Marginal Aquatic Plants
When dividing hardy marginals, remember these plants are generally very strong and hearty. There are two basic types with different
growth habits, which affect your repotting method. Some marginals are upright and clumping, while others are horizontal and running.
For the upright, clumping plants – rushes, sedges and umbrella grass – the healthy part(s) you remove should be planted in the center of regular pots with the plant’s crown level the soil’s surface. Use a sharp cutting instrument (I have found the serrated blade of a small saw works very well), and remove onethird to one-half of the original plant. This will make a good sized plant and allow for enough new growth in its new pot.
These plants also benefit from having fertilizer tablets added at this time. Again, place some gravel on top of the soil and position the pot
near the surface to up to 6 inches in depth. Using smooth gravel, such as one to two-inch river rock, is preferable in case the pot tips
over. That way no sharp edges of your gravel will damage your flexible liner or other pond material.
For the plants that have fast-growing horizontal rhizomes, such as irises, cattails, pickerels, and sweet flags, it is helpful to use a wider pot so they don’t “jump” your pot by season’s end. Again, use a sharp cutting tool and, as with the waterlily, place the cut end of the rhizome against the edge of the pot, allowing for the new growth toward the center.
The running types of marginals – water clover, floating heart, bog bean, and water snowflake should also be planted in wider-sized pots
with shallow soil. Again, add fertilizer to these pots, and top off with a layer of smooth gravel. Place near the surface of your pond.
If you find you have too many new plants for your pond after you have divided them, place them, either potted or bare-rooted, in a shallow
tub outdoors with good sunlight. Depending on the amount of water in the tub, crush two to three large fertilizer tablets and add them
to the water.
Even though dividing plants can be a messy job, think of all the benefits your plants and pond receive from your efforts!
Note: For most water plants, repotting should take place when there are signs of new growth. It is recommended that lotuses be divided somewhat earlier, before they show signs of growth due to their tender growing tips.
Some marginals, such as pickerel and thalia, benefit from having some initial growth first, so their repotting might be delayed until the
end of May. To receive as many blooms as possible from iris, they are best divided in the summer or early fall so they can use their stored energy to bloom early the following spring.
August 2005 Newsletter