Brown lawns seem to be everywhere in South Florida this time of year.

Don’t fret. Your current turfgrass is likely not “bad” and in need of replacement.  It may just need a little more attention to irrigation during specific times of the year.

The info-graphic below found on the Broward County, Florida website helps to give a better idea of what is happening.  The graph plots Typical Rainfall against Plant Needs to determine how much extra water is needed.  We can see that Typical Rainfall comes close to, meets, or exceeds Plant Needs most the year, but has significant deficits in February, March, April and May.  This means that Florida lawns receive sufficient irrigation from rainfall most months of the year with supplemental water (irrigation) required in February, March, April and May. Hence, year after year, Florida lawns turn brown in spring and grow at a breakneck pace in the summer.

GRAPHIC SOURCE: http://www.broward.org/NaturalResources/WaterResources/Pages/Outdoor-Water-Conservation.aspx

 

The graphic provides a very good snapshot of what is going on, but lacks the actual data points. The two variables, Typical Rainfall and Water Needs, vary significantly from region to region.  If we can quantify these numbers, we can get a better idea of the actual amount of ‘extra water (that) may be needed’ at our particular sites and, more importantly, when.

Typical Rainfall, or the historical amount of rain that an area receives each month, can be determined using Average Monthly Rainfall data. Plant Water Needs can be quantified using Evapotranspiration measurements plus a coefficient for individual plant species.

Evapotranspiration (ET) is a term used to describe the water consumed by plants over a period of time. Evapotranspiration is the water loss occurring from the processes of evaporation and transpiration.

Evaporation is the process by which water changes from a liquid to a gas or vapor and is the primary pathway that water moves from the liquid state back into the water cycle (as we spoke about in a previous article A Simple Trick to Help You Become a More Successful Gardener!). Water can be evaporated from surface water (lakes, oceans, ponds, etc.) and the ground.  

Transpiration is essentially water evaporating from plant leaves.  Think of transpiration as what a plant “sweats out” (perspiration) on a hot day.

Factors that affect ET vary greatly from region to region and are influenced by solar radiation (primary), temperature, humidity and wind.  Site specific ET rate coefficients also include soil characteristics, plant types and even stages of plant growth.

For my particular site in Fort Lauderdale, Florida (sub-tropical zone 10B), I used numbers for Typical Rainfall, as determined by Average Monthly Rainfall for Fort Lauderdale, Florida, and Water Needs, as determined by ET Rates in my areaNumbers are shown below.

Water Needs Chart Data

Putting these numbers into a graph helps to see things more clearly.  Again, this is a macro view that only compares Typical Rainfall and ET.  ET calculations do not include a coefficient for plant (turfgrass in this case) or soil types on my particular site.

Water needs Irrigation chart graphic

 

We can see from the graph above that my landscape will likely need supplemental irrigation during the months of Dec, Jan, Mar, April.  My observations of a brown lawn and wilting plants this spring help to validate my numbers.  Unfortunately, I can also see that I am in store for a lot of growth and mowing from June through October, which is great for my tropical fruits but bad for my back!

How do Average Monthly Rainfall and ET Rates correlate at your specific site?  What months, if any, does rainfall meet plant needs? What months will you likely need supplemental irrigation?

To lessen the impact on both our wallets and the environment, it is best to irrigate all plant material on as as-needed basis.  At my site that means some in the fall and winter, more in the spring and virtually none in the summer.  This can vary from plant to plant (think fruiting tomato vs natives).  Additionally, time between rain events should also be considered.  A good Florida summer rain storm can drop a couple inches of rain in a week, but then it may not rain for another 7-10 days. Local water restrictions, such as the year-round water restrictions imposed by the South Florida Water Management District, should be adhered to when setting up automated irrigation schedules.

Further water and cost savings can be identified by taking a hard look at our current landscapes.  “Do I really need to keep that small section of grass in the side yard and continue to pay for its upkeep or can it be replaced with Florida-friendly plantings which do not require additional irrigation and will provide many more benefits (wildlife, passive cooling, stormwater control, etc.)?”

It is also wise to keep the months of higher rainfall in mind when planting new trees.  If rainfall will water-in my new plantings, then I don’t have to do it by hand!

Happy gardening and embrace the rain!

 


 

Article Information Sources:

http://www.broward.org/NaturalResources/WaterResources/Pages/Outdoor-Water-Conservation.aspx

https://water.usgs.gov/edu/watercycleevapotranspiration.html

https://water.usgs.gov/edu/watercycleevaporation.html

http://ccc.atmos.colostate.edu/~coagmet/extended_etr_about.php

Average Rainfall: http://www.intellicast.com/Local/History.aspx?location=USFL0149

ET Rates:

Abtew, Wossenu; Obeysekera, Jayantha; Irizzarry-Ortiz, Michelle; Lyons, Danielle; Reardon, Anna (January 2003). Evapotranspiration Estimation for South Florida (Technical Report EMA #407). Retrieved from http://my.sfwmd.gov/portal/page/portal/pg_grp_tech_pubs/PORTLET_tech_pubs/ema-407.pdf

ET(mm/d) values in Table 2, p. 7 multiplied by number of days in that month and converted to inches

https://www.sfwmd.gov/community-residents/landscape-irrigation