Aquarium carpet plants and the dry start method

Picking a carpet plant: with or without CO₂

Carpet plants stay low and spread sideways. Whether they take off depends first on light and CO₂, and only then on substrate and fertilizer.

• CO₂ and strong light: Hemianthus callitrichoides 'Cuba' (dwarf baby tears) and Glossostigma elatinoides give the finest, densest carpet but rarely survive long without injected CO₂,
• Micranthemum 'Monte Carlo' grows best with CO₂ but tolerates lower light and no injection – slower and less compact,
• no CO₂: Marsilea hirsuta is undemanding, just slow to spread in a low-tech tank; Cryptocoryne parva grows without CO₂ but needs more light than other crypts and must not be shaded, and it takes a long time to fill in,
• dwarf hairgrass (Eleocharis) can work in a low-tech tank, but it wants somewhat more light and fills in more slowly.

A carpet needs enough light at the bottom of the tank, or it grows upward instead of sideways. In a low-tech tank, though, keep the photoperiod to 6–8 hours and do not turn the light up just to speed growth – without CO₂ the plants cannot use the extra light, and algae will.

Planting tissue culture

• tissue culture cups are the easiest start: take the plant out, rinse the growth medium off under running water and split it into small plugs, down to single plantlets if you can,
• plant with tweezers and bury most of each plug – shallow plugs float up when the tank is filled,
• space the plugs a few centimeters (an inch or so) apart; the more plants per area, the less room algae get,
• carpets need a substrate to root into: aquasoil feeds them for the first months, while sand or gravel needs root tabs.

The dry start method, step by step

In a dry start the plants grow emersed in damp substrate under a cover, and you only flood the tank once the carpet has rooted. Meanwhile the roots knit into the substrate and mosses attach to the hardscape undisturbed. It suits species that can grow out of water: HC 'Cuba', Monte Carlo, hairgrass and mosses. Fully aquatic plants such as Vallisneria will not grow emersed.

• mist the substrate until it is damp all the way through but not waterlogged – no puddles on the surface and no visible water line at the front,
• leave a small unplanted spot at the front so you can see whether water collects, and siphon out any excess with airline tubing,
• seal the top tightly with cling film; fogged glass and droplets on the film show the humidity is holding,
• mist whenever the substrate starts drying – plants closest to the light dry out first,
• air the tank once a day, no longer than half an hour,
• run the light longer than you would underwater, most often around 10–12 hours a day (guides range from 8 to 14),
• no fertilizer and no CO₂ yet – the substrate supplies the nutrients.

Stem plants gain nothing from a dry start: they can dry out, and after flooding they transition back to submersed growth more slowly. Epiphytes such as anubias or java fern only cope if the humidity stays very high; otherwise they dry out. It is safer to add both just before flooding.

How long? Plan on roughly four to six weeks, but go by the plants rather than the calendar: flood once they are firmly rooted and sending runners sideways.

Mold during a dry start

Mold is what most often ruins a dry start, and it usually comes from a substrate kept too wet and too little airing. White fuzzy patches are mold: mist less, air the tank more and pick out any dead leaves straight away.

Hydrogen peroxide spray is sometimes suggested, but guides disagree on the dilution and on whether it harms the plants, so no dose is given here. If mold covers a large area, it is safer to flood the tank early – with filter, heater and any CO₂ ready – or to start the dry phase again.

Flooding and the first weeks

Before flooding, install the filter and any CO₂, and plant the stems and epiphytes. Fill slowly and break the flow with a plate, a colander or airline tubing so the water does not wash out plants or substrate.

From that moment the tank behaves like a new one. Aquasoil releases ammonia once it is underwater, so test NH₄ and NO₂, do water changes as you would while cycling and add livestock only after both read zero for several days.

Drop the photoperiod to six hours and build up to seven or eight over the next few weeks. If you run CO₂, start it on the first day underwater.

Some emersed leaves may melt after flooding while the plant grows submersed ones, more so without CO₂. As long as new growth keeps coming, this is normal.

Keeping the carpet healthy

• trimming: dense carpets such as Glossostigma, Monte Carlo and HC 'Cuba' need regular, hard trims close to the substrate with curved scissors; net out the clippings so they do not rot,
• carpet lifting and floating: when it gets too thick, the top layer shades the bottom, which dies off and lets whole mats tear loose – regular trimming prevents it; replant anything that floats,
• an old carpet thinning from below: if it keeps peeling up despite regular trimming, pull out the affected patch and replant the healthy plugs,
• melting after planting: emersed-grown leaves die back while new submersed ones form; if new shoots keep appearing, change nothing,
• older leaves turning yellow: often a nutrient shortage, nitrogen in particular; root tabs help a carpet, especially once aquasoil runs low after a few months – but check CO₂ and light first,
• algae in the carpet: densely planted ground leaves less room for it; shorten the photoperiod and remove it by hand, as in any new tank.

What to log and why

Log the planting day as the setup date and the flooding day as a note. The tank's day count runs from planting, but count cycling from the day you flood. During the dry start, a custom routine with a reminder keeps misting on track. Photos from the same angle after one week, two weeks and a month show whether the carpet is really filling in. And when it starts yellowing or lifting, the journal shows when you last trimmed, fertilized or changed the light.