Short Interval Cyclic Flooding Affects Growth and Physiology of Three Native Shrub Taxa

Plant species adapted to wet conditions are likely candidates for rain gardens due to their ability to withstand alternating wet and dry periods. On 16 June 2008, rooted stem cuttings [0.25 L (2.25 in)] of Viburnum nudum L. ‘Winterthur’ (possumhaw), Ilex glabra (L.) A. Gray. ‘Shamrock’ (inkberry holly), and Itea virginica L. ‘Henry’s Garnet’ (sweetspire) were potted in 2.5 L (trade gal) containers and arranged in a randomized complete block design with 5 blocks in a greenhouse in Auburn, AL. Beginning on 21 July 2008, plants were flooded to substrate level for 0 (non-flooded control), 3, or 7 days and then allowed to drain for one week before the same flood cycle was repeated. Photosynthesis (Ps) rates were measured for V. nudum ‘Winterthur’ and I. virginica ‘Henry’s Garnet’ during flooding and draining cycles in plants flooded for 3 and 7 days with concurrent measurement of Ps of non-flooded control plants. On 10 Oct. 2008, the experiment was terminated. Non-flooded plants of I. virginica ‘Henry’s Garnet’ and I. glabra ‘Shamrock’ had higher growth indices (GI) [(height + widest width + width perpendicular to widest width)/3] than plants flooded for 3 or 7 days. Shoot dry weight (SDW) of I. glabra ‘Shamrock’ was lower when plants were flooded for 7 days than when flooded for 0 or 3 days. SDW for I. virginica ‘Henry’s Garnet’ was higher in non-flooded plants than plants flooded for 3 or 7 days. I. virginica ‘Henry’s Garnet’ root dry weight (RDW) was higher in non-flooded plants and plants flooded for 3 days, than in plants flooded for 7 days. RDW for I. glabra ‘Shamrock’ was highest in non-flooded plants, followed by plants flooded for 3 or 7 days. RDW, SDW, and GI for V. nudum ‘Winterthur’ were not different among treatments. I. virginica ‘Henry’s Garnet’ Ps rates were higher during flooding than during draining in both flooding treatments, and Ps rates were higher in control plants than in flooded plants. V. nudum ‘Winterthur’ Ps rates were similar in non-flooded and flooded plants indicating its ability to tolerate flooding and maintain rates of Ps. Although growth and Ps of I. virginica ‘Henry’s Garnet’ and I. glabra ‘Shamrock’ were generally lower in flooded plants than non-flooded plants, all taxa maintained visual quality and continued to grow which suggests they all would be acceptable choices for use in rain gardens.