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When to Start Seeds Indoors: A Seed-Starting Guide for Low-Desert Vegetables

By: Angela Judd | July 10, 2020

Knowing which seeds to start indoors and when to start seeds indoors in Arizona can be confusing. In this article, you will learn which crops are best direct-sown with seeds in the garden and which crops can be started indoors to get a jump on the growing season.

I’ve included a seed-starting guide for low-desert Arizona gardeners to help you know when to start the seeds inside. This chart (at the end of the article) includes dates for beginning sowing seeds indoors so they will be ready for transplanting at the right time. Low desert includes elevations below 3500 ft in the Southwest, such as the Phoenix and Tucson metro areas.

If you are unsure how to start seeds indoors, this article shares 10 steps for successfully starting seeds indoors.

When to Start Seeds Indoors A Seed-Starting Guide for Low-Desert Vegetables

When you learn how to start seeds indoors and start them at the correct time, you can have the advantages of growing from seed combined with the advantages of adding transplants directly into your garden.

What We’ll Cover:

1. When to use seeds
2. When to use transplants
3. Crops that are best to direct-sow in the garden
4. Which seeds to sow indoors and transplant outside in the low desert of Arizona
5. When to start seeds indoors
6. Harden off seedlings before transplanting them in your Arizona garden

6 Tips for Growing Vegetables from Seed in Arizona

1. When to use seeds

Starting garden vegetables from seed has several advantages. Seeds are often much less expensive than purchased transplants. There is also a greater variety of options when starting from seeds. When you grow from seed, you aren’t limited to planting what your local nursery or big box store has in stock.

Arguably, the biggest benefit is that plants grown from seeds can be planted at the optimal planting time for your location. Planting at the correct time is crucial for success.

Are you wondering which seeds to use? For trusted varieties that grow well season after season, visit my favorite seeds.

Wondering which seeds to start in June? This month’s planting guide has all the details.

2. When to use transplants

Planting transplants in the garden has advantages as well.

Long-season crops like tomatoes and peppers need the head start that planting a transplant provides.
Transplants are convenient, easy to use, and yield more predictable results than starting from seed.
Planting transplants give you a harvest sooner.
Transplants are also more resistant to damage from pests and insects than tiny seedlings.

3. Crops that are best to direct-sow in the garden

Some crops do best when directly seeded into the garden rather than starting seeds indoors and planting transplants. The roots of these crops do best when left to grow undisturbed. Just click on the name of the vegetables to go to the seeds.

Best direct sown:

Crops like garlic and potatoes aren’t planted from seeds but from actual garlic cloves and sprouted potatoes, so they also do best when directly sown into the garden.

A young boy in a blue striped shirt kneels next to a garden bed, planting seeds while wondering when to start seeds indoors in Arizona for the best results.

4. Which seeds to sow indoors and transplant outside in the low desert of Arizona

Vegetables with a long growing season are often started indoors and then transplanted outside for the best chance of success.

Here is a link to my favorite seed-starting supplies.

Long growing-season vegetables grown best from transplant:

Still, other seeds are slow to germinate and do best when started under optimal growing conditions inside, such as:

Several small potted seedlings, including peppers and tomatoes, sit in black trays on a brown surface. Blue plant labels are placed in some pots, ideal for tracking when to start seeds indoors in Arizona. Watermark: “GROWINGINTHEGARDEN.COM.”.

Although some crops have definite preferences about being sown in the garden or indoors, others will grow fine when planted either way.

Vegetables that can be started from seed or transplant include:

A hand places seeds into small holes in dark, moist soil mixed with wood chips, illustrating the careful process of planting and knowing when to start seeds indoors in Arizona for a thriving garden bed.

5. When to start seeds indoors

When you learn how to start seeds indoors in Arizona and start them at the correct time, you can have the advantages of growing from seed combined with the advantages of adding transplants directly into your garden at the best time.

Seedlings in small pots and trays are arranged on three wire shelves under grow lights, complete with colored labels. This indoor setup is ideal for learning when to start seeds indoors in Arizona and helps organize each plants progress.

Use the following chart to determine when to start seeds indoors for your low-desert Arizona garden so they will be ready to plant at the correct time for your growing season.

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 artichoke here.
Arugula (4-6 weeks)	Start seeds indoors: September – January Plant seeds outside: August 15 – January Plant transplants outside: October – February
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 (4-6 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.

A hand holds a small plant with green leaves and exposed roots, ready to be transplanted into soil in a garden bed. Drip irrigation tubes and mulch are visible in the background—a perfect scene for those learning when to start seeds indoors in Arizona.

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 (3-4 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.

Seedlings with green leaves growing in small black plastic pots, arranged in rows on a tray near a window with natural light—perfect inspiration if youre wondering when to start seeds indoors in Arizona. The soil in the pots is visible.

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.

6. Harden off seedlings before transplanting them in your Arizona garden

Several small tomato plants in black pots are arranged on a wooden table outdoors, with bright sunlight casting shadows and highlighting the healthy green foliage—perfect for those wondering when to start seeds indoors in Arizona.

You’ve worked so hard to get your seedlings ready to plant in the garden. Don’t forget this last step. It is very important to “harden off” seedlings before planting them in the garden. This allows them to adjust to the different conditions outside gradually rather than all at once.

To “harden off” seedlings, begin by taking them outside to a shady location during the day and bringing them inside at night. For a few days, expose them to a little bit more sunlight each day. Plants that are “hardened off” correctly adjust better when planted out in the garden.

If you’re looking for tools, soil amendments, or seed-starting gear check out my carefully curated gardening supplies and tools page. It includes everything I rely on in the garden.