this plant occurs sporadically around the garden as a single stalk but one that gets quite woody if is older. I have looked online but can’t seem to find out what it is.
Also can roses that are watered by an automatic watering systems suffer root rot if its set too frequently?
The plant in the picture you sent is very similar to Knotweed but the leaf arrangement appears to be opposite as opposed to alternate leaf arrangement which is seen in the Knotweed.
Your plant appears to be a Katsura seedling. Katsura leaves are heart-shaped and have an “opposite” leaf arrangement. Perhaps you or someone in your neighbourhood has a Katsura and it has been self-seeding. Katsura trees flower in March or April and produce pods with winged seeds (similar to maple trees). which can be pollinated by wind.
Further information about the Katsura can be found on the North Carolina State University website:
http://plants.ces.ncsu.edu/plants/cercidiphyllulm-japonicum
With respect to your question about roses suffering from root rot due to overwatering, there are many factors which influence how often roses need to be watered. This includes your soil type, plant size & type, environmental conditions, where the rose is planted etc.
The American Rose Society provides an article “How Often Should I water my Roses” which will provide you with more information about watering. https://www.rose.org/