When to Start Seeds Indoors: A Seed-Starting Guide for Low-Desert Vegetables
In the low desert, I start seeds indoors year-round. Warm-season crops go under my lights in winter. In early summer, I start tomatoes and peppers again for fall planting. Cool-season vegetables get started inside at my kitchen table while it’s still too hot to plant them out. The indoor timing is what makes the outdoor timing work, and the low-desert timing is different from other parts of the country.
This guide covers which crops I start from seed indoors, which ones I sow straight into the garden, and when to start each one. Low desert here means elevations below 3,500 feet in the Southwest, including the Phoenix and Tucson metro areas.
If you are unsure how to start seeds indoors, this article shares how to successfully start seeds indoors.
Key Takeaways for When to Start Seeds Indoors
- In the low desert, I start seeds indoors year-round, using indoor timing to determine outdoor planting.
- Growing from seed offers advantages like cost savings and a wider variety, crucial for timing in the low desert.
- I also use transplants for long-season crops, which need a head start to thrive.
- Some crops, like beans and carrots, do best when direct-sown in the garden rather than started indoors.
- The article includes a chart with specific planting dates and tips on hardening off seedlings for outdoor conditions.
Why I grow from seeds
Growing from seed has real advantages. Seeds cost less than transplants. You get a much wider variety, so you’re not stuck with whatever the nursery happens to have in stock. And the reason that matters most to me: seeds let you plant at the right time for your own garden. In the low desert, getting the timing right decides more than almost anything else.
For the varieties that have grown well for me season after season, see my favorite seeds.
When I reach for transplants
Transplants earn their place too. Long-season crops like tomatoes and peppers need the head start a transplant gives them. Transplants are convenient and more predictable than a tray of seeds. They put a harvest in your hands sooner, and they hold up better against pests than tender young seedlings.
Crops I usually direct-sow
Some crops resent being moved. Their roots do best left undisturbed, so I usually sow them straight into the garden rather than starting them inside.
Best direct sown:
(Click on the crop name for seed sources.)
Garlic and potatoes aren’t grown from seed at all. Garlic goes in as cloves, potatoes as sprouted seed potatoes, and both do best planted right where they’ll grow. If you want the technique for sowing outside, I cover it in “How to Plant Seeds Outside“.
What I start indoors and transplant out
Vegetables with a long growing season do best when started indoors and then moved out as transplants. These are the ones I rely on for my grow shelves.
(Click on the crop name for seed sources.)
Long-season vegetables I grow from transplants:
Some seeds are slow to germinate and do better under steady conditions inside:
Others grow fine either way, from seed or transplant:
- Bok choy
- Broccoli
- Cabbage
- Cauliflower
- Chives
- Collard greens
- Kale
- Kohlrabi
- Leeks
- Lettuce
- Malabar spinach
- Mustard greens
- Okra
- Onions
- Roselle hibiscus
- Spinach
- Swiss chard
Where I start seeds indoors
My process is simple. I fill my seed trays with seed-starting mix outside, water them well, then bring them to the kitchen table to plant the seeds. From there, they go under lights. I keep a grow shelf with lights running in my office year-round, and when that fills up, I bring in a second wire rack.
The garage doesn’t work in summer. It gets too hot to start seeds well, and some crops, like lettuce and onions, want it cooler still, closer to 60 to 70°F, before they’ll sprout. Sometimes in the winter, I need to use heat mats if the indoor air temperature isn’t warm enough. Here is a link to my favorite seed-starting supplies.
When to start seeds indoors
The chart below gives you a start-indoors date for each vegetable so your transplants are ready at the right time for the low desert.
The summer dates might surprise you. By the end of June or in July, I’m at my kitchen table starting fall seeds while it’s too hot to plant much of anything outside. Fall gardening in the low desert begins in the heat of summer, weeks before it feels anything like planting weather. If you wait for fall to feel like fall, you’ve missed the window for many crops.
I try to start at the beginning of each planting window on purpose. It gives the seeds enough time and gives me stronger, larger transplants. A couple of years ago, an intense October heatwave taught me why that matters. My small snapdragon transplants and plugs died. The larger transplants I’d grown out came through fine. A bigger transplant has a bigger root ball. It holds moisture longer and gives you more room for error during a heatwave. A small plug dries out fast.
| Vegetable (days from seed to transplant) | Planting Dates |
|---|---|
| Armenian cucumber* (3-4 weeks) | Start seeds indoors: January 15 – June 15 Plant outside: February 15 – July 15 *does best directly sown in garden Learn how to grow Armenian cucumbers here. |
| Artichoke (8 weeks) | Start seeds indoors: October 15 – January 15 Plant seeds outside: November – Dec. 15th Plant transplants outside: January 15 – March Learn how to grow artichokes here. |
| Arugula (4-6 weeks) | Start seeds indoors: September – January Plant seeds outside: August 15 – January Plant transplants outside: October – February Learn how to grow arugula here. |
| Asparagus (10-12 weeks) | Start seeds indoors: August – November Plant outside: November – February 15 Learn how to grow asparagus here. |
| Beets* (4-6 weeks) | Start seeds indoors: August – January Plant outside: September 15 – February 15 *does best directly sown in garden Learn how to grow beets here. |
| Bok Choy (4-6 weeks) | Start seeds indoors: August 15 – January Plant seeds outside: August 15 – January Plant transplants outside: October – February Learn how to grow bok choy here. |
| Broccoli (4-6 weeks) | Start seeds indoors: August 15 – December Plant seeds outside: August 15 – December Plant transplants outside: October – January Learn how to grow broccoli here. |
| Brussels sprouts (6-8 weeks) | Start seeds indoors: July 15 – October Plant seeds outside: August 15 – November Plant transplants outside: September – November Learn how to grow Brussels sprouts here. |
| Cabbage (4-6 weeks) | Start seeds indoors: August 15 – December Plant seeds outside: August 15 – December Plant transplants outside: October – January Learn how to grow cabbage here. |
| Celery (10-12 weeks) | Start seeds indoors: July – September Plant seeds outside: August 15 – December Plant transplants outside: September 15 – December Learn how to grow celery here. |
| Vegetable (days from seed to transplant) | Planting Dates |
|---|---|
| Cantaloupe* (3-4 weeks) | Start seeds indoors: January 15 – June Plant outside: February 15 – July *does best directly sown Learn how to grow cantaloupe here. |
| Cucamelon (6-8 weeks) | Start seeds indoors: January – March July 15 – August Plant transplants outside: February 15 – April August 15 – September Learn how to grow cucamelons here. |
| Cucumber* (3-4 weeks) | Start seeds indoors: January – March July 15 – August Plant outside: February 15 – April August 15 – September *does best directly sown Learn how to grow cucumbers here. |
| Eggplant (8-10 weeks) | Start seeds indoors: December 15 – January May 1 – June Plant transplants outside: March July 15 – August 15 Learn how to grow eggplant here. |
| Ground cherry (6-8 weeks) | Start seeds indoors: December 15 – January May 15 – June Plant transplants outside: February 15 – March July 15 – August 15 Learn how to grow ground cherries here. |
| Kale (4-6 weeks) | Start seeds indoors: August 15 – December Plant seeds outside: August 15 – December Plant transplants outside: October – January Learn how to grow kale here. |
| Kohlrabi (4-6 weeks) | Start seeds indoors: September 15 – December Plant seeds outside: August 15 – November Plant transplants outside: October 15 – January Learn how to grow kohlrabi here. |
| Leeks (8-12 weeks) | Start seeds indoors: August 15 – November Plant seeds outside: August 15 – October 15 Plant transplants outside: January Learn how to grow leeks here. |
| Lettuce (4-5 weeks) | Start seeds indoors: August 15 – January 15 Plant seeds outside: August 15 – January Plant transplants outside: September 15 – Feb. 15 Learn how to grow lettuce here. |
| Luffa* (3-4 weeks) | Start seeds indoors: January 15 – March 15 July 15 – August 15 Plant outside: Feb 15 – April 15 August 15 – September 15 *does best directly sown Learn how to grow luffa here. |
| Malabar spinach (4-6 weeks) | Start seeds indoors: January 15 – April Plant outside: March – May Learn how to grow Malabar spinach here. |
| Mustard (4-6 weeks) | Start seeds indoors: September – January Plant seeds outside: August 15 – January Plant transplants outside: October – February Learn how to grow mustard greens here. |
| Vegetable (days from seed to transplant) | Planting Dates |
|---|---|
| Onions (8-10 weeks) | Start seeds indoors: October – December 15 Plant seeds outside: October – November Plant transplants outside: December – February 15 Learn how to grow onions here. |
| Peppers (8 weeks) | Start seeds indoors: December 15 – January and May Plant transplants outside: February 15 – March and July Learn how to grow peppers here. |
| Pumpkin* (3-4 weeks) | Start seeds indoors: February and June – July 15 Plant outside: March and July – August 15 *does best directly sown Learn how to grow pumpkin here. |
| Roselle hibiscus (4-6 weeks) | Start seeds indoors: February – April Plant outside: March 15 – May Learn how to grow Roselle hibiscus here. |
| Spinach (4-6 weeks) | Start seeds indoors: August – January Plant outside: September – February 15 *does best directly sown Learn how to grow spinach here. |
| Swiss chard(4-6 weeks) | Start seeds indoors: August 15 – January Plant seeds outside: August 15 – January Plant transplants outside: September 15 – Feb. 15 Learn how to grow Swiss chard here. |
| Summer squash* (3-4 weeks) | Start seeds indoors: January 15 – March 15 July 15 – August 15 Plant outside: February 15 – April 15 August 15 – September 15 *does best directly sown Learn how to grow summer squash here. |
| Tomatillo (6-8 weeks) | Start seeds indoors: December 15 – January May 15 – June Plant transplants outside: February 15 – March July 15 – August 15 *Plant 2 to ensure pollination Learn how to grow tomatillos here. |
| Tomatoes (6-8 weeks) | Start seeds indoors: December 15 – January May 15 – June Plant transplants outside: February 15 – March July 15 – August 15 Learn how to grow tomatoes here. |
| Winter squash* (3-4 weeks) | Start seeds indoors: February and June – July 15 Plant outside: March and July – August 15 *does best directly sown Learn how to grow winter squash here. |
The last step before planting out: hardening off
You’ve done the work to get your seedlings ready. Don’t skip this last step. Hardening off lets them adjust to outdoor conditions a little at a time instead of all at once.
To harden off seedlings, start by setting them outside in a shady spot during the day and bringing them back in at night. Over several days, give them a bit more sun each day. Seedlings that are hardened off gradually settle into the garden far better than ones moved straight from the shelf to full sun. I walk through the whole process in how to harden off seedlings.
FAQs about when to start seeds indoors in the low desert
It depends on the crop. Most cool-season vegetables get started indoors from August through December. Warm-season crops like tomatoes and peppers start indoors in December and January for a spring garden, then again in May and June for a fall planting. I start mine at the front of each window so I have time to grow strong transplants. Use the chart above for the exact dates by vegetable.
Yes. An Arizona garage gets too hot in summer to start seeds well. I start mine indoors where the temperature stays steadier. Some crops, like lettuce and onions, want it even cooler, closer to 60 to 70 degrees, before they’ll sprout.
Root crops and a few others do best sown straight into the garden, because their roots don’t like being disturbed. That includes beans, carrots, beets, radishes, corn, peas, and squash. Garlic and potatoes also go straight into the ground.
You can. July is part of the window for starting tomatoes for a fall harvest. If you’re running behind, tomato transplants are usually available locally in late July and August as a backup.
Bigger is safer when you’re planting into heat. A larger transplant has a bigger root ball that holds moisture longer and gives you more room for error. I’ve watched small plugs die in an October heatwave while my larger transplants came through fine.
Would you like the low-desert planting dates for vegetables, herbs, and flowers in a convenient calendar?
*PLANTING GUIDE: Each month has a planting guide (letter boards) for the vegetables, herbs, and flowers to plant in the low desert of Arizona.
*HARVEST GUIDE: Harvest guides are the harvest photos of what it is possible to harvest each month.
I will plant my seeds outside in the next week. Should I put burlap on top of the soil and then add mulch on top of the burlap or mulch first and then burlap?
Generally you use burlap in place of mulch. If you’re going to use mulch, you don’t need to use burlap.
Hi Angela,
Thank you so much for all of this great info! We don’t get back from a trip until July 10th. Do you think it would be too late to start tomatoes then?
It will probably be fine. I’m having the same issue with summer seed starting this year as well. Luckily Arizona Worm Farm said that they will have tomato starts ready to go in late July or August, so that is also an option. Best of luck to you and enjoy your vacation!
Thank you so much! I wish I would have read this before I planted my seeds in my seed trays. I planted cabbage, kale, and collards so I will follow these directions once they start sprouting. I have them in my Arizona room, but at night I’ll move them inside and then in the mornings I’ll water and put them back in the Arizona room. I know I can do this lol.
Thank you so much! I wish I would have read this before I planted my seeds in my seed trays. I planted cabbage, kale, and collards so I will follow these directions once they start sprouting. I have them in my Arizona room, but at night I’ll move them inside and then in the mornings I’ll water and put them back in the Arizona room. I know I can do this lol.
Thank you for such a helpful list of when to plant seeds. It can be confusing! I have a question on starting the seeds. I have a large light stand in my garage and am hoping to start the seeds out there but am worried about it still being too hot in September. What are the best temperatures to start the seeds in? P.S. I love your calendar!
So glad it’s helpful. It is too hot in the garage during the summer in Arizona to start the seeds. Indoor temps are much better and some crops like lettuce and onions prefer even cooler weather (60-70F) before sprouting.
Angela, this is incredibly helpful! I was really unsure about how long many of the plants should grow indoors and hence when they should be started in order to plant outside at the correct time. Thanks for the chart!
So glad it was helpful. I found myself wondering and figured others had questions about it as well. Thanks for letting me know. Best of luck with your garden.