Can Knock Out Roses Be Watered From the Top?

Problems

• Watering from the top of the plants wets the leaves as well as the roots. Since knock out roses absorb most of their water from the roots, top watering serves little to no practical function for the plant. Leaves that stay wet even for less than a day are vulnerable to fungal infections. Fungal spores are usually airborne, though they can splash onto the undersides of leaves when falling water hits ground infested with rose-leaf-infecting diseases.

Disease Resistance

• Knock out roses have better disease resistance than most other rose varieties and cultivars, but this does not make them invulnerable to disease. The longer and more often the top growth of knock out roses is wet, the higher the chance for fungal disease to take hold and do greater damage. While knock out roses can survive well through many disease attacks, constant top watering will only help the disease flourish and will reduce the chances that the knock out rose will be able to overcome the disease and survive.

Rain

• Rain is technically top-watering, and it, too, will encourage disease. If the knock out rose is watered under the topgrowth by the gardener, that presents fewer chances for diseases to insinuate themselves and take hold. Rain also has far more nutrients and far fewer toxins in it than household water, making it less stressful of a bath for knock out roses than tap water.

Considerations

• If the only way to water the knock out rose is by top-watering, it should be done in the early morning, allowing plenty of opportunity for the water to evaporate before damage can be done. Top watering during midday in the summer focuses the hot sunlight and burns the leaves. Watering at any time of year before or during nightfall means the water will stay on the leaves longer, encouraging disease problems.