Our Adventure With Victoria 2004
Our lowest survival was of V. amazonica in Tanks 3 and 4. It did fine in the stable temperatures of Tanks 1 and 2 but also did extremely well in the shallow preformed Tank 5. Because it was black plastic, the water temperature rose rapidly on sunny days and retained more heat at night than would have been generated by its small heater. We think it was the high daytime temperature that allowed amazonica to thrive there.
V. cruziana did not do well in Tanks 1 and 2 after the first few floating leaves. It appeared that the difference between warm water and cold air at night caused melted spots on the pads. They did very well in Tanks 3 and 4 where there was more of a drop in water temperature at night. We had no losses of cruziana in 6" or 8" pots in any tanks.
We also had no losses of 'Adventure' or 'Longwood Hybrid', most of which were in duneside Tank 4. As an additional experiment, we put same-age sibling 'Longwood Hybrids' in Tank 4 and Reflection. Though we almost lost the one in Reflection, it survived but not in as good condition as the one in Tank 4. This indicated to us that even the (average) 3-4 degrees additional heat in Tank 4 made a difference.
The more heat/less sun compared with less sun/more heat question was answered. Results were more or less the same, with the exception of amazonica. Duneside plants were more battered by wind and spotting from the cold but most survived in spite of it.
There are two other factors that may have affected the survival, or lack, of the V. amazonicas in Tank 4. This spring we learned that the size and number of holes in the pots makes a difference - the more the better. It isn't necessarily that roots benefit from escaping into soil on the bottom. Even some plants on racks (where the roots couldn't reach any soil) did far better than others in pots with smaller and fewer holes.
We also learned more recently that refreshing the peat in the bottom of the pots after 6 weeks to two months greatly enhanced plant health, especially amazonica's. As mentioned elsewhere, we don't know for sure which properties of peat are so beneficial to Victoria - just that they are. If we had known to refresh the peat over the winter, it's possible more amazonicas could have survived in the colder Tank 4.
These experiments have raised a new question that we will be looking at over the next months -- do some of these older stalled plants increase in size more slowly than younger plants? In 2003, Rich Sacher observed that an over-wintered 'Longwood Hybrid' grew very slowly compared with a spring-started plant in equal conditions at New Orleans Botanical Garden.
We are currently growing out six over-wintered plants. As we write this in mid-May, two are increasing in size as rapidly as we would expect and two are increasing very slowly. It's hard to tell yet with two that have been more recently planted. We have such a long growing season that we can wait to see if the slow plants eventually catch up. One of the slow plants puts up new leaves every third day and the other only about one a week, so speed of growth doesn't seem to make a difference..