Managing Crassula helmsii in large marshes surrounding lake, South West England – 18/03/2020 – 03/04/2020

Crassula Helmsii in stagnant water
May 2019

Stagnant/still water, end of lake

The South Eastern end has a large concentration of C. helmsii mostly in aquatic form and some in its terrestrial form. Management was successful to a large degree as it was mostly accessible and visible. However, it was certainly less luxuriant in its growth to May last year (right hand image). This is likely due to the water levels being dropped, but there is also a concern that the autumn/winter leaf litter was still hiding a large amount of C. helmsii. The root and stem structure under leaves and in the mud isn’t always easy to identify as being C. hemsii. We checked thoroughly buts its impossible to say what still lies beneath.

Lowered water level, Crassula Helmsii early Spring
March 2020

The exposed low lying stringy aquatic form was easy to identify whilst water levels were lower and was thoroughly treated. The fairly large amount still in the water had very little growth above the surface and therefore would be impossible to treat using chemicals. It was therefore pulled carefully to the sides.

This was then checked as much as possible for newts etc and left for 6 hours allowing aquatic life to head back into the water. It was then treated. On the second visit 10 days later the C. hemsii looked mostly dead. This was then turned over, checked for green growth (which much of it still had) and treated again.


Moving aquatic form of C. helmsii

Issues were discovered when moving the aquatic form of C. helmsii above the water level. The stems/roots can break whilst relocating it to the edges, therefore causing the ability for C. helmsii to spread. The same should be considered when handling it in mud, it is likely to break the stems/roots if moving larger concentrations. (I don’t believe it could be pulled out by hand without causing this damage.)

The treated C. helmsii is drying out on the banks whilst the chemical treatment is still completing its task. Once checked that treatment has completed, potentially the dense clumps of Crassula should be collected away from the water’s edge and burnt before water levels rise.  In moving dead crassula, it should become obvious if there is any remaining green crassula underneath and care should be taken over not moving it whilst still in the process of treatment.

Southern Marsh

Crassula helmsii in marsh pondMuch of the Crassula helmsii appears in a more succulent terrestrial form across the marsh. However, the larger concentrated areas had the aquatic appearance due to the habitat it was growing as reported below.

Most of the C. helmsii’s larger concentrations were similar amounts as last year, although a couple of areas suggested it had spread to quite a degree. One of the notable areas is a waterlogged pond within the marsh (marked in red on map and pictured right) We had to treat some of the C. helmsii on the surface of the water. However, It’s also a rather deep area of the marsh and a great deal of the plant was submerged. We carefully pulled to the edges to create denser mats above water to treat. We also considered whether waders would be beneficial but concluded that we would in fact create greater damage and therefore cause it to spread.

Crassula Helmsii habitatAnother difference to last years survey is the obvious habit of C. helmsii around the lake. It appears to have spread or it could just be more visible due to the lower water level. As well as the more random patches where Crassula helmsii grows, it particularly likes the conditions directly behind the Reed mace and Iris borders of the lake. I checked the North Marsh for the same pattern and found it was the same. This is not one consistent line by any means, but a pattern nevertheless.

These would be good areas to monitor for the progress of its management.

Crassula helmsii behind reedsCrassula helmsii margins

These areas were easy to treat and could be directed mostly at C. helmsii alone. However there will be some losses of other species in those specific areas, consisting of the moss Calliergonella cuspidata, water horsetails, water mint and a few species of either grass/sedge/rush (as pictured to the right). All these species thrive throughout both marshes mostly unaffected by the presence of Crassula helmsii.

Notable patterns and habits of Crasulla helmsii at this location.

Crassula helmsii terrestrial form1) There was one clear difference in its form, noticeable in front of the bird hide (to the left looking out to the lake). Both last year and this year it remained shorter and more succulent in its terrestrial form. In May/Jun 2019 this was the area it flowered abundantly.

rushes in marsh2) It doesn’t favour the horsetail /rush area East of the South marsh, but it is found around the edges. This can be seen from the Eastern square pontoon looking west beyond the marsh marigolds.


sundew_horsetail_sphagnum3) It doesn’t seem to favour all areas of the marshes and so far it doesn’t appear to dominate areas which are most species rich. Areas of sphagnum hummocks/ bogs appear unaffected. These areas also consist of marsh St Johns wort, water mint, water horsetails and sundew to name a few and partially covered by bog myrtle and Alder.

4) C. helmsii is never found on steep sides of the lake but grows only on the shallow/gentle flat slopes of muddy banks and marsh edges. It has formed concentrated dense patches where water is still or pushes towards a shallow bank.

5) As in above report, It was not found in the water around the Reedmace and Iris in the edges of the lake. However, there was a pattern observed a few meters in from the edge of the lake, forming a line behind the Reedmace and Iris. (Images, page 2)

6) I found it coexists well with the moss Calliergonella cuspidata. From a distance it can look similar and be considered as dense patches of C. helmsii, when it is in fact both species growing together.


Conclusion – including limitations of treating Crassula helmsii at this site

  1. C. helmsii is easier to spray without harming other species in the dense patches where it is dominant. However, it is frequently found less dominant and growing with other species in small areas, therefore treatment causes some losses of native species. These areas are currently contained and not in large areas of species rich habitat or where significant loss would be problematic.
  2. C. helmsii can be spread when traversing by foot whilst treating. Special attention to cleaning of boots was practiced where possible.
  3. An unknown amount of C. helmsii is still aquatic although water levels have been dropped. Moving submerged crassula was extremely problematic. We felt stems/roots were being broken in doing so. Small pieces could float away, creating potential spread. Thankfully the dense submerged areas are in stiller waters where less movement of small pieces is likely to spread throughout the lake.
  4. As above, If waders were used to traverse in submerged areas to lift C. helmsii to above water level, we believe even more damage to stems and roots would be highly likely.
  5. Leaf litter was potentially covering an unknown amount of roots and bare stems in the Eastern concentration. Lifting the leaves exposed roots of unidentifiable species. This may require treatment later in year when more obvious. This may also be the case in the Willow/Alder carr off the southern marsh. Although the small patches surveyed in 2019 were found and treated.
  6. We have been lucky in that no rain has fallen since treatment apart from a very light sprinkling directly after second treatment.
  7. I understand the months of bad weather caused some delay, it was noted that on the second spray, more species were appearing, causing difficulties to not spray young native species that weren’t there before. Any spraying later in the year should be kept to managing small/new colonies of C. helmsii.
  8. Although thorough, It would be foolish to think we managed to find every plant when carrying spraying equipment. When surveying it was noted that some areas had a couple of stems alone. I also noted that where small amounts were mapped previously with a marker, it had sometimes disappeared.
  9. When carefully moving any submerged C. helmsii, check for aquatic life and leave it for a period of time before treating.

Potential further treatment this year

  • It might be worth considering periodic treatments to find any stray plants missed, now that the main concern has been treated.
  • The areas where the dense patches were treated, should be checked for any further treatment required.
  • Monitor the aquatic growth (red areas on map) more may rise to the surface and require treatment. Monitor for any new spread due to the movement in area when treating. (as above report)
  • Remove and burn dense treated patches.
  • Check what appears through leaf litter in South East section for further treatment. It is possible that Mar/Apr is not a good period to assess the extent of C. helmsii.