Almost every aquarium plant sold in Australia was grown out of water, and most buyers have no idea. It changes what pests arrive with the plant, what algae comes attached, and whether it thrives or melts in the first fortnight. Knowing which form you are buying is the difference between a scape that fills in and one that quietly dissolves.
What the terms mean
Emersed grown plants are grown out of the water, with their roots wet and their leaves in humid air. Submersed grown plants are grown fully underwater.
The terminology is used loosely in the hobby. Emersed is sometimes written as emerged. Submersed appears as immersed or submerged. They all refer to the same two states.
Most aquarium plants are amphibious, meaning they can grow either way. Commercial nurseries grow the overwhelming majority emersed, because plants grow faster in air where CO2 is freely available, take up less space, and ship far better.
Telling them apart
Some species look almost identical in both forms. Others are barely recognisable as the same plant.
Ludwigia arcuata, Ludwigia palustris and Bacopa monnieri, left to right in both images. Bacopa looks much the same either way. The two Ludwigia species are almost unrecognisable.
The most reliable visual cue is the leaf surface. Emersed leaves carry a waxy cuticle to stop them drying out in air, so they look glossy and feel slightly thick and firm. Submersed leaves have no need for it, so they are thinner, softer and often more translucent.
How plants are sold in Australia
A good online seller will tell you which form their plants are in. In shops you will usually see two formats, and neither is quite what it appears.
Plants in display tanks
Believe it or not, plants sitting underwater in a shop tank are not necessarily submersed grown. Most are bought from wholesalers in emersed form and placed in tanks purely for display, which means they are emersed plants part way through converting. Some genuinely are submersed grown. Asking a staff member is your best bet.
Tissue culture tubs
The small round plastic containers hold tissue culture plants, grown in sterile conditions on nutrient gel. They are guaranteed free of pests, snails and algae, which makes them excellent for a new scape or a shrimp tank. They are emersed grown, and they are expensive in quantity.
Why it matters
Pests
Submersed grown plants can carry hitchhikers: snails and snail eggs, hydra, planaria and occasionally damselfly larvae. Snails are mostly harmless and can be useful grazers, though unsightly in numbers. Hydra and planaria are a different matter and can be lethal to shrimp.
These pests survive shipping comfortably. If they arrive in your aquarium they will establish, and removing an entrenched planaria population is far harder than preventing one.
Emersed and tissue culture plants do not carry them at all, which is the single strongest argument for buying emersed if you keep shrimp.
Algae
Every aquarium carries some algae, so submersed grown plants will arrive with some attached. In a balanced aquarium that is a non issue.
The risk is a plant arriving heavily covered. A significant algae load introduced all at once can outcompete your plants for light and nutrients before your tank has a chance to respond, which is why supplier choice matters more for submersed plants than for anything else you buy.
If something does take hold, our algae guides cover identifying and correcting each of the common types.
Transition
So why not simply buy emersed every time? Because an emersed plant has to convert once it goes underwater, and that conversion is where plants are lost.
The plant must shed its waxy cuticle, rebuild its leaves to draw CO2 and nutrients from water instead of air, and adjust its entire growth structure. Some species barely notice. Others, Cryptocoryne in particular, melt back to the rhizome before returning.
During conversion, new submersed leaves develop while old emersed leaves remain. Those old leaves cannot survive underwater and will die regardless. If you leave them to decay in the tank they add to the organic load and can trigger an algae outbreak, which is how a plant purchase turns into an algae problem.
How to transition emersed plants
This is the part that decides whether emersed plants work for you, and most of it is straightforward.
Conversion is demanding, and an aquarium still finding its feet is the worst environment for it. A tank with an established biofilter and settled parameters gives the plant its best chance.
Carbon is the single biggest factor in how smoothly conversion goes. In air, plants have effectively unlimited CO2. Underwater they suddenly do not, and that shortfall is what a converting plant feels first.
Pressurised CO2 makes conversion dramatically easier, and the AquaLabs CO2 range covers everything needed to run it. Without injection, AquaLabs Carbon Aid supplies bioavailable carbon and ferrous iron directly to the water column, which supports plants through the transition.
A rich aquasoil makes conversion noticeably easier, because the plant can draw on the substrate while its submersed leaves are still developing. In an inert substrate such as sand or gravel, root tabs do the same job.
AquaLabs Enrich Root Tabs place nutrients directly at the root zone, which matters most for heavy root feeders such as Cryptocoryne, swords and Vallisneria during conversion.
Strong light over plants that cannot yet photosynthesise efficiently underwater feeds algae rather than the plant. Six hours at moderate intensity is plenty while they convert. Increase once you see new submersed growth.
Wait until there is meaningful new submersed growth, then cut the old emersed leaves away. Remove them from the aquarium rather than letting them break down in it.
Do not strip everything on day one. Until new leaves appear, those old ones are still feeding the plant, and removing them early is a common way to kill something that would otherwise have made it.
Cryptocoryne in particular will often drop every leaf and look dead. Provided the rhizome is firm, leave it alone. It will regrow from the base in submersed form, usually within a few weeks.
Which should you buy?
Worth clearing up a point that often gets muddled: a high tech aquarium with CO2 and aquasoil makes conversion easy, but emersed plants still take longer to fill in than submersed ones, because they spend their first weeks rebuilding rather than growing. You are trading early speed for a clean, pest free start.
A low tech aquarium faces the opposite trade. Submersed plants settle in immediately and need no conversion, which suits a tank without CO2, but you accept whatever arrives attached to them.
What not to do
Common mistakes
- Stripping all the emersed leaves at planting. They are still supporting the plant until new growth appears. Wait.
- Leaving dead emersed leaves to rot in the tank. They will decay and add organics, which is a reliable way to trigger algae during an already delicate period.
- Adding submersed plants straight into a shrimp tank. Quarantine or dip them first. Planaria and hydra are far easier to keep out than to remove.
- Giving up on a melted Crypt. Check the rhizome. If it is firm, the plant is alive and will come back.
- Assuming shop tank plants are submersed grown. Most are emersed plants in display tanks, part way through converting. Ask.
The short version
- Emersed means grown in air, submersed means grown underwater. Most commercial plants are emersed
- Emersed leaves are waxy, glossy and firm. Submersed leaves are thin, soft and often translucent
- Tissue culture tubs are emersed grown and completely free of pests and algae
- Plants in shop display tanks are usually emersed plants mid conversion, not submersed grown
- Submersed plants can carry snails, hydra and planaria, and hydra and planaria are lethal to shrimp
- Emersed plants must convert underwater, which is where plants are lost
- Carbon matters most during conversion, whether from CO2 injection or a liquid carbon source
- Keep light modest until new submersed growth appears
- Trim old emersed leaves only once new growth is established, and remove them from the tank
- Melted Cryptocoryne with a firm rhizome is not dead and will return
Neither form is better. Emersed buys you a clean start and costs you a few weeks. Submersed buys you an instant scape and costs you a quarantine. Knowing which you are holding is what lets you plan for it.