Fertilize now – as the season turns towards Fall.

Fall is for Fertilizer

It is not officially Fall yet (starts September 21), but summer is winding down, and plants know it. For them the nights are getting longer, the suns rays slant in the sky, plus the ground starting to cool off. Plants that go winter dormant are already starting to store in their roots what they need for next year. Yes, even desert plants go dormant, or at least slow down, in winter.

Science Nerd shares – how plants “know.”

No, plants don’t have brains – but they have genes that help them survive the billions of years that they have survived. Basically they do have some very well honed genes that track how active their chlorophyll molecules are each day. Chlorophyll needs daylight and so more darkness means less chlorophyll molecule activity. When the hours of darkness are greater than a certain number (based on species) genes are triggered to do certain plant activities – like change leaf color, drop leaves, send nutrients into the roots for storage, and more.

If you like to see leaves change color in your yard – be sure to read this article – Desert Plants for Fall Color.

Help Your Plants with Fertilizer

Get Ready for Later

To help your plants get ready for fall and winter – and for wonderful flowers and fruits next year – now is a good time fertilize. Yes, now while it is warm. Fact is fertilizer may trigger some new growth. Fertilizer just before fall will ensure that any new growth you encourage with fertilizer will have time to toughen up and withstand winter – especially if we have another icy one like back in 2011.

Recover from Summer

Fall fertilizer can help plants if they got too much water over the summer and are suffering minor nutrient deficiencies.

Read the Fertilizer Label

All fertilizer labels display three numbers in a ratio to one another. (It’s not just a good idea, it’s the law.) The three numbers are always in the order of nitrogen, phosphorous, and potassium.

In chemical symbols, that’s N : P : K.

Nitrogen (N) is used to make chlorophyll and proteins. Nitrogen stimulates vegetative growth. Deficiency symptoms are pale green or yellow-green leaves and dwarf or stunted plants.

Phosphorous (P) is key for flower and fruit formation, and required for healthy stems and leaves. Deficiency symptoms are excessive fruit drop or leaves and stems that are stunted with purple or red discoloration.

Potassium (K) is needed for general growth and development, including the thickness of plant cell walls. This is important to help plants resist the stresses of heat, cold, wind, drought, insects, and disease. Deficiencies are seen with weak stems, and yellowing or browning of leaves at the tips.

Armed with this NPK knowledge, look again at the three numbers on the fertilizer package. High nitrogen fertilizer is best for plants grown for their leaves, like lawns and palms. High phosphorous fertilizer, also called bloom fertilizer, is especially important for flowering and fruiting plants like iris, salvia, and citrus. Potassium is useful for all plants, but especially important for newly planted landscape plants.

Thrice per Year

Fertilize your landscape plants three times per year for good growth and plant health. You can fertilize more often, but not all my readers are avid gardeners. For most homeowners in the desert, you should ideally fertilize in early spring, early summer and fall. Skip fertilizer in mid-summer even if you are used to doing it back East. The Southwest is a different place.

Skip the Legumes

One major exception to needing fertilizer is the legume or pea family. No need to fertilize legumes, they make their own with the help of bacteria in their roots. Indeed, fertilizer can actually stunt their growth. This includes mesquite, palo verde, acacia, Mexican bird of paradise, snail vine, and many more.

Show Your Plants Some Love

Lavish a little fertilizer on your plants this fall, deficient or not. A tad bit of TLC right now and they will reward you in the year to come.  You could think of it as their back-to-school supplies.

Because we live in Litigious times

Always read and follow label directions for any chemical compound, and this includes fertilizers. Too much fertilizer can kill the plant you want to help. When in doubt, err on the side of caution. You could apply half-strength fertilizer two times, waiting two weeks between doses. Caution is also good with slow growing succulent plants, half-strength fertilizer is often enough for their needs.

Fall means Dr. Soule returns to Pima County Libraries with a number of free lectures. After each talk she will sell and sign her local gardening books. More information on the Facebook page, Gardening With Soule, or you can sign up for the newsletter.