Susan Handjian is a garden educator in the San Francisco Bay Area. She was a contributing editor of Plants and Landscapes for Summer-Dry Climates.
By: Susan Handjian , 12:02 AM GMT on September 26, 2012
Lack of confidence may be the single biggest impediment to becoming a successful gardener. One sure way to boost confidence is to know how to make better decisions about the plant selection and care, and knowing about the many different types of plants is a good way to start.
While the terms may be daunting at first, learning a few facts about plant traits will give you a firm foundation as you think about the kinds of plants you want in your own garden. Exposure, size, bloom period, water needs, maintenance needs, all have to be taken into consideration as you begin to make choices, some with long-term consequences.
A tree is defined as a long-lived plant having a permanently woody main stem or trunk (although some species are multi-trunked), ordinarily growing to a considerable height, and usually developing branches at some distance from the ground. However we may define a tree, selecting one is the most important decision a gardener can make.
Trees can be deciduous or evergreen. A deciduous tree loses its leaves at the end of the growing season, while an evergreen retains most of its leaves but shed older leaves throughout the year. If a tree loses many but not all of their leaves at the end of the growing season are described as semi-evergreen or semi-deciduous.
There are two types of evergreen trees, coniferous and broad-leaved. Coniferous trees are the very familiar Pinus (pine), cedar (Cedrus), and spruce (Picea), while the broad-leaved species include Quercus (oak), Ilex (hollies), and Magnolia (magnolias). These terms also apply to a number of shrubs and to a few perennials.
Broad-leafed evergreen Magnolia
Conifer - Picea Picea pungens Blue Spruce
Understanding tree size is crucial. As much as you may love a particular species, unless you have several acres, a tree that can grow to 80 feet in height with a 40 foot spread will be more at home in a park than in a home landscape. Urban gardeners have a large choice of smaller trees, like Cornus (dogwood), many Acer (maples), (Malus) crabapple, and Crataegus (hawthorn).
Trees come in a myriad of shapes: conical, pyramidal, spreading, round, columnar, weeping – the list is very long. Having a clear idea of what these shapes mean in your own space can save you from heartache and frustration down the road. Next to size, the shape of a tree has the potential to bring joy or despair. Below is a chart with some examples of tree forms.
There are genera that include both trees and shrubs. Some growers train large shrubs into trees, but be aware that there are maintenance issues associated with this practice. The shrub will always try to revert to its normal, bushy form by putting out growth from its base. Those errant branches will have to be pruned regularly.
Strictly speaking, a shrub is a woody plant smaller than a tree, with several main stems arising at or near the ground. A shrub does not have a main trunk. They are often categorized by height into tall, medium and small shrubs, a very helpful distinction. They can be deciduous or coniferous or broadleaf evergreen, blooming or non-blooming. As you can imagine, the variety of shrubs is almost endless.
While not always the flashiest of plants, shrubs, along with trees, are often referred to as the bones of a garden, and for very good reason. They are long-lived workhorses that give a shape and feel to a space and can be the centerpieces around which you place shorter-lived perennials, biennials and annuals.
Many shrubs have low to very low maintenance requirements. When clients ask me about a low maintenance garden, I invariably suggest an array of shrubs of different shapes and sizes that depend more on foliage color and shape than on flowers for an eye-catching look.
Remember that within almost all species of plants there are different varieties, which means you have many sizes and shapes to choose from. This is especially important for those of you who have small gardens. You can use a large shrub as a tree. A good example of this is Pittosporum (no common name), a very large genus of trees and shrubs that has many different species. These range in size and shape from Pittosporum undulatum, a 15-20’ X 15-20’ tree to Pittosporum tobira ‘Wheeler’s Dwarf’, a demure ground cover that measures in at 2-3’ X 4-5’.
Pittosporum undulatum - Victorian Box
Pittosporum 'Wheeler's Dwarf'
I don’t want to complicate matters, but must now tell you that there is a category of shrub known as the subshrub. These are dwarfed or short woody plants that have herbaceous tops; in other words, they have the characteristics of both a shrub and a perennial. Two examples are Lavandula (lavender) and Thymus (thyme). Many herbs are subshrubs.You can see the woody base of the thyme plant pictured below.
Subshrub Lavandula - Lavender
Subshrub Thymus - Thyme
Perennials are the showboats of the garden. They just can’t help it – whether demure or flashy, their blooms are what catch and often enchant the eye. It’s often the first choice of novice gardeners, but be forewarned – perennials carry the largest maintenance requirement of all plant types. Facing a garden full of spent blossoms may not be your idea of an afternoon pleasantly spent.
They can be partially woody or herbaceous (mostly green), and many have flowers arising from a basal clump or rosette. Others send up their new stems and leaves from an underground crown.
While they are defined as plants that generally live more than two years, there are short- and long-lived perennials. Examples of short-lived perennials are Delphinium (delphinium) and Leucanthemum ( Shasta daisy). On the other end of the spectrum are Hemerocallis (daylilies) and Rudbeckia (black-eyed Susan). (Paeonia ) peonies are remarkably long-lived, well beyond 50 years.
Leucanthemum - Shasta Daisy - short-lived perennial
Hemerocallis - Daylily - long-lived perennial
One of the most attractive qualities of a perennial plant is that as it ages and matures it can (and must, to ensure continuing bloom) be divided at the end of the bloom season to create many new plants. Some other species also spread their seeds to create new plants the following spring. This means more plants for you and yours – compliments of the mother plant. When you have plants to share with friends and neighbors, personal popularity is nearly guaranteed!
A biennial is a flowering plant that takes two years to complete its biological cycle. When grown from seed, during the first year it forms its roots, stems and leaves. In the second year it blooms, forms flower, fruit or seeds, and then dies. When you buy a biennial plant in a nursery, you are purchasing it in its second year of life. Perhaps the most familiar biennial is Alcea (hollyhock), a garden staple. Less well known is the fact that many vegetables are biennials, such as Petroselinum (parsley), Beta (beets), and (Allium) onions.
Biennial Petroselinum - Parsley
Biennial Alcea - Hollyhock
One of the great values of biennials is that the production of seed means you can save the seeds from the previous crop to plant for next year.
An annual is a flowering plant that completes its life cycle in one year. Think beyond the standard marigold and petunia for a moment. While lovely, bright and floriferous, these popular plants are only a part of the vast array of annual plants.
Did you know that many wildflowers are annuals? Depending on where you live, you can have a breathtaking spring and summer display of flash and color simply by tossing some seeds on the soil surface the previous fall. There is a period when the flowers fade and the plants supporting them dry up and collapse, but each of those plants contains the seed meant to perpetuate the species.
For me, the most exciting part of gardening with both cultivated annuals and wildflowers is the element of surprise for the next growing season. I just can’t imagine my garden without Helianthus (sunflower) and Cosmos (cosmos) and always wonder in what part of the garden all those seeds not eaten by the birds or squirrels will germinate next year. If the seedlings are in the way, move them or simply pull them up. If you worry about increased maintenance, it’s best to stick with plants that don’t have an abundance of bloom or simply remove the spent plants before they go to seed.
Cosmos bipinnatus - Cosmos - annual
Helianthus - Sunflower - annual
A grass is a perennial or annual tufted herbaceous plant, usually growing from rhizomes or stolons, with linear leaves and often showy plumes of small, inconspicuous flowers. Grasses are among the most ancient of plants, dependent on the wind for pollination.
There are many varieties of perennial grasses that make outstanding additions to the garden. If maintenance is an issue for you, check to make sure the species you select does not reseed. While reseeding is desirable in many cases, some grasses have the potential to be garden thugs and even invasive.
For the gardener, it’s the plumes that make all the difference. Some are tall and showy, like Calamagrostis ‘Karl Foerster’ (leafy reed grass), some small and quiet, like the Melica (melic ) . Tucked in among the other types of plants, they create a refreshing change of texture.
Calamagrostis 'Karl Foerster' - leafy reed grass
Melica californica - melic
Ferns are ancient plants, flowerless and seedless with leaf-like fronds and reproducing by spores.
Because they don’t flower, they are usually reserved for quieter places in the garden. Often preferring, even requiring shade, they are great counterpoints to flowering plants.
Most ferns are evergreen, but the cold-hardy ferns are deciduous. Their fronds disappear during the chill of winter and will poke back up through the soil in spring.
They come in a fantastic variety of shapes and sizes, even shades of green. Cyathea cooperi (Australian tree ferns ) can reach a height of 15-30 feet, while at the other end of the spectrum there are a number of ferns that reach a mature size of only a foot or two, like Polystichum setiferum, Alaskan fern.
Cyathea cooperi - Australian Tree Fern
Polystichum setiferum - Alaskan Fern
I hope this discussion deepens your knowledge and understanding of plant types and forms. We'll delve into the nature and value of different plant types in future posts.
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