Buy both plants, plant them side by side, and the winner will surprise you: the plant that carpets fastest with CO2 is not the plant that fills in most reliably without it. Pick the wrong species for your setup and you will wait months staring at bare substrate.
Both are genuine foreground plants and far easier than demanding HC Cuba, but they spread differently, want different light and carbon, and forgive different mistakes.
Direct answer: With injected CO2, good light, and rich substrate, Monte Carlo carpets faster — 4 to 8 weeks against roughly 6 to 10 weeks for Staurogyne repens at the same density. Without CO2 the verdict flips: Staurogyne repens is safer and steadier, while Monte Carlo slows to 2 to 4 months and often stays thin.
The verdict, by tank type
In a CO2-injected tank at 30 to 60 PAR, Monte Carlo is the clear speed winner. Its runners race sideways, each node roots down, and small round leaves close gaps fast. Expect visible spread within two weeks and a closed carpet in 4 to 8 weeks if you plant densely and keep parameters stable.
In a low-tech tank, Staurogyne repens leads on a different measure: it actually gets there. Monte Carlo survives without CO2, but growth slows sharply, the carpet stays sparse, and algae often colonises gaps first. Staurogyne repens grows slowly too, but keeps pushing side shoots and rarely melts when conditions wobble. At 10 to 16 weeks it usually looks better than Monte Carlo of the same age — because it never stopped.
Monte Carlo: how it spreads
Monte Carlo (Micranthemum tweediei) spreads by horizontal runners that root at the nodes, forming a flat mat just 2 to 5 cm tall.
Plant it in small portions, not big mats. Split a tissue-culture cup or pot into portions of a few stems, rinse off any gel, and push each portion in with tweezers, 2 to 3 cm apart. Large clumps trap debris, shade their bases, and float up in sheets once they start pearling. Small portions root faster and knit together sooner.
Monte Carlo wants light at the substrate above all else. With CO2, 30 to 50 PAR gives a dense carpet; without it, often 100 PAR or more is needed to stay low instead of leggy. It also wants rich substrate: aquasoil gives the best start, and root tabs help once soil ages past 6 to 12 months. See the 2Hr Aquarist guide to growing Monte Carlo before planting.
Staurogyne repens: how it spreads
Staurogyne repens, from the Rio Cristalino in Brazil, carpets differently. Left alone it grows as short stems 5 to 10 cm tall. Cut the tallest upright shoots and it sends horizontal, creeping shoots from the base. Trimming every few weeks is what turns a clump into a carpet.
That mechanism makes it more forgiving. Plant stems in small groups with space between them, give moderate light, and they root firmly — thick stems are rarely uprooted by fish and shrimp, unlike Monte Carlo runners. It grows in aquasoil, capped soil, and even plain gravel if nutrients reach the roots, tolerates 20 to 28 °C and pH 6.0 to 7.5, and does not require CO2.
Be honest about the result: a Staurogyne carpet is not a putting green. Even well-trimmed it stays bushier and taller than Monte Carlo — a low hedge, not a lawn — and in low light it grows more upright still. For a flat Iwagumi foreground, Monte Carlo is better; around rocks and wood, Staurogyne repens is better.
Head-to-head comparison
| Trait | Monte Carlo | Staurogyne repens |
|---|---|---|
| Carpet height | 2 to 5 cm, flat lawn | 5 to 10 cm, bushy hedge |
| Spread method | Horizontal runners, rooting nodes | Creeping stems after topping |
| With CO2 | 4 to 8 weeks | 6 to 10 weeks |
| Without CO2 | 2 to 4 months, often thin | 10 to 16 weeks, steadier |
| Light need | 30 to 60 PAR with CO2; much higher without | Moderate; tighter with more light |
| Trimming load | Mow once anchored, then regularly | Top upright shoots every few weeks |
Planting for speed, whichever you pick
Four habits beat any species advantage. Plant densely, at 2 to 3 cm spacing, not one pot and hope. Plant small, dividing cups into the smallest portions tweezers can handle. Feed from day one: rich substrate, an 8-hour photoperiod to start, and a complete liquid fertiliser once cycled.
Fourth, hold conditions steady for the first month. Both plants melt when parameters swing — spiking ammonia, doubled light, or CO2 running out mid-week costs more time than any species choice saves. Siphon debris off the young carpet weekly.
Which should you choose?
Choose Monte Carlo if you run CO2, want a flat lawn-like foreground, and will plant in small portions and wait for anchoring before trimming. It rewards good technique with the fastest, lowest carpet of the two.
Choose Staurogyne repens if you run low-tech, keep fish that nose around the substrate, or want a foreground that doubles as a midground transition. It will not give you a putting green, but it will still be there after a wobble that would have thinned Monte Carlo out. Still torn? Plant both in separate zones, with a stone border between them.
Frequently asked questions
Can Monte Carlo and Staurogyne repens grow together?
Yes, in separate zones, with a gap or stone border between them — Monte Carlo runners spread into neighbouring patches and are hard to separate once mixed.
Does Staurogyne repens need CO2 to carpet?
No. It carpets without CO2, though slower and taller. CO2 improves density, but is not a requirement as it nearly is for Monte Carlo.
Why is my Monte Carlo growing upwards instead of spreading?
Usually foreground light is too low, or portions were planted in clumps that shade themselves. Raise the light, split clumps, and trim only once runners are anchored.
How often should I trim a carpet?
Monte Carlo: mow every 2 to 4 weeks once established in high-tech tanks, less often low-tech. Staurogyne repens: top every few weeks, whenever upright shoots shade the base. Remove trimmings promptly.