("eyes") over the surface. Potato is the well-known one. The Japanese encyclopedia lists cyclamen and anemone here, while other sources list different flowers, so lists of tuber flowers vary.
- Rhizome (stem). A stem that grows sideways through the soil. Iris, canna and ginger are examples.
- Tuberous root (root). Fleshy root tissue stores the food. There are no nodes, and buds are found only at the crown, where the root meets the stem. Dahlia, sweet potato and cassava are examples.
Only the first type stores food mainly in leaves. The other four store it in stems or roots. That difference sounds like a small detail, but it changes how each plant grows back.
3. How the Storage Part Decides Where New Shoots Appear
A dahlia's fat, finger-shaped underground pieces are roots, and the University of Florida notes that buds are present only at the crown or stem end of such a root [1]. A practical consequence follows, though the source does not spell it out: a single dahlia root with no piece of crown attached usually will not sprout. In other words, the food is stored in one place and the new shoot starts in another.
An iris is different. Its storage part is a rhizome, a stem that creeps horizontally just below the surface [1]. Because it is a stem, it can carry buds along its length, as stems do. Looking at where a plant keeps its buds is therefore a quick clue to what kind of underground part it has.
4. How a Lily Bulb Differs From an Onion-Style Bulb
Even among true bulbs there are two styles. A tunicate bulb, such as an onion, garlic or daffodil, is wrapped in a papery outer layer called a tunic, which helps stop it drying out. A non-tunicate bulb has no such wrapper. Its outer scales are succulent and separate, and the lily is the common example [1].
A Japanese encyclopedia entry on lilies explains what this means for gardeners: because lily bulbs have no covering skin, they dislike dry places in strong direct sun, so they are planted rather deep and the ground above them is often mulched [4]. The same entry notes that, in East Asia, some lily bulbs without bitterness are eaten. Please do not try eating garden bulbs yourself; many ornamental bulbs are not safe to eat.
5. How Many Saffron Crocus Flowers Does One Gram of Spice Need?
The spice saffron comes from the stigmas (the tips of a flower's female part) of the saffron crocus, which grows from a corm. The University of Vermont's saffron research group reports that one flower yields about 0.006 grams of dry saffron, so about 167 flowers are needed for one gram [3]. Their team found that picking 100 flowers took about 13 minutes on average and separating the stigmas from 100 flowers took about 23 minutes [3]. Adding those figures, and assuming the times scale with the number of flowers (a rough estimate that mixes two measurements), suggests roughly an hour of hand work for each gram.
Why so many? One large corm can produce about 2 to 4 flowers in a good year, and in the first year in Vermont only about half of the corms flower at all [3]. The number of flowers per gram varies with the size of the stigmas, so treat 167 as a typical value rather than a fixed rule.
6. How Japan's Lily Bulbs Ended Up Growing Around the World
Japan has about 15 of the roughly 96 known lily species, and is famous worldwide as a home of lilies [4]. One of them, the trumpet lily (Lilium longiflorum, called teppō-yuri in Japan), grows wild on the Amami and Okinawa islands in the far south of Japan. According to the same encyclopedia, in Europe and North America it replaced the Madonna lily as the Easter flower from the 19th century, which is why it is known as the Easter lily [4].
Kagoshima Prefecture says that on Okinoerabu, an island in its southern waters, trumpet lilies were first grown from wild plants, and that the island exported lily bulbs overseas from the Meiji era (which began in 1868) until about 1985. From about 1980 it also began shipping cut flowers [5]. Total export numbers differ between sources, so this article does not give one. The simple point stands: a bulb stores food that helps a plant grow in the next season, so it can be put in a box, shipped across an ocean and planted there.
7. How to Tell What Kind of Bulb You Are Looking At
Gardeners also sort bulbs by planting season. Spring-planted bulbs, such as dahlia, gladiolus and canna, are tender in the cold. Autumn-planted bulbs, such as tulips and daffodils, are hardy and start growing roots as the soil cools [2]. (This is for the Northern Hemisphere; flip the seasons in the south.) So you have two clues: the planting season, and which part is swollen.
To try this, look at a plant label or photo and guess whether the plant has a bulb, corm, tuber, rhizome or tuberous root. For a true bulb, ask an adult to cut an onion in half from top to bottom and look at the layers. Please let the adult handle the knife. An onion is a useful model because it is the University of Florida's own example of a true bulb [1]. If a plant's food store is a stem or a root instead, the inside will look more solid, like a potato.