Today gardeners and writers of
nursery catalogs use the word bulbs for many
plants that are not, strictly speaking, bulbs. The term has come to include
plants with a distinct underground structure that enables them to be lifted out
of the ground, stored (and even shipped), and then planted again in the ground
to produce foliage and flowers. In most cases lifting takes place during the
resting stage of the plant. (Why such resting stages occur is discussed in some
detail on pages 47—48.) There are always exceptions. Certain plants generally
classed as bulbs are evergreen, and while the greater number of them are plants
that prefer warmer climes, such as Clivia,
Agapanthus
and
certain Hemerocallis, they have the
attributes of being able to be lifted and transported, and have rootstocks or
swollen stems that store food. It is this adaptation, the storing of food in
stems, modified leaves or roots, that more accurately describes the broad
sense of accepted use of the collective noun bulb. Just which forms are taken by various plants, and why, is
worth looking at.
Plants develop rootstocks containing stored food and growth buds for both shoots and flowers, in order for them to survive periods in their native habitats when conditions are not suitable for continued growth. Overcoming that check to their growth caused by cold or drought, lack of moisture or searing heat, requires them to adapt their structure to withstand such adverse conditions, and at the same time, retain the ability to grow again when conditions are favorable. They become dormant during that unsuitable growing time.
Burying themselves deep into the
soil, forming a hard shell to protect the stored food, adapting their leaves,
roots or stems to endure adverse conditions—these are qualities shared by those
plants we group under the word bullb. The
period of time for which bulbs can remain dormant varies. Anemone coronaria, which forms a tuber (but is most commonly called
a corm — it is often
very difficult to distinguish between a corm and a tuber) can easily be stored
for two years or even longer. On the other hand, a Lilium bulb, being composed of fleshy scales that are modified
leaves, will lose turgidity and shrivel unless stored in cool temperatures and
surrounded by material that prevents, to a large degree, the loss of moisture.
Properly stored, it can be kept for 12 months, and no longer. Corms and hard
tubers (a potato is a soft tuber) can be stored for longer periods than a
fleshy bulb (such as an onion) or a rhizome (such as the bearded iris), yet all
of these would be able to withstand adverse dry conditions better than such
fleshy plants as the Clivia.
It is important to understand these
differences, which can be appreciated by just looking at and handling the
various plants. Such knowledge enables gardeners to provide those conditions
best suited for overwintering tender bulbs in colder climates. An Anemone can be kept dry. A lily cannot,
but should be kept moist or prevented from losing moisture. Even as beginners
we can, by observation and the application of common sense, begin to understand
the needs of the plants. They are, in effect, quite logical.
Before considering in greater detail
the differences between the various types of underground storage organs
developed by the various plants in the broad grouping of bulbs, let’s look at
some unusual adaptations of plants.
In certain parts of the world,
particularly in grasslands, there is danger of fire during dry seasons. Fire
sweeping through such areas is a natural event, and can even be welcome. In
fact, certain shrubs need fire before they release seeds, or the seeds need
fire to help break the hard coat that protects the viability of the seed.
In southern Africa there are many
species of Pe/argonium. Among the
popular garden plants we grow in our summer gardens are Martha Washington
geraniums and zonal geraniums, both members of the genus Pelargonium. While they grow in the wild close to the coast where
fire is not common, other species of Pe/argonium
grow in grassland where fires are common. They have developed the ability
to form tubers, sometimes just below, sometimes at or just above the surface
of the ground. Fires sweeping through the area may destroy the shoots, but the
tubers are not damaged. When the fires have passed, new growth emerges.
Other plants
take advantage of fire to survive, and afterward find themselves in an area
freed—for a time—from competitors for available nutrients. If you walk over an
area of the veldt in South Africa that has been scorched by fire, you will be
amazed at how many small bulbous plants seem to pop up and enjoy the recently
cleared areas. Without fire they remain dormant, or produce just a few leaves
in order to maintain themselves, but after the fires have passed, they come into
their rightful glory. They have survived when other competing plants have suffered;
these other plants have to start again from seed, while the bulbous plants,
with established roots and food supplies, can and do take advantage of the
situation to flower and seed. That seed will germinate and small bulbs will be
formed, but they will wait to flower until the competition has again been
reduced to ashes, and the cycle repeats.
But why should such fleshy-stemmed
plants as Clivia and Agapanthus produce their fleshy stems?
One might think they do so to provide a reservoir of moisture to take them
through periods of drought. In fact, Clivia
grow in the shade of trees, not in the open sun. The trees consume moisture
from the soil, and thus when moisture is in short supply, the clivias survive
by using the moisture stored in their fleshy stems.
Agapanthus,
on
the other hand, grow in full sun, and while they don’t compete with other
plants for moisture, they live in areas where the amount of moisture available
in summer is limited. When water is scarce, they can draw on their reserves.
Why does one grow in the shade and the other in sun? I don’t know the answer to
that, but I can tell you that Clivia has
broader leaves by far than Agapanthus, following
the general, and logical, rule that shade-loving plants often have broader and
larger leaves than those of plants growing in full sun. With larger leaves to
catch or absorb as much light as possible, they are adapted to their preferred
locations.
TRUE BULBS
A true bulb consists of leaves
modified for storage and a stem compressed into a flattened plate. The leaves
are attached to the plate. From the plate, roots are produced. Attached to the
plate on the upper side, and surrounded by the modified leaves, is a bud
containing the immature foliage and those cells that will develop into the
flowers. This bud is the entire growth of the coming season, compressed into a
very small area. In some bulbs the embryonic flowers are formed the previous
season, as is the case with hyacinths. In others, the stem arising from this
bud will produce foliage and buds at the apex; true lilies are examples of
this.
Some true bulbs have modified leaves
that are closely wrapped around each other, the outer leaves turning color and protecting
the inner ones. An example of this type of bulb is the onion, with an outer
“skin” (leaves) that becomes dry. Another example is the tulip. (If you cut
through an onion, from side to side, you will easily be able to see the
“rings” which, if peeled off, can be seen to have veins, exactly like those of
leaves. This is not the case with tulips.) Other true bulbs are made up of
fleshy scales, and given good conditions these remain turgid and contribute to
the strength of the bulb. True lilies are good examples of this type of bulb.
How can a gardener profit from such
knowledge? When purchasing tulips, you now know that whether the bulbs do or
don’t have an outer skin isn’t of great importance. (Except that, if tulip
bulbs are offered for sale with the tunics in place, you can be sure that
handling has not been rough, and that unseen bruises are not as likely to be
present. Bruising can cause rotting.) If, on the other hand, you see lilies
with dried outer scales (modified leaves), you know they have not been kept
under optimum conditions and the bulbs have, to a certain degree, suffered. If
many scales are dried, it is not a
good idea to purchase that bulb. If the home gardener is storing tulips, it
isn’t
necessary to keep them moist, but lilies should be prevented from losing
moisture. In our homes we commonly store onions, and no harm comes to them,
even if they are stored for a fairly long period; the “skin” holds moisture in.
Lilium bulbs, not having such a skin,
will lose moisture more readily.
The most
important part of a true bulb is the basal plate. It is from this that the
roots are produced, and the leaves and future flowers and stem also are
attached to it. If the basal plate is
damaged, then obviously the ability of the bulb to perform is impaired. Check
for damage when purchasing bulbs and when you lift and store them. If the plate
is badly damaged, it is best to discard the bulb, as such damage will provide
an entry point for disease. A sound bulb will be plump and firm to the touch with
the basal plate undamaged. True bulbs are generally oval, pear-shaped or
rounded.
CORMS
A corm is a stem that is swollen and
otherwise modified for storage. Generally, the underground portions of the stem
are so modified, and take on a rounded shape, concave on the bottom and
flattened on top. Frequently this storage portion has a brown skin called a
tunic—the basis of the stem leaves. In some cases, notably the crocus, the skin
(tunic) has a meshlike or woven appearance, which can be an aid in the identification
of various species.
Unlike “true bulbs,” corms are
solid. The roots are produced from the bottom, the shoots from the top. The
food for the developing shoots and for the roots is contained in the corm, and
by the end of the growing season the original corm is shriveled, and a new corm
is usually found on top of the old. Clustered around the new corm will be
little cormels, and often, as in the case of Gladiolus, the cormels are very numerous.
When you lift a corm at the end of
the season, remove the old corm and store just the newly formed young corm.
Unless you are going to propagate the cormels and grow them on to flowering
size, discard them. It takes some two to four years to raise cormels to
flowering size. They should be sown in drills, as peas and beans are sown, but
only 1 inch deep. Grow them on for one year, and lift and store over winter.
The following spring, sow them again, a little deeper this time. By the end of
the second season, they should have reached flowering size and can be planted
where you want them to flower. If you live in a warmer climate and leave the
corms of gladiolus, for example, in the ground, you will find the cormels will
send up shoots that look for all the world like grass. If they are not wanted,
just hoe them off.
TUBERS
A tuber is a swollen underground
stem or root, but not the base of the stem, as is a corm. It is usually fleshy,
rounded and covered with scaly leaves often invisible to the naked eye and concentrated
toward the top of the tuber. In the axils (where scales are joined to the
tuber) of these scales, eyes (buds) develop, and it is from
these eyes that the stems and flowers are produced. There are two basic types
of tubers, those formed from the stem, and those formed from roots. The dahlia
has tuberous roots on which there are no eyes; the eyes are found at the base
of the stem. It is essential that dahlia tubers each have a piece of the old
stem with eyes, as the tubers themselves will not produce any new growth,
having no buds.
An example of a root-forming tuber
is the potato, in which the eyes are quite evident. Most people know that if
you leave potatoes in storage for a long time, shoots will emerge from those
eyes. A more attractive tuber is the cyclamen, but there is some confusion, as
many gardeners call the tubers of cyclamen “corms,” however incorrect this may
be. Roots can emerge from almost any part of a tuber, but the majority will be
from the underside, which is generally rounded, while the shoots emerge from
the upper side, which is often concave. In the case of the potato, however,
roots arise from the base of the new stems.
That there
is a difference between top and bottom is a help when planting cyclamen, but
when planting Anemone
coronaria for example, it does not
seem to matter how you plant them —which is
fortunate as it is almost impossible to tell
top from bottom!
RHIZOMES
A rhizome is a swollen underground
stem that has apices (tips) from which shoots emerge. There is generally only
one apex that will produce growth at the time of purchase, but after a season
or two of growth, the parent rhizome will start to produce side shoots at the
end of which shoots will emerge. The roots are produced on the underside of the
rhizome. If you cut into a rhizome you’ll see it is solid,
just like a corm or tuber, but the difference between a rhizome and a corm is
that only the ends of a rhizome produce shoots. In the case of corms and
tubers, growth is from the top. The rhizomes of bearded iris grow with their
tops exposed to the sun. While certain plants have rhizomatous roots and spread
by producing such, these roots are not swollen and do not act as storage units.
Only those roots that are swollen and act as storage units are included in the
broad use of the word bulb.
WHERE DO BULBS COME FROM?
I doubt if there is a country in the
entire world that does not have a bulbous plant growing wild somewhere within
its boundaries. Of the some 250 genera that contain bulbous species, 97 of them
are found in South Africa. Some of them are not well known, such as the genera Depidax, Gethyllis, Hexaglottis and Walleria, but others are well known to
gardeners. Among these are Agapanthus, so
widely grown in the warmer parts of the United States; Amaryllis; Clivia, one of the finest bulbs for winter color in
warmer climes; the glorious Freesia; the
popular florist’s flower, Gloriosa; the
pretty Nerine; the great
container plant Lachenalia; and the
tough Arum lily correctly called Zantedeschia,
now found growing wild in many parts of the world, and indeed often
regarded as a weed in parts of California.
The beauty of many South African
species has yet to be discovered by American gardeners. Some watsonias are
known, but more should be grown, and who knows just what new colors will be
forthcoming when the full range of Gladiolus
that grow wild in Southern Africa are more extensively used in breeding
programs? The angel’s fishing rod, Dierania,
are worthy garden plants, found in a few gardens, but so very worthwhile
they should be grown more extensively. Surely when the unusual colors of such
plants as Ferraria become known,
gardeners will demand they be available commercially. I think it
fair
to say that we have but scratched the surface of the bulbous plants worthy of
commercial introduction. Goodness only knows what marvels of color and form
can be created by devoted hybridizers of such genera.
We often think of plants as coming
from countries with which we associate them strongly, but often those places
are not their true homes. The most popular of bulbs, the tulip, did not
originate in Holland but in Afghanistan, China, Crete, Greece, Iran, Turkestan,
Turkey and other areas around the Mediterranean. Many of our lilies come to us
from China, Japan and Korea, and from species that grow wild in these lands, we
have the forebearers of many of our lovely hybrids. True, there are many lovely
species native to North America, but these are not as popular as the many
hybrids, the progeny of bulbs from other lands.
Some bulbs are found in many
different parts of the northern hemisphere, the iris being a good example.
Irises are not found in the southern hemisphere. However, the family of the
iris is well represented by the genera Dietes
and Moraea, found below but not
above the equator. Snowdrops and snowflakes, Galanthus and Leucojum, are
native to Europe, while North America is home to the splendid Trillium and the Calochortus, commonly known as the Mariposa lily.
With such worldwide distribution it
is
to be expected that there is a bulbous plant for every garden, no matter what
the soil type or the climate. Bulbs are versatile, many having built-in life
cycles that enable them to survive and thrive where other plants can not.
In our gardens today, we could—if we
had the room—grow several hundred different cultivars of tulip. Yet only a
half century ago the exact bloodlines of tulips were unknown. Herein lies a
tale. For many years tulips were appreciated in their native lands. Prior to
the thirteenth century, Omar Khayyam mentioned them in his writing. The first
Mogul ruler of India, Mohammed Barbur, collected them in the early part of the
sixteenth century, and Pierre Belon, a French naturalist traveling at that time
in Turkey, mentions “red lilies,” no doubt a reference to tulips.
In 1529, Suleiman the Magnificent was laying siege to Vienna. The then-Emperor of Austria, Ferdinand I, sent his emissary Augier Ghislain de Busbecq to Constantinople (now Istanbul) to seek peace terms. There the emissary saw fields of flowers, bought some bulbs and shipped them back to Austria, where they came under the care of Carolus Clusius, the court botanist. A little while later, Clusius left Vienna to take an appointment as professor of botany in Leiden, Holland, and he took his bulbs with him. For this reason alone the tulip industry for many years was centered around Leiden.
During the sixteenth century, the growing of rare and unusual plants was much in vogue in Great Britain. The wealthy vied with each other, not only for the largest houses and collections of art, the most lavish stables and other material objects, but also tried to outdo each other with the magnificence of their plant collections. Plants were imported from all over the world, and among them were many bulbous plants.
In his Paradisi in Sole Paradiius Terrestris (1629), John Parkinson
mentions daffodils, fritillarias, saffron flowers, lilies, tulips and many
other bulbs. Such was the interest and demand for new and unusual plants that
seed and bulbs were often transported in diplomatic pouches. Obviously seed was
easy to carry, and bulbs, more easily transported than shrubs or trees, were
also natural choices for such shipments. During the seventeenth century, many
bulbous plants still widely cultivated today were introduced into Great Britain,
among them Agapanthus africanus, from
South Africa, Sprekelia formosissima, from
Mexico, and Hippeastrum reticulatum, from Brazil.
During the
eighteenth century, the number of bulbous plants introduced into Great Britain
was astonishing, and included such well-known plants as Zantedeschia aethiopica, the Arum or calla lily from South Africa; Crinum asiaticum, from tropical Asia; Alstroemeria pelegrina, from Chile; Trillium erectum sessile, from North
America; Tritonia securigera, from South
Africa; Eremurus spectabilis, from
Siberia; and Dahlia variabilis, from Mexico.
Bulbous plants were not only in demand but were introduced into cultivation
from the four corners of the globe. Throughout the nineteenth century, bulbous
plants from the Himalayas, Tibet, Peru, Syria and Uruguay were introduced, and
by the early part of this century, there were few genera of bulbous plants not
in cultivation. It is indeed unusual to find a new genus of plants, but new
species are still being found. (Still, it must be
admitted
that it is rare to discover a “new” species of outstanding beauty.)
Today, we are dependent on the work of hybridizers for new, beautiful
cultivars. But such is the gene bank that has been established over centuries
that, for the foreseeable future, hybridizers have an almost unlimited number
of species with which to formulate lines of breeding.
It is entertaining to read the
accounts of the many plant hunters and explorers who roamed the world on their
quests. When one realizes the rather primitive modes of transportation, the
length of time it took to reach the areas where
many of our bulbous plants are at home, one has to admire the courage of these
people. Their adventures were many, the hardships endured were almost beyond
belief, and yet such was their determination that they willingly went back time
and time again to collect new species. Their rewards were not great (many received
little monetary reward), but their prestige and the admiration of their fellow
plant lovers —who were not as adventuresome —
could
not have been greater.
Yet these men were humble. It was
only after I had known Harold Comber (1897—1969) for a number of years, for
example, that he would recount for me his adventures. He explored vast areas
of Tasmania, traveling on horseback, carrying cumbersome plate cameras with
photographic plates that were heavy and easily broken, nothing so light and
easy to use as rolls of film. He and his exploration party had to shoot their
food if they wanted meat, and spent weeks and often months on their journeys.
As the time for seed gathering is fall, the weather was not always pleasant and
balmy.
Plant hunters must have a tremendous
knowledge of plants. The explorers who have brought us so much knew the
characteristics of the various families, and proper identification of the
various species they came across was essential to their work. How crushing it
would
be to bring back specimens of plants already in cultivation! Because the number
of plants that could be handled physically on an expedition was limited, it
was
critical to spend effort on only new, unknown plants.
Plant hunters had to be
knowledgeable about the needs of the species introduced so they could advise
how best to cultivate them. It was important that precise records be kept of
the latitude and longitude of where each specimen was found—an added chore,
especially as maps of many regions explored did not exist. Many men who were
sent to remote regions of the world as missionaries had an interest in plants.
Two we must thank for many introductions from China —among them the genus Nomocharis —were Pere Jean Marie Delavay (1838—1895) and Armand David
(1826—1900). Many plants have been named in their honor. Their writings
inspired others to hunt for plants in China, a country that rightly deserves
the name “Mother of Gardens,” as many fine plants, shrubs, trees and bulbous
species were found there.
Information on how to grow the
various new plants introduced was often sketchy, to say the least, despite
often copious notes by those who discovered them. The lovely Peruvian lilies, Alstroemeria, were brought back from South America but for some reason
didn’t survive in cultivation. Harold Comber was sent out in 1929 to rediscover
this lovely genus. It is thanks to his efforts that this plant was
reintroduced, and florists the world over owe Harold a deep debt of gratitude,
as do all of us who admire these plants in our gardens or arrangements.
has a brown skin called a tunic—the
basis of the stem leaves. In some cases, notably the crocus, the skin (tunic)
has a meshlike or woven appearance, which can be an aid in the identification
of various species.
Unlike “true
bulbs,” corms are solid. The roots are produced from the bottom, the shoots
from the top. The food for the developing shoots and for the roots is contained
in the corm, and by the end of the growing season the original corm is
shriveled, and a new corm is usually found on top of the old. Clustered around
the new corm will be little cormels, and often, as in the case of Gladiolus, the cormels are very
numerous.
When you
lift a corm at the end of the season, remove the old corm and store just the
newly formed young corm. Unless you are going to propagate the cormels and grow
them on to flowering size, discard them. It takes some two to four years to
raise cormels to flowering size. They should be sown in drills, as peas and
beans are sown, but only 1 inch deep. Grow them on for one year, and lift and
store over winter. The following spring, sow them again, a little deeper this
time. By the end of the second season, they should have reached flowering size
and can be planted where you want them to flower. If you live in a warmer
climate and leave the corms of gladiolus, for example, in the ground, you will
find the cormels will send up shoots that look for all the world like grass. If
they are not wanted, just hoe them off.
TUBERS
A tuber is a swollen underground
stem or root, but not the base of the stem, as is a corm. It is usually fleshy,
rounded and covered with scaly leaves often invisible to the naked eye and concentrated
toward the top of the tuber. In the axils (where scales are joined to the
tuber) of these