Can Large Ammannia and Red Milfoil Grow Together?

Large Ammannia and Red Milfoil share a workable water window around 22 to 28 °C, pH 6 to 7, and 4 to 10 dGH.

Both plants are comfortable in freshwater, so salinity is not a meaningful obstacle.

Both prefer moderate flow, so circulation can be planned as one steady pattern.

Their light and CO2 needs are close enough for one routine: Large Ammannia does best with high light and recommended added CO2, while Red Milfoil does best with high light and required added CO2.

Both plants naturally lean toward the midground and background, which is why spacing, pruning, and final mature size matter more than they do in a more staggered planting mix.

Large Ammannia reaches about 50 cm tall by 15 cm wide, while Red Milfoil reaches about 60 cm tall by 8 cm wide. Use those mature sizes for the layout, not the small nursery portions you bring home.

Shade is the biggest layout risk. If the taller or denser plant gets ahead, the other one can slowly decline even when water and nutrients still look fine.

Large Ammannia is typically rooted in substrate with nutrient-rich substrate preferred and feeds mainly as a mixed feeder. Red Milfoil is typically rooted in substrate with nutrient-rich substrate preferred and feeds mainly as a water column feeder. That difference can make the pairing easier to arrange than two plants fighting for the exact same root or attachment zone.

They can share the space, but the scape will stay cleaner if you leave more room than the labels alone might suggest.

Large Ammannia brings moderate growth, high maintenance, and advanced difficulty. Red Milfoil brings fast growth, high maintenance, and advanced difficulty. If one grows much faster, trim that plant before it starts making the other look like the problem.

The practical watch-outs are that both plants tend to work in the midground and background, so spacing matters more than usual; and that you will want to leave more room than usual for mature spread and routine thinning; and that shade becomes a real risk here, especially once the taller or broader plant settles in.

The strongest reasons to try the mix are that they share a workable temperature window around 22 to 28 °C; and that their flow preferences sit close enough to tune one layout around both plants.

Use this pairing when you are willing to manage the scape, not when you want a plant-and-forget combination. Start with more spacing than you think you need, then adjust once both plants show their real growth pace.

The simple success test is whether both plants still look healthy after the faster grower has been trimmed several times. If one keeps declining after routine care, the layout is probably asking too much of it.