A regular lawn fertilization schedule is your BEST defense against weeds, fungus, and insect damage! We recommend a lawn fertilization application AT LEAST in spring and fall. However, if your lawn is badly damaged, you may benefit from the additional fertilization recommendations listed between the spring and fall dates. The following dates are guidelines for when to make your lawn fertilization applications. Keep in mind that the weather is really what we need to go by. It can dictate an earlier or later application time.

San Antonio Lawn Fertilization Schedule

  • Mid April – Mid May For Spring Lawn Fertilization: Grass must be actively growing to absorb fertilizer properly. After the second mowing of the season, apply a simple 19-5-9 formula for an early green-up. Rainbow Gardens 19-5-9 premium lawn fertilizer is specially formulated for our region. (4-6 weeks earlier for organic lawn fertilizer (Mid Feb – Mid March)
  • Mid May – Early August For Summer Lawn Fertilization (if needed): Apply slow-release 3-1-2 or 3-0-2 fertilizers or a liquid lawn fertilizer like Medina’s Hasta-Gro lawn food.
  • June-September For a Chelated Iron lawn Fertilization Application (if needed): This is not always necessary, but if turf grass looks yellow (iron chlorosis) and weak you could apply a granular or liquid iron supplement. Every second or third month during the warm season should be enough. Hi-Yield Iron Plus granules and Dr. Iron are two excellent choices. Stay away from Ironite……it doesn’t have much effect in our alkaline (high PH) soils.
  • October-November For Fall Lawn Fertilization:  Apply winterizing formulas for winter hardiness. Ratios vary, but make sure they are “winter” or “fall” formulas designed for southern grasses. Rainbow Garden’s 18-6-12 winterizer formula is a great choice These formulas will make lawns winter-hardy and provide for early spring green up. 4-6 weeks earlier for fall organic lawn fertilizer.

*Try your best when applying fertilizers (synthetic or organic) to keep it on the turf as much as you can. Avoid over-spreading onto sidewalks, driveways and streets, as this leads to run off. Fertilizers with iron can stain concrete. Nitrogen and phosphorous are great for the lawn but not for our water supply.

Recommended lawn fertilization formulas for warm season southern grasses in South Central Texas

  • 19-5-9 + minors ……………..(Rainbow Gardens Premium Lawn/Tree & Shrub Food )
  • 18-0-6 + Trace ……………….(Fertilome Greenmaker)
  • 24-0-10 …………………………(Fertilome + Chelated Iron Premium Lawn Food)
  • 18-6-12 + minors ……………(Rainbow Gardens Premium Fall Winterizer Lawn/Tree & Shrub Food)
  • 6-1-2 …………………………….(Nature’s Creation organic – Manure Free)
  • 6-2-4 …………………………….(Texas Tee organic)
  • 3-2-3 …………………………….(Medina Growin’ Green organic)

FAQ’s about lawn fertilization:

What do the numbers on the fertilizer bag mean?

They are the ratio of nitrogen (N) to phosphorous (P) to potassium (K). Nitrogen is responsible for making turf green, phosphorous (slower-acting) promotes root development, and potassium works to feed turf and keep it strong during drought or other stressful conditions.

What’s the big difference between synthetic and organic fertilizers?

  • Both organic and synthetic fertilizers contain active NPK ingredients. It’s the source from where those ingredients come from that is different.
  • Synthetic fertilizers get their NPK from chemicals. Organic fertilizers get their NPK from naturally derived elements, like manure, biosolids, and the like.
  • It’s important to remember that timing for applying organic fertilizer is earlier than applying synthetic since it takes longer to break down and become available for plant uptake.

Should I choose a synthetic or organic fertilizer?

This is a decision you will ultimately need to make, but here are a few differences.

  • Synthetic fertilizers offer quick turn around and fast green-up as their chemical ingredients are more readily available to be used right away in the fertilization process. Synthetic fertilizers are usually less costly.
  • Organic fertilizers take a little longer to work as their ingredients must be naturally broken down and processed in order to be used. However, most organic fertilizers actually increase the health of your soil by improving its ability to digest and absorb the fertilizer ingredients.

Soil Testing

If you continue to have issues with your lawn, even after sticking to a lawn fertilization schedule, it might be time to have your soil tested. The turf on top can’t do much if the soil below is horrible. Follow the Texas A&M Agrilife Extension advice in this link to properly obtain and send in soil samples.


~The Happy Gardener, Lisa Mulroy