Plant Selection Checklist for the Texas High Plains Region

Based on your gardening statement, gardening theory, design and style, there is a method to correctly choosing plants. I’ve developed a checklist to refer to when buying plants based on my own gardening statement (that is, to create a beautiful thriving, low water-use, low maintenance, ecologically friendly garden composed of plants of a long blooming nature and plants of interesting and unusual foliage).

Naturally, some of my criteria is subjective, such as how long blooming and what would be interesting or unusual foliage to me. Just as some of your criteria will be subjective, only you can determine if a particular plant is a good match to its intended location. It's not a bad idea to take the time to write out your own criteria for plant purchases. It'll save your time, maintenance and money in the long run.

Plant Selection Checklist

Appropriate plants for our area must be able to fit into these categories:

• Native or non-native
• USDA Cold Hardiness Zones 6 (-10º to 0º) and/or Zone 7 (0º to 10º)
• AHS Heat Zone 8
• Water requirements: Low, or medium
• Soil requirements: alkaline clay, caliche or sandy soil; saline tolerance
• Planting Location: sun or shade, windy or protected
• Maintenance required
• Will this plant be invasive
• Other factors to consider: Mature height of plant, mature width (spread) of plant, mature shape of plant, foliage or flower plant, color of foliage or flower, bloom season, bloom duration

Plants I choose must pass these hurdles, usually in this order, to be considered right for my garden. The importance you place on any particular category will influence your selection process too.

Cold Hardiness

The USDA Cold Hardiness Zones are based only on the average minimum temperatures reached over a period of years. On January 25, 2012, the USDA, in conjunction with Oregon State University, released the new USDA Plant Hardiness Zone Map, a new interactive map that better reflects the variableness in terrain more than any previous plant hardiness zone map. This is the first official re-mapping of cold hardiness plant zones since 1990, not withstanding the aborted may released in 2003 by the American Horticultural Society. This new map uses data from a 30 year period, from 1976 to 2005, previous maps used a much shorter period. As a result, boundaries have shifted across much of he country reflecting many areas with 5 degrees warmer temperatures.

One of the best new features of this new map is the interactive feature. Click on the Interactive Map tab and type in a zip code or click on a spot on the map. You'll be able to click on specific locations for the zone, the actual average minimum temperature, latitude and longitude.

Our area had been designated Zone 6, and now according to the new edition, we are Zone 7. Weather is cyclical and changes back and forth with time. Over any period of years, our minimum low temperatures will average between ten degrees below to ten degrees above zero, depending on your particular microclimate. Even the microclimate in your landscape can vary up to five degrees near a south facing brick wall or boulder, versus an open northern exposure. City lows may vary by up to five degrees versus open country.

For a long time, cold hardiness was the prime factor considered for a plant’s suitability. The main East Coast growers chiefly determined cold hardiness. There is now a greater, more widespread distribution of southwest type plants than before. The inability to withstand cold temperatures in soggy or moist soils distorts the cold hardiness rating previously given them. Plants that are adaptive to dry, well-drained soils tolerate colder temperatures if the soils are dry and well drained in the winter. Many of the cold hardiness ratings given for drought tolerant plants have not been retested, and re-rated under their optimum soil conditions. This is good news for us. With proper drainage and watering habits, we are able to grow a larger selection of drought tolerant, heat-loving plants than previously thought. It is worth my effort and money to trial heat loving, drought tolerant plants that have been rated Zones 7 and 8 for winter hardiness. They may not survive in compacted clay soil, but if the soil is amended for drainage, they have a much better chance in surviving.

Heat Zones

The American Horticulture Society has introduced the category of heat zones, to help gardeners to determine whether plants can take the heat (or lack of it) in their climate. The AHS Heat Zones are based on the average number of days the temperature exceeds 85º. The Texas High Plains Regions falls into Zone 8, averaging 90 – 120 days temperature exceeds 85º. Heat Zone 8 is a fairly moderate zone with many plants falling within this heat tolerance. Heat zones are another guide to help us determine a plants appropriateness for our climate, just as the cold hardiness help us in this determination. We must remember, however, helpful as these guides are, they only indicate one factor of cold or heat – that is the average minimum or maximum. These climate guides do not, and indeed, could not, take into account humidity, wind speed, solar radiation, time of season, and duration of minimums and maximums and whether they occurred suddenly or gradually. These are climate factors not addressed. Other factors not addressed are soil conditions, dry/wet conditions and general health and well being of the plant, and it’s location.

Water Requirements

I am always searching for plants that fit the low water-use category. This is one of my prime criteria. However, I do buy and use plants of medium and high water-use requirements. I simply hydro-zone them into the appropriate area. Determine the water requirements for a specific plant before purchasing, so you will be able to place it in the correct hydro-zone. If your soil is predominately sandy, your plants will require more frequent irrigation.

Water requirement guidelines given earlier are for average climate conditions. One way to determine when to irrigate was to monitor the area's evapotransporation rates. Prior to 2009, the ET rate information was available to gardeners by accessing the Bushland, TX weather station website. That service has since been eliminated from their budget. Potential evapotranspiration is a measurement of the water needed to grow a plant in a particular location. Potential evapotranspiration (pet) comes from the words evaporation (of water from the soil) and transpiration (of water by plants). The potential ET differs daily according to climate. The climate data used to calculate ETo is temperature, dew point temperature (relative humidity), wind speed and solar radiation. I remain hopeful this service will return.

Each plant has its own ET rate, but few plants have had them calculated, even fewer plants have them measured each day. As a general guide, you can use the corresponding ET rate of Buffalograss for low water-use plants, Bermudagrass for medium water-use plants, and fescue and blue grass turf grasses for high water-use plants. H Bar H Turf Farm has provided some general information about ET rates and grasses.

Soil Requirements

The type of soil in your planting location is of paramount importance. If you’ve read the section about soil and have had your soil tested, you have a pretty good idea what kind of soil you have. Many plants have definite soil requirements, others have a good bit of leeway – they’re versatile. Here are some characteristics to keep in mind:

• Basic composition, clay, caliche or sandy
• Alkalinity
• Salinity
• Texture, drainage ability
• Organic content
• Toxicity (for most people, this probably won’t apply)

Please refer to the section on amending the soil for a more complete explanation. For less maintenance, your first choice would be to select plants that perform well in your soil type. If your soil is of poor quality, such as caliche, or the depth of soil is inadequate, you will need to amend the soil for the plants or build raised beds.

You cannot change your basic soil type, but you can amend it to allow for a wider selection of plants. Likewise, you cannot permanently change your soil pH from alkaline to acid, but you can amend it with organic matter to decrease alkalinity. Organic amendments will increase organic content, improve drainage and texture, buffer toxicity and increase the ability of your soil to hold in water and nutrients. Inorganic amendments improve drainage and texture, and some inorganic amendments will also increase the ability of your soil to hold in water and nutrients.

Planting Location and Space

What comes first, the location or the plant? For best results, you should always have a location in mind first, then find a plant that fits the location. Too many times have I bought a plant, then walked around the yard wondering where to plant it. Rarely does this method aesthetically add to the landscape’s composition and design. Know your location first, and then choose a plant with the characteristics that fit.

Sun or shade, windy or protected are the main characteristics to keep in mind when choosing a plant for the area. Naturally, if the location qualifies as a full sun location, choose a plant the needs full sun. Likewise shady plants for shady locations. Most plant tags will provide this information. However, as mentioned in the paragraph on invasive plants, planting them outside their requirements will harness in their aggressive tendencies and become a useful part of the landscape.

If the location is windy, and a windbreak is not practical, small, more compact plants should be considered; perhaps a rock garden would work. Alpine rock garden type plants are suited to windy conditions with a low stature and hairy leaves. The hair on the leaves helps to disperse the wind and reduce transpiration. Ornamental and bunch grasses and plants with tough wiry stems or branches enhance windy locations by flowing with the wind, creating a pleasant sense of motion.

Avoid choosing plants that need staking such as delphiniums and gladiolas if you’d like lower maintenance and a better looking flower bed. Also avoid plants with delicate leaves and flowers that not only will become wind-whipped, but easily desiccated by the wind.

I know it is hard to imagine their mature size when purchasing specimens in small containers. Plants tags generally correctly provide this necessary information. Resist the temptation to carve our narrow beds. Make them wider – the shrubs, trees and herbaceous perennials will fill within 2-5 years. Less turf, more shrubs and perennials translate into lower maintenance; unless you are forced to be constantly trimming and pruning back their natural growth to an arbitrarily unnatural size to fit a small space.

I’m space-challenged, and I admit it. I locate plants too close together, and too close to buildings and structures. Let the plant be whole, not half, and enjoy the fullness of its being, I constantly remind myself. Allow space in between the plants at mature growth as well. In garden design, we creatively shape specific spaces for specific reasons. Use space as a design feature. Our home lots are shrinking. We must keep this in mind in designing our landscape and choosing plants. Perhaps a dwarf or diminutive selection is better. Plant selection for smaller gardens is crucial. Each plant selection should be made with care. In plant selection, I know I have a real, definite space budget that I cannot exceed without removing something already in place, be it a plant, turf grass, concrete, asphalt or buildings.

There are ways to get around the space budget! Dot your patios, walls and fences with containers, even hanging containers on the walls and fences. Containers do elevate your maintenance to a higher, more frequent level – there are many tradeoffs. If wall and fence containers represent too high a maintenance for your time budget, select vines and climbers, either annuals or perennials that generally are very low maintenance (many can be aggressive, however).

Proper spacing between plants allows for lower use of water. For areas with no handy supplemental irrigation, plant fewer plants and space them wider apart. Mulch in-between. Each plant has definite water needs that must be met for the plant to survive and thrive: fewer plants for the available space/water area translates into less watering maintenance.

Maintenance Required, or Just Grow Baby, Grow

Every time I write out this checklist, the amount of maintenance required moves up a notch on the list. The amount of maintenance I want to give a plant is becoming more and more important to me. After I prepare the soil for a bed, I just want the plant to grow, baby, just grow. My list of “plant and walk-away” plants is growing. You must admit this has a certain appeal. I have heard so many gardeners talk about planting a plant, then quickly forgetting to maintain it, or not having the time to maintain it. And then it dies.

There’s nothing wrong with the concept of “plant and walk away’. In fact, many of us have already done this. Have you ever planted a bulb and had it flower 4-6 months later? Of course.

We’d all like to enlarge the list of plants beyond bulbs. All the seven principles come into play to achieve this low maintenance concept. Soil preparation and mulching are keys as are matching the plant to the location. But so is timing. Planting at the opportune time for the plant allows you to walk away quicker. Refer to the right time to plant later in this section. You will certainly not be able to achieve this with even every low maintenance plant, but your follow up during the plant establishment period decreases greatly. Maybe it’s just a quick “look see” to ascertain whether any further care is required, especially beyond supplemental watering.

Invasive?

It makes no sense to create problems for yourself by adding an invasive plant to your landscape. However, sometimes you may choose to plant one, but in the right location where it’s an advantage instead of trouble. Plants can be invasive in one climate, and microclimate, but not in another. Some native plants could be invasive in a garden setting depending on how well you treat it. Invasive plants have honed their survival skills to a higher level. Invasive plants can become bullies in the flower bed – they want to take over the entire location. They are not suitable for a mixed border or cottage garden effect, but could be quite suitable for massing together in the right problem area.

For instance, in a large, dry, sloping area, you need a tough survivor to cover the area with minimal care and soil preparation. Callirhoe involucrata, poppy mallow, or wine cups, is a good native choice. Berlandiera lyrata, chocolate flower, is another. Wine cups spreads nicely so give it plenty of room. Chocolate flower re-seeds prolifically. Native Oenotheras, Hymenoxys, Verbenas, Zinnias and grasses are good to add to the mix. For a large area, a mix of plants is better than a massing of a single plant. Diversity of plant material is better for long-term survival.

For dry shade areas, I use Aegopodium podagraria variegatum, Bishop’s Weed, on the north side of my house. Its leaves tend to brown and crisp in the sun, but in the shade, it maintains it’s pleasant cream and green color. I never water and feed it, but it does benefit from roof runoff. Once a year I need to pull back the roots from encroaching on a row of chrysanthemums. I would never plant Bishop’s weed in sun in a medium or high water-use area. Under these less austere conditions, it not only will flourish, but also rampage. Stachys byzantina, lambs ear, can be invasive too under sunny, moister conditions, so again it is a candidate for dry shade, where it is more respectful of me, the gardener. These are just a few tips; you will encounter other plants previously thought of as criminal, but when held under proper restraint, are civilized.

Vinca major is an old standby, as is English ivy for low water-use shady areas. I have spent hours each year trying to control their spread and have finally taken them out (even more hours spent). They are useful in a larger area isolated from mixed beds and borders.

Plant Aesthetics

Foliage or flower, color of foliage and flower bloom, duration of bloom and bloom season are important criteria. In choosing plants, do not neglect the mature height, width (spread) and shape of the plant. At maturity, will it fit in its allotted space? This is critical to the beauty of your design, the health of your plant, and amount of long-term maintenance. In the past, this category may have been your first consideration in plant selection. I hope it is not anymore. Don’t worry, after vetting a plant for Panhandle appropriateness (USDA Hardiness Zone, AHS Heat Zone, soil, water, location, maintenance characteristics), there is still a large selection to choose from.

Foliage or flower, color of foliage and flower bloom, duration of bloom and season are important criteria. Most of us concentrate on color of flowers. Foliage color offers striking visual interest without the brief or prolonged addition of blooms. Leaves are interesting, as are stems and bark. The flower itself is only one reason to add it to the landscape. Rooms of books have already been written on this matter, so I’ll be brief. I try to remember, after the bloom is off the rose, what is left? Or was that ephemeral beauty enough to sustain interest in the garden to another year? Foliage projects different textures and light patterns just as alluring as temporary color.

If perpetual color were everything, massed bedded borders would hold our attention longer. But it does not. We appreciate the bold stroke of color, but our mind quickly assimilates it and moves on. Intricate combinations of size, shape, texture, color, and time, with the changing nature of the garden through the day and seasons hold our attention. Plants of a long blooming nature and foliage provide the backdrop for solo performances. Designing a great garden is similar to writing a symphony. Each plant has its part to play, at a particular moment or moments, creating harmony, climax, drama and beauty in the landscape. Each bed connecting, flowing one to another, changing and progressing from one garden room to another, a cohesive design, unified by a common theme, ringing throughout the landscape.

Each season brings new delights and surprises. Mature gardeners relish anticipation as much as fruition. If you are musically oriented, each note is a plant to be highlighted or restrained, each grouping a chord, each bed and border a movement in the symphonic melodies your landscape resonates. Notes and chords are repeated for unity and effect. The use of color is the conductor’s baton, striking emphasis here, then there, as the season progresses. Throughout the garden’s symphony, in spring, in summer, in fall, and yes, even in winter, the crescendo of sound emulates in floral display. If we gardeners cannot walk outside our door, even once in each of these seasons, and be “wowed” by our own gardens, our task remains unfinished.

Angie Hanna, January, 2006