Garden Calendar for September 2020

September used to mean back to school and back to the garden, but this year is different. Summer 2020 was a scorcher in the Southwest, so this September is going to have less chores than usual.

September is Time to Transition

Yes, September is a transition month. The soils are still warm from the summer heat, but the nights are starting to get a tiny bit cooler. What plants really notice though, are the hours of daylight. As the days get shorter, the plant genes are urging them to do that last bit of growing and doing photosynthesis to make sugars and starches to survive the winter. This means that sufficient water in September will be important.

Clean your irrigation filter of calcium buildup with some white vinegar to insure good flow.

Plan to Plant

Usually September is ideal for planting trees and more, but I am going to advise people in Low and Middle Desert to hold off until the tail end of the month at least. (Phoenix and Yuma are Low Desert; Las Vegas, El Paso, and Tucson are Middle Desert.) Meanwhile you High Desert readers should plant!

I wrote about planning for fruit trees this fall on SW Gardening (here), because ordering trees may take time. Its also time to think about planting spring wildflowers, and ordering your spring bulbs. (Article on bulbs is coming later this month).


Garden Tasks for Anytime in September

Tomatoes, peppers, and pumpkins can be fertilized with a high phosphorous fertilizer for fall fruits.

Herbs and lawns should be fertilized with a high nitrogen fertilizer for good fall leaf growth.

Treat alkaline-induced-iron-chlorosis plants such as roses, bottle brush, and citrus. Their soil needs a regular re-application of acidifying compounds such as compost, peat moss, coffee grounds, or 1 cup white vinegar in 4 gallons of water.   Some of you have heard this before – there is no need to add iron! Our Southwest soils contain enough iron. Certain plants simply can not absorb the iron they need if the soil is alkaline.

Chlorosis is yellowing of older leaves – but they remain green along the veins. This citrus may need several treatments to recover.

Avoid pruning fall-flowering plants, like the Mount Lemmon marigold.

Keep pulling the weeds.

Continue regular irrigation of citrus and pecan trees for best production.

Remove any cracked or split fruits from citrus and pomegranates so plant energy is spent producing good fruits.

After Mid-September

Fertilize citrus and landscape plants with a balanced fertilizer for good fall growth. Exception, do not fertilize palms or trees in the legume or pea family, like mesquite.

Divide and transplant iris.  They bloom better for it. (I used to doubt this, but then I experimented.)


September or early October is the month to sow native wildflower seeds for spring display.

Deadhead summer-tired salvias and autumn sages for a burst of new bloom.

Dethatch your Bermuda lawn for October overseeding with winter rye grass.

Learn More about Southwest Gardening

Sign up for my newsletter and I will send you the latest free PDF guide to some aspect of gardening here in The Land of El Sol. Topic changes several times a year and all subscribers get the latest one!

soule-southwest-vegetablesMore about growing a vegetable garden in the cooler months this book

Southwest Fruit and Vegetable Gardening,written for Arizona, Nevada and New Mexico (Cool Springs Press).  This link is to Amazon and if you buy the book there the Horticulture Therapy non-profit Tierra del Sol Institute will get a few pennies – at no extra cost to you.

© Article copyright Jacqueline A. Soule. All rights reserved. You must ask permission to republish an entire blog post or article. Okay to use a short excerpt but you must give proper credit. You must include a link to the original post on our site. No stealing photos.

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