Studies in outdoor, circular pools have shown that one shoot tip of hydrilla (Hydrilla verticillata Royle) produced as much plant dry weight during a 16-week period as 16 tips planted under the same conditions. Dry weight of plants 16 weeks after planting was as high as 1,561 times that of the shoot tips planted. Tubers were present within 8 weeks after planting the tips; higher numbers of these vegetative propagules were associated with the higher number of tips planted. Plants under a photoperiod of 11.5 h or less produced more tubers than those exposed to 12 h or more of light.

Subterranean turions (tubers) of hydrilla lose viability when desiccated. Experimental data showed that freshly collected tubers had a moisture content between 50 and 60% and more than 90% viability. When desiccated, there was an approximate 2% increase in tuber mortality with each percent decline in moisture content. However under field conditions, the tuber bank within the exposed sediments of a northern Texas reservoir showed no decline in number or tuber viability throughout a 12-mo continuous drawdown. Apparently, the buried tubers were never subject to sufficient dessication to damage them. Finally, an experimental pond with an extensive hydrilla tuber bank was manipulated through six flood/drawdown cycles to determine the effects of short-term drawdowns on tuber survival and quiescence. Initially, the pond had a tuber bank of about 676 and 305 tubers m−2 in the shallow and deep zones, respectively. Although the tuber number was reduced to fewer than 15 to 30 tubers m−2 by these repetitive drawdowns, hydrilla tubers were not eradicated from the pond.