How to grow carpet plants without injected CO2

Everyone loves carpets. However, as smaller plants growing on the substrate, they have less access to light and are more delicate than larger, more robust plants. With a little specialist attention, a variety of carpets can be grown with high success rates in a low-tech aquarium.

3 challenges to overcome

Growing a carpet without the help of CO2 injection is like trying to build muscle with limited access to good protein, or swimming without goggles. It can be done, but success depends heavily on overcoming 3 challenges:

LIGHT

Carpets need decent lighting to reach them as they lie at the furthest point from the tank, on the substrate, but many low-tech tanks choose to use low lighting for fear of algae. Many of the more attractive types of carpet plants grow better with more light.

CO2

In nature, many aquatic plant species grow in CO2 rich environments, but here we want a "low tech" setup that does not use CO2 injection to replicate such a condition. 

ACCLIMATION

The most difficult stage of growing a carpet is at the beginning. There are several factors that contribute to transition stress in newly planted plants; if you have purchased them in an emersed form they need to transition to submerged growth forms, if they have come from different water parameters they need to reprogramme their enzymes to suit the current tank environment. The chances of success are maximised if transition stress is reduced.

The Possibilities

By following the guidelines below you should be able to grow Dwarf Hairy Grass Carpet (DHG), Monte Carlo (MC), Microsword (Lileopsis species) and Marsilea species without CO2 injection. Glossostigma may need more light. The HC Cuba plant is difficult to grow without CO2 and should not be attempted unless you have a lot of time and plants to waste, but this approach will massively increase your chances.

Best species that can be grown without CO2:

Rating Easy:

• Lilaeopsis brasiliensis (Microsword) 
• Marsilea crenata/hirsuta
• Cryptocoryne parva [doesn't spread; need to manually propagated]
• Hemianthus glomeratus (Pearlweed) [A stem plant that creeps, needs to be pruned low]

Rating Moderate:

• Micranthemum monte carlo (MC)
• Eleocharis acicularis (Dwarf hairgrass)

Rating difficult:

• Hemianthus callitrichoides 'cuba' (HC/dwarf baby tears) [best with CO2]
• Glossostigma elatinoides (Glosso) [Needs a lot of light]
• Utricularia gramminifolia (UG) [Needs stable, matured tank]

Examples of low tech planted aquariums with green carpets:

This tank has Lilaeopsis brasiliensis as a carpet. Microsword grows slowly and takes months to fill in without CO2 injection.

The dwarf hair grass carpet above in the above 3 gallon tank was grown completely from scratch and took around 3 months to fill in.

The 2Hr 4 Step Approach

Shallow Tank: 12" or less

A shallower tank (we recommend 12 inches or less) allows for more illumination at substrate level without an expensive lighting system and allows for a less steep light gradient. Shallower tanks also tend to have a higher soil to water volume and better gas exchange. They are easier to manage overall; easier to access, which helps with maintenance.

The guide in the algae section of this site outlines how to maintain an algae-free tank without the use of heavy chemicals.

Stronger Light

In your light choice, aim for a PAR value of above 50 Umols at substrate level. we use close to 100.
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To find out how to read a PAR table, go here. For example, if you are using a tank that is 12 inches deep with 2 inches of substrate, the relevant depth is 12-2 = 10 inches. This takes you into what many sources call "high light" territory. However, there is an increased risk of algae growth if the tank parameters are not well controlled. We recommend you read the guide to avoiding algae - something you will need to master if you are using high light levels in a low-tech tank.

Using stronger light greatly increases the chances of success with carpet plants in low-tech tanks.

Here we use a 23watt CFL desklamp to grow dwarf hairgrass in a low tech tank. The adjustability of the desk lamp's height allows me to cast more or less light into the tank.

Use Soil Substrate

There is an abundance of substrate choices, as detailed here. To grow a carpet in a low-tech environment, use topsoil or garden soil without additives. A well-balanced loamy soil - roughly equal parts clay, silt, sand and organic matter with some peat will do. The organic content of the soil should not exceed 20%. Soils that are too unstable will cause more stability problems due to excessive decomposition. If you are using very organic-rich soil, use about an inch or less. Commercial aquasoils are a good option that takes the guesswork out and are much easier and less messy to use, but they cost a lot more.

Soil decomposition provides low levels of carbon. It will not completely make up for the lack of CO2 injection, but it will provide enough to grow light carpets. Carpets also root better in soil.

Only a thin layer of soil is needed to grow carpet plants. A 1 or 2 inch layer of soil followed by a thin cap of 1/3 or 1/2 inch works well. You can use a thicker cap if you are worried about disturbing the base of the soil when replanting.

In this example, a thin sand cap is used over a raw soil base.

In this low tech example above,  HC is grown using an aquasoil cap over raw garden soil. Aquasoilactually makes a great cap; it stays on top of raw soil easily, whereas heavier sand sometimes sink if the substrate is disturbed.

Transition / acclimatization

Many plants fail to grow, not because of a lack of growth conditions, but because they cannot withstand the transition process when transferred from another aquarium with very different water parameters.

In CO2-injected planted aquariums, the rapid increase in growth allows plants to adapt quickly. In non-CO2-injected planted tanks, plants have to make the difficult adjustment without the help of sufficient CO2. There are 2 key parts to reducing the transition shock:

Step 1: perform full pre-cycling

This means completing the ammonia cycle for the tank and allowing the tank bacteria colonies to mature, usually by running the tank filter and allowing the water to settle for 2-3 weeks. This process can be accelerated to about 1 week if a starter culture is used. This step is often ignored by impatient aquarists at their peril. Ammonia easily burns young and delicate plants.

Volatile organic compounds also trigger algae growth. Allowing the tank time to mature biologically will reduce algae problems. This is an important point, especially when starting with higher light levels.

For detailed steps on how to cycle a tank, click here.

Step 2: go local

Getting plants from the same water parameters as the tank environment greatly reduces transition stress and melting. Alkalinity (KH values) has a greater impact than other variables; staying within a 3 dKH range is very safe.

If you want to avoid the hassle of actually measuring water parameters, get plants from your state or province: there is a good chance that the water parameters will be very similar to your tap water. Good suppliers should know where their plants are grown / come from. If you buy plants that have been shipped from far away, there is a significant risk that the water parameters will be very different, increasing the likelihood of transition shock/death.

Finally, how you plant matters

Carpets should be spread thinly over the substrate rather than planted in large clumps. (Commercial YouTube channels give many negative examples of this by planting in huge clumps).

Planting in smaller clumps allows each individual clump to get better light, nutrients and air flow, and the plants will root better compared to starting in a crowded spot. Individual plantlets also root better.

This is HC Cuba plant in a 5 gallon high tech tank. Planting technique is similar regardless of CO2 usage.

For list of best carpeting plants for planted tank, click here.