The Horticultural Trilogy: Light, Soil and Water.

For plants to thrive I look to the horticultural trilogy: Light, Soil and Water. I have found over the years that if you can take care of these three issues in an appropriate way for your plants, they will thrive. Now, they can do pretty well if two are right, but for a plant to be truly happy, and reward you with flowers and to be a healthy, these three needs must be met.

Easy, right!?

It is such an important concept that I will break it down into three parts and focus on water today, with light and soil in subsequent newsletters. It is easy nowadays to look up plants and understand their needs, and this makes it much simpler to group plants with similar needs together or set up your watering to address different plant needs.

If you have a nice sunny bed (6+ hours of sun) filled with Sedum, Salvia, Lavender, Echinacea and Bee Balm, you will find that the Bee Balm needs much more water than the others, so you must supplement the Bee Balm with water. Conversely, if you use too much water to cover the Bee Balm, then the Salvia, Sedum and Echinacea may get leggy and weak while the Lavender may develop a fungus. This is why it is so important to group plants with similar water needs together, as well as soil and light. While we often choose plant combinations for color, we must also consider the cultural requirements.

While many Rhododendrons will do well in a lot of sun, it is important to remember the they will need significantly more water in the sun to keep from burning. There are a lot of plants that we think of as part shade plants that can tolerate more sun, but they need more water.

Now that we have talked about grouping plants with similar needs together, we need to determine how much water is enough and this is largely driven by the type of plant and the nature and depth of its root system.  Perennials and annuals have roots that rarely go much deeper than a foot or so, which is similar to turf grass. We know that these plants can be easily hand watered or irrigated as water can quickly get deep enough into the soil to saturate the roots, but shrub and tree roots are much deeper and broader in their reach. Often bigger plants require a different irrigation emitter or delivery process to provide much more water.

Until you learn the specific needs of your plants, it can be helpful to have some tools to help.  The best and easiest way to see the effect of your watering is a Soil Sampler. You can push it into the ground and get a soil core to see how deep moisture exists in the soil. If you are checking the soil moisture around some Azaleas, you need to make sure water is getting into the root zone in the drip area up to 1.5-2′ down. By looking at the core pulled up by the tool you can see what moisture exists and how long you need to irrigate to get moisture deep enough into the root zone. A more expensive route is to get a Moisture Meter. This is an expensive one that reaches up to 2′ into the soil, but there are cheaper versions to give you an idea.

Trees are the hardest to judge as the roots can be three and more feet deep and they can spread broadly underneath the canopy of the tree. It can take hours to deliver enough water to an established tree. Fortunately this may only be necessary during drought conditions like last year.  Most years, bigger material doesn’t need any supplemental water. However, new tree plantings are tricky to get enough water deep to the bottom of the root ball.

Another important factor is that the deeper the roots, the more access they will have to water in the soil and require watering less often. Annuals may need to be watered very regularly because their roots may only be 6″ deep and the top of the soil can experience rapid evaporation. Moisture deep in the soil does not evaporate and is available longer for root uptake in larger plants.

I go through all of this because watering is not as simple as putting on an irrigation system every three days and not paying attention. Windy 80º days can cause plants to require twice as much water as an overcast 70º day. One of the reasons I include a weather section in the newsletter is to help you look backwards and forward with regard to rain and temperature. Underwatering is the most common reason that plants die as water never gets deep enough to reach the deepest roots, but also beware of overwatering that can kill just as easily.

Use the tools I mentioned earlier, group plants with similar water needs together and pay attention to the weather. Try not to wait for your plants to wilt or show stress as that will only hurt their development. Watering well is as much science as it is feeling. Once you understand what your plants need it becomes a lot easier, at least until the neighbor puts up a fence or a shade tree grows over your bed.

A great general rule that I always says is to water for longer but less often.  Get water deeper in the soil to encourage roots to grow downwards for moisture.

Next week: Soil.