Climate and the connection to gardening in home landscapes

Weather, climate and microclimates

It's important to note the difference between weather and climate as you garden. Weather is a set of atmospheric conditions (rain, hail, wind, sleet, snow, sunshine, etc.) that happen over short time periods. Climate, on the other hand, attempts to describe weather behavior or patterns over long periods of time. Climate is what the groundhog predicts, weather is what he experiences on Groundhog day. When planning a garden, climate trends are easier to plan for than weather conditions. 

Weather in North Central Texas can be extreme in most any season, though flash floods and strong winds typically occur in spring and late fall to early winter. In the heat of summer, drought turns lush spring green into brown. Texas rarely receive reliable rainfall amounts evenly applied across the landscape. Some years may be wetter than other years, but drought is the norm, with local instances of drought being a regular occurrence. Currently, the climate of Texas is trending toward widespread, severe drought combined with more extreme weather events that scientists predict will last for years. The good news of drought is that many, many Texas plants are accustomed to life with little water. 

As you plan to garden, microclimates can extend and improve the local conditions in which your plants will live. Microclimates can be as small as your yard or as large as a region, though in our case, we're talking specifically about your home landscape, even as the size of this may vary greatly. Have you ever observed changes in temperature or water availability across your landscape? This is a microclimate and may have been purposefully or accidentally created by plantings or other natural characteristics of the land. 

Precipitation gradients 

Precipitation fluctuation occurs between seasons with a strong precipitation gradient from the east-to-west where the yearly average precipitation drops one inch every 15 miles across the state. This results in different average annual rainfall across Tarrant County. For example, the Blackland Prairie averages 37.5 inches of rainfall a year, while the Fort Worth Prairie receives 32.5 inches of rainfall a year. Understanding these rainfall differences can be extremely beneficial to your gardening and were incorporated in this tool.

Many gardeners refer to the USDA's Hardiness Zones maps that chart average annual winter temperatures across the US. Originally developed to predict whether (introduced) plants could adapt to an area, Ecoscapes does not incorporate data from these maps. This is because the plants that we recommend have evolved to our conditions, including low water, so winter temperatures are not an issue. As the limiting factor, available water is more important to the success or failure of native plants in Texas landscapes than winter temperatures.

One way to ensure success with gardening is to understand and create local microclimates in your home landscape, and this may have a bigger impact on the health of plants. Differential rainfall, temperature, light, shade, humidity, wind, slope, soil (depth and quality) movement of water across the landscape, position of nearby structures, asphalt and even ground cover can serve to create microclimates that you can take advantage of when planting. Here's how to spot them:

  • Buy several small rain gauges and place them in various spots in your landscape. During rainy seasons, note rainfall amounts with some periodicity. It may be best to write down the data once daily (at the same time) after each rain event. Keeping track of this, even over the short term, will provide you an idea of how much rain is dropping in certain spots.
  • Buy a combined soil moisture and temperature meter. TheseSpotting these minute differences may take some practice or small tools (thermometer, moisture meter, mapping), but will be well worth considering when planning to plant your garden. Even if you are moving into new development, there will be differences in these characters to begin with AND you can plan to create microhabitats. Taking time to observe first and then to note them will pay off well as you plan. We've discussed a few of these characters below.

Light, temperature and soil

Light affects plants by providing the necessary spectrum that enables a plant to convert the energy from sunlight into food for itself (and it so happens, for us). Given the wide open Texas sky, light is seldom a limiting factor in the growth of plants. However, it can be detrimental to the plant by heating up the plant and the soil. Mostly, plants have mechanisms to avoid this, either through different photosynthetic pathways, chemicals that protect membranes of the plants and the ability of the plant to transpire -- acting kind of like its own heat pump. How can you understand the effects of light in your home landscape?

  • Observe whether existing plants are wilting in the summer sun. Though plants transpire to cool off, if water is limiting in the environment, then transpiration may not be able to keep pace with the temperature rise of the plant. Some plants in Texas can easily endure life even as they wilt. Look carefully and you'll see plants begin to droop in the hot summer. The key to survival for these plants may be in knowing the intensity and length of wilting.
  • Pay attention to the size and shape of leaves. It's normal for young developing plants (particularly shrubs and trees) to have larger leaves at this stage than when they reach 'adulthood'. However, larger leaves can also develop in circumstances where a tree is attempting to find more light. In itself this is not a bad trait. It is simply telling you that light is not evenly spread across your landscape and the plants have responded by producing larger leaves. Compare the leaves of a single tree or shrub at different positions on the plant. Are they the same size? Are they facing the same direction? Do you notice movement of the leaves over the course of a day?

Trees and grasses can also serve to increase the effects of microclimatic conditions. Historically, Eastern and Western Cross Timbers have more trees than the neighboring Fort Worth Prairie and Blackland Prairie ecoregions. The shade that these trees provide combined with lowered temperatures keep the soil cooler which it turns prevents the water from evaporating as quickly. The treeless prairies don’t have this protection from the trees, but they have more clay in their soils which tends to hold water better than the sandy soils of the Cross Timbers. Also, healthy prairies covered in dense native prairie grasses have lower temperatures as compared to non native grasses. This is likely because of the healthy duff layer that builds up at the base of the grasses, providing an insulating layer to the soil.

Understanding soils in your garden and shade affects are extremely important in managing the garden’s microclimate in relation to precipitation. Soils can be clay or sand based. Clay soils may hold onto water, but too much clay will cause water to run off as compared to penetrating to deeper layers. However, planting can affect positively or negatively the potential for runoff. Conversely, if the soil has too much sand, the water will quickly drain and not retain any water. Soils with a high clay content will crack and shift when they dry out, potentially affecting the roots of the plant. Knowing the ecoregion, soil type, where the garden is located and using native Texas plant species that grow in the specific region allows for the differences in soils and precipitation regimes.

Besides shade and soil, there are many ways to manage the microclimate of a garden to reduce or increase the effects of precipitation. Planting a garden next to or far away from hard surfaces or by the side of a building is a way to manage the microclimates. When it rains the soil absorbs the water, but hard surfaces such as driveways, sidewalks, and roofs cause runoff. This runoff can cause pooling and even flooding to surrounding areas. This can be problematic in the spring during an already heavy rain, waterlogging the soil and damaging plants. It can also help during the summer when rain is scarce to redirect the already limited water to plants and soil that severely need it.

Slope also heavily influences the impacts of precipitation on the plants and soil. If the garden is on top of a hill, or on higher elevation, the water runs off. This may be helpful during a flood, but during a drought losing the water downhill can hurt the plants. The plants at the bottom of the slope can face the reverse of these problems. Plants at the bottom of a hill or slope will be hit harder during a flood, with the excess water rolling off the top of the slope to the bottom. The water can pool up in the valleys and damage plants that aren’t water resistant. During times of drought however, being at the bottom can help when scarce rainfall does occur. Water will run off the hill towards the bottom, allowing the soil at the bottom to absorb more water and create a small water bank and help the plants survive throughout the summer.

Tarrant County and the four differing ecoregions that make up its natural environment, the Blackland Prairie, the Grand Prairie, and the Eastern and Western Cross Timbers, are all impacted by precipitation and drought differently. The different vegetation and soil types that occur in each region can increase or less the impacts of floods and droughts. A one-size-fits-all approach to gardening in Tarrant County won’t work, especially when considering the incredible variety in precipitation and temperature throughout the year. Precipitation varies throughout North Texas in a strong east-to-west gradient, so the Blackland Prairie gets more annual precipitation than the Western Cross Timbers. By managing the microclimate of the garden, the effects of flooding in the spring and the droughts of the summer can be reduced.

© The Botanical Research Institute of Texas. The BRIT Ecoscapes Project is made possible by a grant from the Ann L & Carol Green Rhodes Charitable Trust.