Annuals, Perennials and Biennials

I think there are no more misunderstood terms in gardening than annuals and perennials. So often in print and conversation, one would get the impression that cold hardiness and length of bloom are the chief criteria in determining whether a plant is an annual or perennial. Nothing could be further from actual fact.

An annual is a plant that germinates, flowers, sets seed and dies, generally in one growing season. A perennial is a plant that require one or more growing seasons to flower and set seeds and may live for two or many more growing seasons, not indefinitely. Nature being what it is, there are always exceptions, but generally, this is how annuals and perennials are correctly termed.

There are also biennials; short-lived perennials and sometimes that rather gray middle ground area of hybrids bred for continuous bloom without forming viable seed. No matter what category the plant falls into, cold hardiness, and bloom duration are not factors in classifying it as an annual or perennial. A perennial may or may not be cold hardy for our climate, but it is cold hardy somewhere. An annual will die after setting seed here, in the East Coast, West Coast, England or the Equator or anywhere it could grow. The terms annuals, perennials and biennials refer to the plant’s reproduction pattern.

You will also run across the terms herbaceous and woody perennials. An herbaceous perennial is a perennial that has soft green growth and dies back to the ground in winter and comes back again in the spring, as opposed to woody perennials, such as shrubs and trees, with brown woody growth that does not die back. If the herbaceous perennial is not cold hardy, the soft succulent green growth will die back, as will its roots and will not emerge in the spring. Woody perennials can certainly be non-cold hardy, just as any herbaceous perennial may or may not be cold hardy for any particular climate.

Low, Medium and High Water-Use

These terms are relative to a climate, location or biome. For the purposes of this website on gardening in the Texas High Plains region in clay and caliche soil, this is what I mean when I use these terms. Sandy soil will require more frequent irrigation.

A low water-use plant should receive a minimum of one inch of rain or irrigation each month during the growing season to thrive beautifully in soil amended for low-water-use plants during average climate conditions.

A medium water-use plant should receive a minimum of one inch of rain or irrigation every 2 weeks during the growing season to thrive beautifully in soil amended for medium water-use plants during average climate conditions.

A high water-use plant should receive a minimum of one inch of rain or irrigation each week during the growing season to thrive beautifully in soil amended for high water-use plants during average climate conditions.

This is under average climate conditions. If, during the summer months, we run into a stretch of particularly hot and windy weather above our average high temperatures of 90º to 93º, you may need to water more frequently. Use your best judgment. Our goal is to maintain a beautifully thriving garden, but without the excessive use of water. Plants have a wide range of adaptability. Other factors to consider in the timing of supplemental irrigation are our mulch layer, soil organic content and drainage, and amount of afternoon shade. Sandy soil will require more frequent irrigation.


For purposes of this website, when I talk about water use, I refer to water use in clay and caliche soil, primarily. Although most Panhandle soils are low in organic content, most gardeners are faced with either clay or caliche soil; however I know gardeners that also garden in sandy soil. Sandy soil is different, having good to way too much drainage. I garden in clay soil and have amended it for years for both organic content and to increase its drainage ability. Caliche soil is more similar in that respect than sandy soil.

If you have sandy soil, your goal will be to increase the water and nutrient holding capacity. Having never gardened in sandy soil, I don’t feel qualified to offer advice on how often to water plants, or how much soil amending is needed.

Sun and Shade

Full sun is normally considered 8 or more hours of sunlight a day. When reading reference books from the overcast climes of England and the Pacific Northwest regarding plants requiring full sun, we can fudge a bit. Six hours of our intense afternoon sun is adequate. What about morning sun and afternoon shade? Almost any plant put in our Texas Panhandle’s full sun, but receiving a respite in the afternoon with shade, is improved. Locations receiving four hours of afternoon sun should be considered sun locations for those heat-loving plants. These locations may not provide enough sun for robust flowering, but at least your plant will survive.

Part shade/part sun is usually defined as 4 – 6 hours of sunlight. It is probably best to avoid placing plants requiring part shade in locations that receive afternoon sun. All shade with no sunlight, all day dappled shade, or less than four hours of sun is usually classified as shade. Deep shade is little or no sunlight at all.

Natives, Adaptables, Plant Allies and Exotics

You will find the terms natives, adaptables, plant allies and exotics often as you read and learn more about plants.

When is a native plant, native? Is a plant native if it is grown within the North American continent, in the United States, in the state of Texas? Is it native if it is found living unaided in a natural environment within a 200-mile radius, a 100, or 50-mile radius?

The U. S. Dept of Transportation, Federal Highway Administration, after conducting a survey in 1993 of state highway departments, uses the definition "those herbaceous flowering plants that were known to exist in a region or a State at the time of European settlement". Since the survey, the Federal Native Plant Conservation Initiative, an interagency group formed by a Memorandum of Understanding (MOU) in 1994, has defined "native plant species" as "one that occurs naturally in a particular region, state, ecosystem, and habitat without direct or indirect human actions." (www.fhwa.dot.gov/ENVIRONMENT/rdsduse/rdus3_2.htm)

In determining whether a plant is native, we are interested in it’s historical introduction to primarily a habitat or ecosystem. A plant might grow here, but not there, depending on the microclimate. Also, if you live on the plains, and not near a stream or underground water source, a plant in our general ecosystem may be native to a riparian area, but not native to the open, dry, windy, and shade less plains. Being native does not mean it will be drought tolerant.

If we can somehow determine the plant was native to the habitat prior to European settlement, we can generally conclude it is a native plant. Native plants have the added advantage of providing food and shelter for the fauna of the region. They are a vital component of the ecology of the area. Native plants are desirable for their attraction of bees, birds and butterflies and other pollinators.

An adaptable is a plant native to another country or continent of similar climate and conditions that is able to thrive well in our climate and conditions. It is a plant from a similar floristic region. There are many, many adaptables suitable for use in our gardens.

Adaptables may, or may not, provide food and shelter for the fauna of the region.

In horticultural terms, two definitions of plant allies are used. Familial plant allies are plants from the same botanic families or genera (Ann Lovejoy, Ann Lovejoy’s Organic Garden Design School). Knowing about the concept of plant allies is of practical use to gardeners as they begin their plant selection for creating a particular garden style. Let’s say you are planning an English cottage garden for our High Plains Region, using low water-use plants. Many gardeners might be enticed to choose a catmint, Nepeta, (Nepeta sibirica, specifically) for the garden. There are many different species of catmint to choose from, some requiring high and medium water use.

Are there any catmints that only require low water-use you might ask? Yes, a few! Two of them are Nepeta x faassenii ‘Walker’s Low’ and ‘Select Blue’. Not quite as tall as Nepeta sibirica, but not invasive and enticing to felines either. With over 250 species, you may even be able to find one more suited to your garden style. For a slightly moister area, such a medium water-use area, try N. ‘Six Hills Giant’. If nothing interests you in the Nepeta genus, search other genera within the Lamiaceae or mint family, such as the Salvias. An excellent drought tolerant, blue flowering salvia with gray leaves for our alkaline soil that grows to roughly 30” tall is Salvia chamaedroides, or New Mexican Blue Sage. In 90-95% of the time, you will be able to find a low or medium water-use plant to use in substitution for most garden styles.

Another use of the term ‘plant allies’ is in habitat gardening, a type of naturalistic gardening. Plant allies are plants that are usually found growing together or in association with one another in a native plant community. Often these plants are not of the same family or genus.

Exotics could mean a number of things. Chiefly, “exotic plants can be thought of as those plants which did not originally occur in the ecosystem, and have since been introduced to the area." The National Park Service (NPS) defines an exotic species as, "those that occur in a given place as a result of direct or indirect, deliberate, or accidental actions by humans." This somewhat conservative definition of exotic species is necessary to insure that natural resources in national parks are preserved.” (www.npwrc.usgs.gov/resource/plants/explant/intro.htm). Exotics have come to mean non-native plants that become invasive and crowd out native vegetation, thereby changing the native ecosystem. These invasives have no natural enemies to keep their population in check. The introduction of invasives has been going on for centuries and in some areas of the country invasive plants are a major ecological problem. Plant breeders trial new plant introductions to determine whether they will develop a tendency to escape into the wild and colonize. However, given the widespread distribution of plant material, new introductions are not test-grown everywhere and mistakes can still be made.

Another common definition of exotics is simply something quite different from what grows native to an area, such a tropicals and subtropicals, both from arid (cacti and succulents) and from rainy regions (the large foliage plants such as bananas, alocasias, colocasias, gingers, etc). These, of course, would not become invasive, as they require a higher degree of garden maintenance to thrive under our climate and conditions. They add zest, fascination and interest to the garden and often do not winter over, unaided.

Angie Hanna, January, 2006

Other Plants Articles