Drescription

Grow them in pots, planters, or straight in your garden and petunias will reward you with big, bold flowers that just don’t quit. But if you want these colorful plants to keep on blooming from spring through fall, it’s important to water them right and just when they need it.

Whether you’re new to growing petunias or just want to take your plants to the next level, this petunia watering guide is packed with expert tips on how and when to water petunias for peak flowering and healthier plants.

Meet the Expert

Cynthia Haynes, PhD. is a professor of horticulture at the Iowa State University.

Eva Ward oversees the annual greenhouse team at Ward’s Nursery.

Signs Your Petunias Need Watering

Petunias wilt quickly if they don’t get enough water, and drop leaves, turn brown, and die back if their soil gets super dry. But you don’t need to wait for your plants to show signs of stress to know it’s time to water them: Just take a good hard look at the soil they’re growing in.

“Petunias don’t like to stay wet for long periods, so check the soil first before watering,” says horticulture professor Cynthia Haynes. “Just scratch around the top inch of soil with your fingers to see if it’s dry, or lift smaller containers to check their weight. Then, water when the top inch of soil dries out or the container feels light.”

Want more gardening tips? Sign up for our free gardening newsletter for our best growing tips, troubleshooting hacks, and more!

When Is the Best Time to Water Petunias?

Like other plants, petunias absorb water best if you water them in the morning or in the evening a little before sunset. If you water petunias when the sun is high overhead, it can increase the amount of water that’s lost to evaporation and make it harder for your plants to absorb the water they need.

That said, if your plants look stressed, it's better to water them right away than wait until morning.

“Petunias are heavy drinkers and don’t recover well if the soil gets too dried out,” says plant expert Eva Ward. “Don’t wait for petunias to droop—water stress opens plants up to pests and many other problems.”

How Often to Water Your Petunias

Petunias should be watered often enough to keep their soil evenly moist, but not so frequently that their roots get waterlogged and start to rot. Exactly how often to water petunias can vary depending on the season, the size of your plants, the temperature, and the pots your petunias are growing in.

“Watering frequency could be every 2 to 3 days, or daily if it’s a large plant in a hanging basket in full sun,” says Ward. “For larger patio containers, always keep the soil surface moist and use a lightweight mulch like buckwheat hulls to prevent evaporation.”

Petunias growing in the garden will typically require less water than potted plants and may only need to be watered once a week. But this watering frequency can also vary, so always test the soil with your finger before you water.

The Right Way to Water Your Petunias

There’s no one-size-fits-all watering schedule for petunias. But in general, you’ll need to water petunias less in spring and more when temperatures rise and the plants fill out in summer. Being flexible with watering and following these simple tips will help you avoid underwatering or overwatering your plants and encourage petunias to flower more.

Water Deeply

“When watering, water deeply,” advises Ward. “And make sure the soil is fully moist and that excess water drains out of planter drainage holes.”

The best way to do this is to water low and slow with your hose or a drip irrigation system. Deep, slow watering allows water to penetrate well into the soil around petunia roots and can keep gardens and planters from drying out too quickly.

Keep Leaves Dry

Like other plants, petunias can develop mildew issues if their leaves stay wet too long. To avoid this, water your plants in the morning and direct water to the soil line to keep it from splashing up on your plant's leaves.

Don’t Overdo It

Don’t be tempted to water petunias if their soil still feels wet. Overwatering is a surefire way to stress out your plants and cause petunias to wilt, yellow, or die from rot.

Add Fertilizer

“You’ll get the best flowers if you use a blossom booster liquid fertilizer with every other watering all season," Ward says. "Or if you prefer a slow-release granular blossom booster, scratch that into the soil surface around petunias in mid-June, mid-July, and mid-August.”

Applying fertilizer when the soil is already moist helps petunias absorb it faster and can prevent fertilizer burn.