Winter Sunlight and Plants

Days are getting shorter. Or, more correctly from the viewpoint of an organism that needs sunlight for photosynthesis, nights are getting longer.  Either way – it’s a tough time of year for many plants, and for people too.

Not Enough Sunlight

Long nights mean there is often not enough hours of sunlight to make enough food to grow. Not just grow but to also do all those complex processes to make the chemicals to protect yourself from being eaten.

In humans we call the response to lack of sunlight “Seasonal Stress Disorder.” It is a normal human response to the problem of less sunlight. I urge you to engage in some horticulture therapy and grow bulbs indoors – like amaryllis.

Horticulture therapy! Plants, and especially flowering bulbs, can cheer up your space.

Members of the Vegetable Kingdom have been dealing with this seasonal stress for eons. Since plants need sunlight to feed themselves, lessening hours of daylight can really have an impact. Even in the sunny Southwest.

As the days shorten, plants respond by slowing down. Many species shut down non-essential systems. Non-essentials include leaves, stems, buds, and almost all growth processes. But in many species, the roots will remain active all winter – which is why we garden writer folks tell you to plant in fall.

Shut Down

This plant “shut down” means that leaves will fall off some trees. In some cases they “change color” first. Technically, the leaf color does not change. Those colors are there all the time. It is just that as some pigment molecules are disassembled for storage, larger, harder to disassemble molecules become visible. The brilliant red colors of autumn maple leaves is actually always there, it is just masked by green chlorophyll pigments.


It Can be Beautiful

Plants shutting down for the winter can be lovely. You don’t have to travel for fall foliage. You can have your own fall foliage display right in your own yard. (See my yard in autumn on my YouTube Channel.)

Growing deciduous trees can make excellent sense in southern Arizona. A deciduous tree can save you a great deal of electricity over the course of a year. First, it shades your home in summer, lowering cooling costs. The leaves drop in autumn, letting the sunlight stream through and heat the walls of your home all winter. Best of all, there are a number of plants that provide fall foliage without excessive water use.

Dill is one of the herbs to grow in the winter in our region.

Save Water

Other season changes experienced by most of your landscape plants include less growth. This means less water. By December first you should switch your irrigation schedule to the winter cycle. Be sure you are not watering your succulents at all right now. This can cause rot problems. However, if you have a winter veggie garden, or winter herbs, or spring wildflowers, or bulbs, now is the time to water them.  More on Growing Bulbs.

Exceptions to the Rule

There are exceptions to every rule, and plants are no different. Some plants start growing in the shorter days of winter. Native plants that grow in winter are the ones with ancestors from northern climates. Surprisingly, this includes the spring flowering brittlebush and the globe mallow.

Non-natives that start growing now include the winter rye lawns that many of my readers plant. Also, all the winter annual flowers we enjoy, like pansy, calendula, violet, snapdragon, Johnny-jump-up, lobelia, alyssum, nigella, lupine, et cetera. (see last weeks article.)

Calendula grows well in the cooler months. It is a pretty flower and the “petals” are considered an herb. I make a soothing lotion using calendula.

Herbs from climates with shorter days also begin to thrive now. Cilantro, parsley, dill, fennel, caraway. Incidentally, all of these are members of the Carrot family. Chives and scallions can be planted now as well, but it is better to wait until after the Winter Solstice to plant the members of the onion family where you use the bulb, like onions, shallots, garlic and elephant garlic. More on Cool Season Herbs.

Indoor Plants

House plants may be stressing due to the reduced light. Most house plants are originally from equatorial rainforests, where the day length never changes. Do reduce watering frequency, and don’t fertilize for a few months.


Lucky for us Southwest dwellers, winter only lasts about four months. By mid-February, many plants will be starting to grow again. The exception? Plants with ancestors from the tropics, like mesquite trees. They will wait until after the local last frost date.

For humans, winter is a great time to get out and enjoy the sunlight we do get. As the holiday season is upon us – I hope you will take some time to de-stress out in your yard or garden.

soule-books-buyNeed some Garden Help?

May I recommend my (out of print) book?  The Month By Month Guide offers tips for your landscape (yes even lawns and roses) in every month of the year.  I have a few copies left and am offering them to you – my loyal readers. Price is what you would pay on Amazon – only when you buy from me you get a signed copy!
From the review:
“A great reference book is key to successful gardening in the region where you live. takes the guesswork out of gardening for anyone residing in the Southwest. With this book, you’ll know what to do each month to enjoy a thriving garden all year, from January to December. Chronologically organized, this guide is full of critical gardening when-to and how-to advice, along with illustrated step-by-step instructions.”

© 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 also include a link to the original post on my site. No stealing photos.

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