Understanding Terrarium Substrates: Updated

We often think of substrates purely in the context of meeting physiological needs - but in reality - they must also meet the psychological needs of the species if stress is to be avoided (wild Rhinoclemmys pulcherrima on a leaf litter substrate in Costa Rica). Photo: Andy Highfield

Along with heating and lighting systems, the choice of substrate in tortoise pens and terraria often causes a great deal of confusion to keepers. Some substrates are excellent, others can be positively lethal. In this article we help you to choose a safe and appropriate substrate, and show you how to avoid those that could kill your tortoise.

There is one thing that a tortoise remains in extremely close contact with from the moment it hatches: the ground. This plays an extremely important role in many aspects of a tortoise's life. It is, however, often overlooked and under-estimated in importance by many keepers. Let’s take a look at why this is so critical, and how we can learn to understand the reasons for this. Lizard ecologist F. Harvey Pough (1992) put this very succinctly:

“In their natural environments, most amphibians and reptiles spend their time at the ground surface, under leaf litter, or in burrows. As a result, they are exposed to microclimates (especially humidities and rates of air movement) that are very different from those perceived by large animals, like humans. Even desert species spend much of their time in burrows or buried in loose sand"

One important factor to recognise is that different types of substrate retain different levels of moisture. Clay type soils and loamy forest type substrates hold far more moisture than do sandy, desert substrates for example. The drainage factor between these different classes of substrate is entirely dissimilar. This in itself has a profound effect upon creatures that are, at best, ever only a few inches away from the surface – and in many cases are completely surrounded by substrate. It is therefore common to see cases of ‘shell-rot’ and respiratory disease in arid-habitat species that have been kept on moist substrates, and dehydration in rain forest habitat species that have been kept on dry, desert type substrates.

Wild female Testudo graeca - Souss Valley, Morocco. Note the extremely dry, stony, and sandy substrate. This is entirely typical of the area.

In years past, for example, many people assumed that grassy lawns were a suitable substrate for Mediterranean tortoises – this is rarely the case. Lawns are actually fairly moist, and cases of shell-rot (a common name for ulcerative cutaneous infections) on the plastron are very often seen in tortoises maintained in this way. Some access to a grassy grazing area is excellent for certain species (Leopard and Sulcata tortoises, for example), but a drier area must also be provided.

Many species need to be able to burrow or to excavate shallow ‘scrapes’, and the substrate, and depth of substrate, used within their enclosure should permit this. These burrows and scrapes are vital microclimates – and where tortoises are deprived of these facilities a whole train of important self-regulatory functions is disrupted. One of the most common results, in arid-habitat species, is the formation of bladder stones due to constant, chronic dehydration (see our other article that discusses links between the environment and the formation of bladder stones in tortoises).

Tortoises frequently bury themselves, either fully or partially, in substrate. This is entirely natural behaviour and pays important roles in regulating water balance and activity cycles. It also provides a safe retreat if temperatures are too high or too low. Here, a mixed soft sand and topsoil substrate is employed.

Tortoises maintained on flat surfaces where burrowing is not possible lose fluids via evaporation and respiration very quickly, their core body temperatures vary much more widely and more rapidly, and they tend to be more active. This last property is not necessarily advantageous to long-term heath, as the main increase in activity is seen in feeding. Animals reared in these conditions therefore tend to grow faster and hence are far more susceptible to developing mineral and trace element deficiencies, especially those implicated in MBD, or metabolic bone disease. See this separate in-depth article for more on that subject: "Unnaturally High Growth rates in Tortoises: Causes and Consequences"

It would be a mistake to believe, however, that microclimates were all that we need to consider. Thermoregulation and temperature stability are also greatly affected by the substrate that tortoises’ experience. In nature, the substrate is typically infinite in mass. Even in quite harsh environments it is offers relative stability (not necessarily directly at the surface, but certainly below it). Tortoises and other reptiles use these properties extensively in their own thermoregulatory behaviour. The degree to which they allow body contact with the substrate, for example, may allow either a positive or negative heat flow to occur. Some species gain most of their heat via basking; others gain a substantial proportion by contact with warm substrates. Some species do both.

A wild Testudo graeca buried into its natural substrate.

One area where substrate mass and temperature stability is especially important is in brumation (hibernation) and also in aestivation. As we all know from basic physics lessons in school, the smaller an object’s mass, the more rapidly it will respond to external changes in temperature. In simple terms, a 2 cm square block of stone will heat up and cool down much more rapidly than one of 20 cm square. This is especially critical for hatchlings and juveniles, as being small, they respond very quickly to external temperature variations. To provide much greater temperature stability to (brumating) hibernating juveniles, then, we can provide a deep tray of earthen substrate into which they can burrow. Surrounded by this mass, their ‘thermal inertia’ is greatly increased. We explore this aspect in a separate article: "Brumation (Hibernation) of Juvenile Tortoises"

Pet shops routinely sell all kinds of ‘special’ substrates that are touted as ‘ideal’ for use with tortoises and turtles. In our experience this is not the case – we would not use of recommend any of these ‘commercial’ substrates ourselves.

Pet stores want your money – and expensive consumables that you will need to buy repeatedly return a very healthy profit. The drawback is that they are rarely healthy or safe for your animals. There are problems associated with all of them, in our experience, however these are by far the most problematic:

Calci-Sand

Very prone to clumping. Can cause eye irritation. This product has been reported to be implicated in numerous cases of gut impaction. We encountered one such case only recently. The tortoise died. We do not recommend use of this material under any circumstances. The tortoises (C. sulcata) shown below were acutely dehydrated after being kept on this material in a reptile store's display vivarium.

Juvenile African Spurred tortoises in a store display: lethargic, dehydrated and on a Calci-sand substrate.

Fibre-based substrates

Often based upon coconut and similar fibres. Can be very dusty when dry. May be ingested. Dehydrating. Fails to provide any thermal advantages. Also, most fibre substrates are an ideal culture base for mould when moist.

An unsuitable coco-coir substrate in a tiny, unsuitable vivarium: the sad fate of many tortoises sold as pets.

One popular fibre-based substrate is coco-coir. While this can be used in tropical terraria, it is categorically not recommended for arid habitat species. We recently ran some tests on this product: "Coco Coir Substrates for Testudo Species: Myth Busters Episode 10"

Alfalfa substrates (rabbit ‘pellets’)

Dehydrating. Has frequently been associated with fungal eye and respiratory infections. Cencentrated protein content that leads to excess rates of growth if consumed. Because it is a) The substrate and b) Is highly likely to be eaten too it will be heavily contaminated by faeces and urine. We see very high rates of contagious and infectious diseases and parasite issues in tortoises where this is used. We recommend avoiding this product.

Juvenile C. sulcata (African Spurred tortoises) on an alfalfa 'pellet' substrate. They are clearly ill, stressed and dehydrated.

Cedar or Pine chips/shavings

Highly toxic when heated, emits noxious fumes. Serious risk of impaction if ingested. Avoid!

Hemp

Although heavily promoted by pet shops, this material has been associated with SEVERE INJURIES and DEATH. The material is primarily manufactured as bedding for horses, but its use with small animals has been growing. Unfortunately, along with this growth in use we have received a considerable number of reports of serious injuries caused by sharp 'splinters'. We decided to obtain some hemp that was being sold for tortoise use and investigate further. The potential for harm was immediately evident. There were numerous pieces with extremely sharp ends and of sufficient strength to cause deep penetrative injuries. The reports we have suggest that eye injuries, injuries to the cloaca and tail, and in males to the penis are the most common.

Hemp sold as substrate. This contains numerous hard, sharp 'spikes' that have been directly responsible for numerous serious injuries and deaths. It is totally unsuitable and is extremely dangerous.

We have also heard of such pieces becoming embedded in the tissue of the throat and mouth, the nares (nose) and at least two cases where it is suspected that death resulted from ingestion and a recent case where this was proven beyond doubt. As a result of our examination, we conclude that we cannot recommend this material. In our opinion, the presence of such very hard, sharp splinters represents an unacceptable danger to tortoises.

It entirely fails to provide adequate microclimates, and we are also aware of a case where a heat lamp caused it to catch fire killing the tortoise. We would urge all members currently using hemp substrates to reconsider and to change to something more suitable.

Bark chippings/mulch

Use with extreme care. An ideal base for fruit flies, mites and similar parasites. Often fatal if ingested. Some bark chippings may include pine or cedar, both of which are toxic. Check carefully before use. Orchid and Cypress bark chippings can be used successfully with some moist habitat tropical species, however.

Beech (hardwood) chips

No tortoise anywhere on earth lives on a substrate resembling this. It is completely artificial and is very dangerous if ingested as well as being a substantial fire hazard. It provides zero microclimate possibilities. Avoid.

Hardwood and mixed hemp pieces sold as "suitable for tortoises" by a pet retailer.

A young Leopard tortoise (Stigmochelys pardalis) being kept in a highly restricted and unsuitable enclosed vivarium with wood-chip substrate. It has already developed severe deformities and is demonstrating stressed behaviours. See "Indoor Accommodation for Tortoises: A Practical Guide" on why such housing is not recommended.

Newspaper or paper towels

Fails to provide any microclimate opportunities whatever. Flammable – use with care near heat sources. Several fires have resulted from paper substrates that have been ignited by heating devices or basking lamps.

Hygiene

Organic substrates, if not changed often enough, can rapidly accumulate very high

levels of bacterial and fungal pathogens that will contribute to disease (Gardner and

Oberdorster, 2005). The smaller the floor space, the more often the soiled substrate will need to be changed.

A recommended approach to substrates

The substrate that we have found to be the most effective and safest by far for Mediterranean and similar arid and semi-arid species consists of a standard topsoil base mixed with varying amounts of soft (play) sand. This needs to be of sufficient depth, about 50mm or 2 inches is recommended as an absolute minimum even for small juveniles. Ideally, aim to have a substrate at least as deep as the hight of the tortoise. Deeper if possible.

Increase the proportion of sand for very arid habitat species (our Testudo kleinmanni have a 30/70 loam/sand mix, for example). Decrease the sand for more humid habitat species, to say 60/40 loam to sand for a Kinixys (Hingeback) tortoises or American box turtles (Terrapene sp.), for example, and mix in some fresh sphagnum moss, leaf litter mulch and similar moisture retaining additives.

Some species, such as this American box turtle (Terrapene carolina triunguis) require higher moisture content substrates. Always carefully study the precise needs of the species involved when considering which substrates to use. Females also require an adequate depth of substrate to allow for safe nesting.

• Be careful when buying topsoil. Some contains fertilisers or similar additives. Some contains perlite or other moisture enhancing additives. Avoid these.

  
  

• Some also now contains 'composted' waste. Be careful. This can include glass, plastic and metal shards. Avoid those that say they include a 'composted' element.

• Check carefully. You want 'simple' topsoil. No additives. No composted waste.

In many cases it can be easier to simply dig some from your own garden.

With sand, we always used 'soft' or 'playsand'. This most closely resembles the sand found in most natural habitats and tends to be screened for safety.

The precise 'blend' between topsoil and sand will be variable. Experiment, Find out what works best in your own circumstances.

You can also add some gravel, (no, they will not 'choke' on it - see photos of the natural habitats). Again, this will require some experimentation and adjustment to find the ideal blend in your circumstances.

A wild Testudo graeca graeca in Spain on its natural substrate.

Some time varying the proportions may be required depending upon exactly what type of loam and sand you use, but in general terms, this substrate is cheap, easy to clean, offers excellent thermal ‘cushioning’, provides excellent microclimate opportunities, and has proved consistently safe with every appropriate species we have kept. It should be changed every few weeks. Interim maintenance can be carried out by ‘surface scraping’ from time to time as necessary.

Some concerns have been raised regarding the possibility of ingestion when sandy substrates are used. We have not found this to be a problem despite many years of intensive use. We placed ceramic tiles in feeding areas, and utilised a very high fibre diet. This assists any ingested material to ‘pass through’ safely. Do not forget that many of these species live on an almost pure sand substrate for their entire lives in nature!! This is another topic where baseless myths and nonsense proliferates online see. See our in-depth article on sandy substrates in nature.

Finally, disregard the baseless and unscientific claims you will encounter on 'tortoise forums' and on poorly educated social media groups. Ask yourself a simple question. What does this species live on in the wild? That is your best possible guide to what is also safe and correct in captivity. Try to replicate that and you will not go wrong.

A wild Testudo graeca emerges from the nest in the natural habitat where it has incubated underground over the summer. Note the substrate which is a mix of fine soils and sand. There are also many small stones, particles of coarse gravel and remnants of dead vegetation. Tortoises like this will live their entire lives on such substrates. We routinely find very ancient animals! The suggestion that this is 'unsafe' is simply ridiculous.

Reference:

Gardner, S. C. and Oberdorster, E. (2005) Toxicology of Reptiles. CRC, Taylor & Francis.

328 p.

If you find these articles interesting and helpful, you can support our work by joining us and subscribing to the Tortoise Trust. We have been established since 1984 and we continue to provide original research and reliable information to tortoise and turtle enthusiasts worldwide. We also have two excellent online courses available, one for beginners and new keepers and one for advanced and professional keepers.

Copyright 2025 A. C. Highfield/Tortoise Trust