Overview: 

Zinnias are one of our summer staples that thrive in the summer heat, even here in Phoenix. We love planting them because they are easy to start from seed, and offer so much color. Traditionally zinnias were tall flower reaching 3-4’ in height. These varieties would either need to be staked and supported or they would flop over in a rainstorm.

New varieties are on the market that give the same zinnia flowers, on compact plants that only get 12-18” tall. These varieties are perfect for anyone that has a balcony garden, container garden, or simply wants to enjoy zinnias without having to support them.

Starting seeds:

Starting zinnia seeds is relatively easy. You can direct seed them into containers or the ground when nightly temperatures are consistently in the 50’s. Here in Phoenix that is typically towards the end of march. We wait until night time temperatures are high because that is when zinnias are actively growing. They do not like cooler temperatures and could be prone to root rot if they are too wet and cold.

If you have a bird or animal problem you can start them inside and transplant them into your beds. sow them 1/4” deep. Check out our seed starting guide for more tips and tricks.

We direct sow zinnias in containers here. We planted them about 6" apart with two seeds in each hole that we will thin out to a single plant. We like to have 3 plants in out planters that range from 12-16" in diameter. 

Pro tip: If birds or animals are an issue, use a mesh trashcan and place it upside down on top of the seedlings. This will help protect them from critters, while allowing sunlight and water to penetrate the plants. We will take it off once the seedlings become more established and true leafs are formed. We source  these from amazon, Walmart, target, or even dollar tree. 

Spacing: 

9-12” for in ground planting 6-9" for containers. If you live in a more humid climate, consider spacing zinnias further apart. Powdery mildew can be a problem in wet climates, so ample airflow helps prevent the spread.

Sun: 

Full sun, 6-8+ hours per day.

Water:

Zinnias like consistent moisture. Make sure they dry out a little bit in between waterings.

Fertilizer:

We typically liquid feed zinnias every two to three weeks during their growing season. They do not need a lot of fertilizer, but some keeps them pushing out blooms. Find our favorite fertilizer here.

Potential issues:

The only issues I have seen people run into while growing zinnias is powdery mildew. This is a fungal disease that is mainly caused by high humidity. We are so dry here in Phoenix that its typically not a huge issue. In places where it is an issue, we recommend spacing out your plants more so they can get airflow. 20 -30 percent more spacing should help. Succession planting more frequently may also help, as younger plants can tolerate powder mildew better than an older succession.

Succession plant:

Yes, I definitely recommend succession planting. I’m going to be the first to say that i’m by no means the best at succession planting zinnias but you can plant these flowers almost all summer long. I typically plant three secessions of them because our growing season is so long. We do a Spring planting (April) early summer (early June) and mid summer (July) for beautiful zinnias all summer.