Can Downoi and Large Ammannia Grow Together?

Downoi and Large Ammannia share a workable water window around 22 to 28 °C, pH 6 to 7.5, and 4 to 12 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: Downoi does best with moderate light and recommended added CO2, while Large Ammannia does best with high light and recommended added CO2.

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

Downoi reaches about 10 cm tall by 10 cm wide, while Large Ammannia reaches about 50 cm tall by 15 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.

Both are typically rooted in substrate with nutrient-rich substrate preferred and feed mainly as mixed feeders. The method is simple, but it also means the same planting zone can feel crowded if they are placed too close together.

Mature size is not the main thing working against this pairing, so normal maintenance is usually enough to keep the scape readable.

Downoi brings moderate growth, moderate maintenance, and intermediate difficulty. Large Ammannia brings moderate 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, so spacing matters more than usual; 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.