The Desert's Extra Season
I talk about two extra seasons here in the desert giving us seven seasons in total!
There is a period between summer and winter and vice versa, where fall and spring come in. I don’t know where I first heard this, but I call these, Shoulder Seasons. They ride on the edges of summer and winter similar to the shoulder on the side of the road.
Sometimes you blink and miss these lovely temperatures, but typically your plants see them as a full season of at least six weeks.
Nighttime temperatures dictate the length of fall and spring’s shoulder seasons.
The Shoulder Season
Our annual and tender perennial flowers both struggle when the temperatures begin to shift. I believe the struggle starts when the nighttime temperatures begin to shift that our seasonal plants begin to stress out.
The Magical Number is 55°F
Think about this –
Desert nighttime temperatures in the summer range from the upper 70’s to 90 depending on your elevation. (Tucson to Palm Springs, Maricopa County, Sierra Vista, Prescott and all communities in between as well as those in Texas, New Mexico and Nevada)
And, in the winter, nighttime temperatures can get into the 20’s but typically in Pima County are 30° to 45°. Of course, lower elevations rarely have a freeze while higher elevations can have freezing temperatures all winter.
Since the changing season of summer to winter is a much more gentle shift, Shoulder Season plantings are easier to plan and IMPORTANT POINT, many plants will continue to thrive through the entire winter, with appropriate care that is. Winter to Summer, aka Spring Shoulder Season, is a little trickier when heat sets in faster than what may be normal and many SS flowers will not continue to thrive as the temperatures climb.
The Desert's 7 Seasons as Defined by Marylee
Summer
The long, hot season that blends or sometimes merges with Monsoon Season. Summer can start as early as late April and go all the way into late September depending on the year.
Monsoon Season
When the majority of our rains hit in the summer. The National Weather Service has defined our monsoon season based on 100 years of history. It officially runs from June 15th to September 15th.
Shoulder Season – Fall
The period between our hot summer and winter. It typically comes from late August and goes until late October. You might be eager to plant winter flowers before the 3rd or 4th week of October but in our desert climate, I strongly urge you to WAIT!
Shoulder Season – Spring
The warming temperatures can stress out some of our winter annuals but the nights are still too cool to plant summer flowers. This is when my recommendations for Shoulder Season plants march in.
Fall – I always joke that if you blink you might miss our Fall season. Many years we finally hit the 90’s and in a week we are headed into 60° days and 40° nights. Now for some northerners, that may be Fall but to me, it’s cold! So Fall can be mid-October through November and it is during this period you can start planting your winter flowers.
Winter
December through early March. We can really plant flowers freely all through the season, keeping in mind to plan to protect tender plants when we have freeze warnings.
Spring
Some years we have a lovely spring. Nights don’t go below 40 and days are sunny and bright with temperatures in the 70’s. Some years we go right from cold to hot. Keep your fingers crossed for a long spring when the heat does not truly it until Memorial day.
The Fall Shoulder Season
We start breathing a sigh of relief when the nights dip into the 60’s. Our summer flowers can appreciate this but much cooler and they start putting on their fall coats, i.e. browning trends of their stems. When we do move consistently in the mid-fifties at night, summer flowers do peter out. They are tired after the hot summer and they are not meant to be cool-season charmers.
We plant summer flowers in our desert pots in late April. You expect these flowers to last until late October, which is six months. Half a year in the desert heat is an unfair request for these plants to thrive and provide you with constant blooms. Their demise will make you crankier in the incessant heat of this hot and dry season.
That is until the monsoons come. And with these unpredictable storms, comes humidity. Now, the northerners would say, “pish tosh, get over yourselves.” But the monsoon and accompanying humidity will jack up the temperatures even more. And when we’re accustomed to humidity levels under 15%, eighty percent of the year, we struggle with the heavy air added to the relentless heat.
If we’re feeling like this, don’t you think your plants have a similar experience?
Don’t wait for October to Act
During monsoon season, some of your plants take off while others are on their last hurrah. The perfect time to trim some things back is during monsoon season. Watch the forecast because pruning is best to do when you see you are going to have cloudy afternoons. If you look at the 10-day outlook and it shows another dry spell, hold off until the dewpoint rises and the clouds start to build again.
If you have some plants that are dead, don’t hesitate to throw them into your compost pile. Unless they look sickly that is, rather than dead. If there is any chance they have a disease, throw them into the garbage.
Hang On Now – this is important
Nighttime temperatures – Summer into Winter
Remember, you want the night temps to get down into the ’50s before you plant winter flowers,
Especially Pansies, Violas, Lobelia, Calendula and Ornamental Kale. And, you want the night temperatures to stay low consistently. I mention these five annual flowers as the worse to plant early because the first three, Pansies, Violas and Lobelia will stretch and get leggy plus when the night temps don’t cool off the way they need, they get weak and spindly. Planting earlier than I recommend is not setting them up to thrive through a long and chilly winter in the desert.
White and Red Ornamental Kale with Rose Pansies
Kale, planted in the heat, will bolt. Bolting means it sends up its flower long before it is time and once it does, you might as well toss it. Remember, plants bloom to create seeds which creates flowers (the bolting ugliness in Kale.) Annuals are ‘done’ after they spread their seeds. They have completed their job. 
Don’t be lulled into thinking that you are out of the (hot) woods when you see a night or two forecasted at 59F. That’s not enough. I can guarantee in the middle desert, that Indian Summer will come with a vengeance and you will be back into the ’90s for 7 to 10 days.
Therefore, I always recommend to homeowners to wait to plant their winter flowers in the last week of October or even in November.
But I Can’t Wait Until October!
I hear you! I often feel the same in August and September. And, when I go to the nursery, I find nothing. Very disappointing. As I list in my book, “Getting Potted in the Desert,” as soon as the growers have them ready, these flowers and more will be delivered to the nurseries. Catch a summary of the plants below!
Keep your potted garden thriving!
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