As a zinnia, our vibrant blooms and lush foliage are a testament to a healthy root system, and nothing is more critical to our roots than consistent moisture. The intense heat and sun of a US summer can quickly parch the soil, leaving us stressed, stunted, and vulnerable. The right mulch acts as a protective blanket for our root zone, and from our perspective, some choices are far superior to others.
For us, a 2 to 3-inch layer of shredded bark or wood chips is the ideal partner for summer survival. This organic mulch is exceptional at slowing the evaporation of precious water from the soil after you irrigate. It also moderates soil temperature, keeping our roots comfortably cool even during afternoon heatwaves. As it slowly decomposes over time, it improves soil structure and adds beneficial organic matter, which further enhances the soil's water-holding capacity. It's important that this mulch is not piled directly against our stems, as this can create overly moist conditions that lead to rot.
Straw (not hay, which contains weed seeds) and pine straw (pine needles) are also excellent choices. They are lightweight, allow for good air circulation, and form a loose, fluffy layer that is incredibly effective at retaining soil moisture. Pine straw is particularly beneficial for us as it decomposes slowly and helps to slightly acidify the soil, which we tolerate very well. These mulches are easy to apply around our base without smothering us and are often readily available.
While shredded leaves or dried grass clippings are organic and will eventually benefit the soil, they must be used with caution. If applied too thickly or when wet, they can mat down into a dense, impermeable layer. This can block water and air from reaching our roots and can create a humid environment that promotes fungal diseases like powdery mildew on our lower leaves. If you use these, ensure the grass clippings are dried first and that leaves are well-shredded, and apply in thin layers.
Please avoid using inorganic mulches like rocks or gravel around us. These materials absorb the intense summer heat during the day and then radiate it back towards our stems and the soil surface at night. This literally bakes our root zone, drastically increasing water loss and soil temperature, leading to severe heat stress. Rubber mulch similarly absorbs and radiates heat and does not improve the soil in any way, making the environment around our roots far harsher.
For mulch to work best, you must first ensure we are well-watered. Apply the mulch to moist, warm soil in early summer, once the soil has had a chance to heat up but before the peak drought stress hits. A layer 2-3 inches deep is perfect; any thicker can suffocate us, and any thinner won't adequately suppress weeds or retain moisture. Please keep the mulch a few inches away from the base of our stems to prevent rot and allow for air circulation.
