No, you should not water zinnias every day in most cases. These flowers do best with deep soaking once or twice per week. Too much water hurts your zinnias more than too little water ever will.
So how often to water zinnias for the best results? Give them about one inch of water per week. During hot dry spells above 90°F (32°C), bump that up to two waterings per week. During cooler rainy weeks, you can skip watering and your zinnias won't mind at all. They handle dry spells far better than soggy roots.
I learned this the hard way during my first season growing zinnias. I watered them every single morning thinking more was better. By mid-July the lower stems turned soft and brown. Three plants died from root rot before I figured out what went wrong. The next year I switched to deep watering twice a week. In my experience the same variety grew twice as tall with zero rot. That one change fixed everything for me.
The reason deep watering works better ties back to how your roots grow. When you water a little bit every day, your roots stay near the surface. They never need to push deeper because you keep the top soil wet. Deep watering forces your roots to chase moisture down through the ground. This builds a root system 12-18 inches deep that anchors your plant and reaches nutrients that surface roots can't find.
UMN Extension puts it in clear terms. Water your zinnias only when the top 1-2 inches of soil are dry. They note that your zinnias handle drier soil better than wet soil. This lines up with what you see in the garden. Zinnias came from wildflowers in the dry scrublands of Mexico. They carry that drought toughness in their genes. Treating them like water-loving plants is the fastest way to kill them.
A good zinnia watering schedule works like this. Check your soil every two to three days by pushing your finger 2 inches deep near each plant base. If the soil feels dry at that depth, give your bed a full deep soak at ground level. If it still feels damp, leave it alone and check again the next day. Water in the early morning so your leaves dry before evening. This cuts down on fungal disease in your beds.
During heat waves above 95°F (35°C), your container zinnias may need daily water since pots dry out much faster than garden beds. Your in-ground zinnias can handle the heat with their deep roots and two solid waterings per week. Add a layer of mulch around the base to hold moisture longer. You'll water even less with mulch on your side.
The goal for your zinnias is always moist soil at root depth and dry leaves on top. Get this balance right and your plants will thrive through the hottest months without you standing over them with a hose every morning. Save yourself the time and your zinnias the stress by watering deep and watering less. Your flowers will look better for it all season long.
Read the full article: Zinnia Flowers: How to Grow and Care
