7 Tips for Growing Colorful Spring Annuals in Arizona

Growing spring annuals in Arizona comes down to timing: plant cool-season color by February, add heat lovers like zinnias and portulaca in March and April, and protect everything from heat after mid-April. These seven tips cover soil, water, feeding and heat.

Key takeaways

• Plant cool-season annuals such as snapdragons, petunias, alyssum and pansies from October through February, because highs usually reach the 90s by mid to late April.
• Set out zinnias, portulaca and vinca from March into May, once nights stay above about 50°F and the soil has warmed.
• Loosen the bed 8 to 12 inches deep, mix in 2 to 3 inches of compost, and top it with about 2 inches of mulch.
• Water deeply, and check the soil 2 inches down before watering again; March beds often need water every 2 to 3 days.
• Deadhead every few days and use 30 to 40 percent shade cloth in the afternoon to stretch cool-season color into May.

When should I plant spring annuals in Arizona?

Plant cool-season annuals from October through February and warm-season annuals from March through May. Snapdragons, pansies, petunias and alyssum want nights in the 40s and highs in the 60s and 70s, while zinnias, portulaca and vinca want warm soil and nights that stay above about 50°F.

Fall planting gives the longest show because roots establish before winter. Late winter planting still works, but those plants get a short run before highs reach the 90s in April. Frost can show up in the East Valley through February, so keep frost cloth handy for any warm-season annuals set out early. Timing decides the whole season. Our gardening calendars show planting windows month by month.

Which spring annuals handle Queen Creek weather best?

Snapdragons, petunias, alyssum and pansies give the best cool-season color, and zinnias, portulaca and vinca carry the beds once it turns hot. Snapdragons (Antirrhinum majus) send up dense flower spikes and fade as highs settle into the 90s. Petunias (Petunia hybrids) bloom heavily in mild weather and slow down in heat. Alyssum (Lobularia maritima) forms a low, fragrant edging, and pansies (Viola × wittrockiana) are the earliest and least heat-tolerant of the group.

For warm weather, zinnias (Zinnia elegans) bloom steadily in full sun with regular water. Portulaca (Portulaca grandiflora) tolerates hot, dry spots and needs little care once established. Vinca (Catharanthus roseus) loves summer heat but sulks in cold soil. These are varieties we commonly carry in our annual flowers and foliage department, and availability changes week to week and season to season.

What are the seven steps to a full spring bed?

Seven steps cover the whole job: match the plant to the date, prepare the soil, plant in cool hours, water deeply, mulch, feed, and deadhead. Order matters.

1. Match the plant to the date. Use the window in the table above, and choose cool-season annuals before March or warm-season annuals after it.
2. Prepare the bed. Loosen the soil 8 to 12 inches deep and mix 2 to 3 inches of compost into the top 6 to 8 inches. If water pools or the shovel hits a hard, pale layer, you have found caliche, so break through it with a digging bar or build a raised bed 10 to 12 inches deep.
3. Plant in the evening or on an overcast day. Dig each hole slightly wider than the root ball and set the crown level with the soil, because planting too deep invites crown rot.
4. Water in slowly. A slow soak settles soil around the roots and removes air pockets.
5. Mulch about 2 inches deep. Keep the mulch 1 to 2 inches back from the stems.
6. Feed on a schedule. Mix a balanced slow-release fertilizer into the bed at planting, then use a liquid feed every 3 to 4 weeks at the label rate.
7. Deadhead every few days. Pinch off spent blooms so plants keep making flowers instead of seed.

How often should I water spring annuals?

Water when the soil 2 inches down feels barely damp, which in March usually works out to every 2 to 3 days for in-ground beds. As highs climb into the 90s in April, plan on watering every day or two. Roots follow moisture.

Aim for a deep soak that wets the soil about 6 inches down, because shallow daily sprinkles keep roots near the surface where heat reaches them first. Drip irrigation delivers water at the roots and keeps leaves dry, which cuts down on fungal problems. If you hand-water, do it in the morning so foliage dries before midday. Our irrigation water is hard, so an occasional long soak helps flush salts below the root zone.

Why are my spring annuals turning yellow?

Yellow new leaves with green veins usually point to iron chlorosis, which happens when alkaline soil, often with a pH between 7.5 and 8.5, locks up iron the plant needs. Treat it with an iron chelate labeled for high-pH soils, applied at the label rate, and expect new growth to green up over a couple of weeks.

Overwatering looks similar. Soggy soil suffocates roots, and the plant yellows even when iron is available. Check drainage before you reach for a product. Even yellowing across older leaves points to low nitrogen, which a regular liquid feed corrects. Compost worked into the bed at planting also improves drainage and gives roots a better start in our alkaline ground.

How do I keep spring annuals blooming into May?

Afternoon shade, regular deadheading and a replacement plan stretch the color by a few weeks, although cool-season annuals fade once highs stay in the 90s. A 30 to 40 percent shade cloth over the bed from about 11am to 4pm cuts heat stress on snapdragons, pansies and alyssum. It is not pretty. It works.

Deadheading pays off most on petunias and zinnias. Pinch or snip spent flowers just above a leaf set every few days. A short walk through the bed twice a week keeps up with it.

When cool-season plants finally quit, pull them and replant with zinnias, portulaca or vinca within the same week so bare soil does not bake. Vinca prefers warm soil, so it fares better planted in April or May than in March.

Can I grow spring annuals in pots?

Yes, and pots give you control over soil and sun. Fill them with potting mix rather than garden soil, which compacts and drains poorly in a container. A pot 12 inches wide or larger holds moisture better than a small one, and glazed or plastic pots lose water more slowly than unglazed clay.

A classic combination puts a snapdragon in the center, petunias around it and alyssum spilling over the edge. Check pots daily from March, since a container in full sun can need water twice a day once highs pass 95°F. Browse pottery and planters if you need a bigger pot to slow that drying. When the heat arrives, refresh the top few inches of mix with compost and replant with heat lovers instead of discarding it.

What mistakes cost the most spring color?

Five mistakes cost the most color: late planting of cool-season annuals, skipped soil prep, shallow watering, buried crowns and mulch piled against stems. Each one is easy to avoid once you know it.

• Planting snapdragons or pansies in April, when highs in the 90s leave them only a few weeks of bloom. Plant them early.
• Setting transplants into unamended, compacted soil or on top of caliche, so roots stay shallow and water pools.
• Watering lightly every day instead of soaking the bed and letting the top 2 inches dry slightly between waterings.
• Planting with the crown below the soil line, which holds moisture against the stem and invites rot.
• Stacking mulch against stems, which keeps the base of the plant constantly damp.

If you want to see these steps in person, check our classes and events page for what is currently scheduled.

Frequently asked questions

Can I grow spring annuals from seed in Arizona?

Yes, with zinnias and portulaca as the easiest. Sow them directly in the bed from March into April once the soil has warmed, and keep the surface damp until seedlings emerge. Cool-season annuals are harder from seed. Most gardeners buy transplants for those because the window is short.

Is it too late to plant cool-season annuals in April?

Yes, for most of them, because highs in the 90s shorten the bloom period to a few weeks. Pansies fade first. Zinnias, portulaca and vinca handle April planting well and, with regular water, keep blooming into the summer heat, so choose those instead of cool-season color.

How far apart should I space spring annuals?

Most bedding annuals go 6 to 12 inches apart, and the plant tag gives the right spacing for each variety. Crowded plants look full for a few weeks, then hold moisture in their leaves, lose air circulation and become more prone to fungal problems and heat stress. Read the tag.

Do spring annuals need full sun?

Most do best in full sun, though pansies, violas and alyssum keep their color noticeably longer when they get shade after about 2pm once April warms up. Zinnias and portulaca take all-day sun. Petunias fall in between and bloom best with at least 6 hours of direct light.

Should I fertilize annuals in pots differently?

Yes, containers need feeding more often because frequent watering flushes nutrients through the pot. Mix slow-release fertilizer into the potting mix at planting, then add a liquid feed every 2 to 3 weeks at the label rate while the plants are blooming and the weather is mild. Water before you feed.

Are spring annuals worth planting in the low desert?

Spring annuals pay off when you want fast color in a bed, a pot or along a walkway and you are willing to water regularly and replace plants as the heat arrives. Skip them if you want color that needs no replanting and little water; flowering desert shrubs and perennials suit that better. For everyone else, a plan with cool-season color first and heat-tolerant annuals second keeps beds full into summer. Stop by our nursery in Queen Creek and we will help you choose for your yard.