The choice and condition of substrate is important because your tortoise spends all of his time on it when indoors. If it's too wet, he can develop shell rot, respiratory infections, and other health problems. If it's too dry, he can become dehydrated. Also, if you have asthma or allergies, it must be something that doesn't make you feel sick!
What works well for one tortoise keeper, may not work in another person's setup. You'll need to adjust your care and substrate choice based on your tortoise species, type of indoor setup, room humidity, and room temperature level. There is no one "best" substrate that works for every species in every situation.
You should exercise care to keep your tortoise's food substrate free regardless of what substrate you choose. No loose bedding is 100% safe to eat in large quantities, unless it's an actual food item like dried grass or edible leaf litter. Any non-food substrate may possibly cause intestinal obstructions if it is consumed in large enough quantities. Place food on a plate or tray when feeding, not directly on the substrate.
Plain garden soil, with no additives like fertilizers or perlite, is the most natural substrate for indoor tortoise pens. Soil can be used by itself or mixed with with other substrates like coconut coir or peat moss. Play with the mix to find the ratio you like best.
Pros of soil:
Cons of soil:
Sand and soil in outdoor tortoise pens is natural and perfectly fine, but using sand indoors is controversial. Many keepers have used sand for years in indoor substrate mixes with no problems, while others claim it should never be used because it can be accidentally swallowed with food.
Straight sand by itself is not recommended as an indoor substrate. The traditional indoor substrate formula is to mix plain soil with a small amount of play sand. This mix has worked well with burrowing Mediterranean species like Greeks.
Popular small particle indoor substrates for tortoises include coconut coir, soil & coconut coir mix, organic soil, and peat moss mixes.
Popular chip type substrates include fir / orchid bark, cypress mulch, and coconut husk chips. Also shown is sphagnum moss which is very soft when damp.
Allergywise, coconut husk substrates are the least irritating indoor substrates, at least for me. They are sold as small animal substrates, reptile substrates, soil amendments, and planting mediums. I look for coconut products that cleaned and prewashed before packaging.
The exact texture and composition of coconut husk products varies by the company, but below are generalized descriptions of the various types. Coir and chips are the most commonly available formats. Many sellers use the terms "coir" and" fiber" interchangeably for the finer ground husks, but typical coconut husk grades are:
1.) Coconut coir
Cconut coir substrate is available in loose or compressed form. When wet, this finely ground coconut substrate resembles coffee grounds. The expandable coconut coir is the cheapest. It comes as a compressed brick that will multiply in volume when soaked in warm water.
The quality of coconut husk products varies by the company. Some products are ground finer (coir) while others are coarser with longer fiber "hairs" (fiber). Some are almost odor free, while others smell more. Try different brands to see which one you like the best.
Coconut husk coir / fiber is sold under many different product names, including compressed coco coir, coco peat, organic growing medium, and wonder soil. Just check the package labels to confirm the contents are plain coconut fiber with no additives.
Pros of coconut coir:
Cons of coconut coir:
2.) Coconut chips
Coconut "bark" chips are the coarser version of coconut husk substrates. They are another popular indoor tortoise enclosure substrate choice because they are natural, nice looking, and easy to find. Coconut chips are the most allergy friendly substrate for me.
Pros of coco chips:
Cons of coco chips:
When I mention coco mulch, I am talking about cut and shredded coconut shells. I am not talking about cacao bean, aka cocoa (chocolate), shell mulch. Cacao bean shell mulch is toxic to dogs if the chemical theobromine has not been removed from it. Only use coconut shell husk chips and coir, not cacao bean mulch.
Sphagnum moss is a popular substrate for baby tortoises. If you do use moss, change it frequently because fungus growth and fungal spores in the moss can be a concern. Especially in cheaper, lower grade products.
I always buy the premium grade (AAA, 5 star), long fiber sphagnum moss from New Zealand for its quality and cleanliness. I use it in all my hatchling indoor enclosures and keep it slightly damp and warm. My babies love to burrow in it.
Pros of sphagnum moss:
Cons of sphagnum moss:
Expanding a 5 kg (11 lb) block of coconut coir. It took several buckets of water.
Expanding a 500 g (1.1 lb) block of compressed New Zealand sphagnum moss with water. It is very absorbent.
"Sphagnum moss" and "peat moss" are both from the Sphagnum plant, but they are not the same product. Note that one has the word "peat" in the name and the other one doesn't.
Sphagnum moss is the living moss growing on top of a sphagnum bog. It has long strands and is green or light tan in color. It looks like moss. Peat moss is the decaying and dead material at the bottom of the bog. Peat is medium or dark brown. It consists of small, fluffy particles and looks similar to coconut coir.
Peatlands are a rich source of biodiversity and help regulate the climate change. Once harvested, peat takes hundreds of years to regenerate. That's why peat is considered to be a non-renewable resource. Conservationists urge boycott of peat.
Pros of peat moss:
Cons of peat moss:
Wood chips and bark mulches are appealing looking natural substrates. Fir / orchid bark and cypress mulch are especially popular among American tortoise keepers.
Pros of wood chips:
Cons of wood chips:
Nowadays, many tortoise keepers have moved onto more humid indoor setups, even for dry area species. Higher ambient humidity is especially important for hatchlings and youngsters. Hot and dry enclosures expose tortoises to various degrees of chronic dehydration (losing large amounts of water) which can lead to kidney failure and, in worst cases, death. Warm, damp substrate areas and/or warm, humid hides help prevent fluid loss. Tropical species babies, like stars, can be kept in warm and humid vivariums (fully closed reptile enclosures, closed chambers).
Rabbit hay pellets and alfalfa pellets used to be popular indoor substrates for tortoises, but they are not recommended anymore because they are very drying, mold quickly, can cause infections, and may induce walking problems.
Similarly, paper has fallen out of favor as an indoor tortoise substrate because it's slick and not diggable. It's best suited for short term, temporary use. For example, in quarantine tubs, hospital tubs, or for brief, overnight stays indoors when no heating is required.
1.) Astma and allergy aggravation in keepers
Land tortoises are often recommended as some of the most suitable pets for asthmatics and allergics. Indeed, clean tortoises are odor and allergen free. But... the real problem is the substrate that tortoises live on when indoors.
Most wood chips, mulches, and soil mixes give out odors that can irritate sensitive people and cause astma and allergy exacerbations. Handling them with bare hands can also cause skin rashes in some individuals. Cypress and fir / orchid bark are probably the worst offenders allergywise. For me, both of those are totally intolerable.
Coconut coir and husk are less smelly and are better tolerated by allergics, but they can be quite dusty right out of the bag. When kept damp, some brands smell rather musty, too.
The only indoor substrates that I can personally tolerate without severe allergy flare-up are coconut chips and sphagnum moss. In my open-top tortoise tubs, dry or damp coco chips are fine, especially when the enclosures are not kept in my main living areas. In high humidity vivariums, the wet substrate I tolerate best is high quality sphagnum moss. Some brands of prewashed coconut chips are fine as well. All other indoor substrates make me unwell. I've tried.
2.) Impaction from substrate ingestion
Eating large quantities of any non-food substrate, on purpose or accidentally with food, can lead to a bowel obstruction. Severe intestinal blockages (impactions) can be fatal. Veterinarians have performed surgeries on severely impacted tortoises and other reptiles who have consumed excessive amounts of sand, coconut coir, wood chips, bark chips, and other substrates.
Thankfully, in well hydrated and not constipated tortoises, small amounts of substrate usually pass through without problems. A fiber rich diet will also help push any accidentally swallowed substrate along in the intestines.
With all loose substrates, it's best to provide a substrate free eating area to avoid accidental ingestion of bedding during feeding. You can serve food on a shallow tray, plate, dish, or tile. Also, double plating, i.e., placing a small feeding dish on top of a larger plate, helps keep substrate away from food. Do not place food directly on any loose substrate.
3.) Walking problems from unstable or slippery surfaces
Coarsely ground bark with large pieces can create an unstable, difficult to walk on surface in the enclosure for babies and young ones. Finely ground bark chips pack tighter making it easier for the tortoises to walk on it, but the smaller pieces are also easier to eat and swallow.
Smooth paper has a rather slippery surface. For subadult and adult tortoises, paper is ok for a short-term temporary use like in a hospital tank, but paper not recommended for small, developing youngsters. Any smooth and slippery surface can cause babies' back legs to slip out when they are moving about in the enclosure. This can lead to permanent gait problems, for example, splayed legs. A tortoise with splayed back legs cannot stand tall on straight legs. Rather, the legs are more or less spread out when the tortoise stands or walks.
Wet paper towels can be used for brand new hatchlings for a short while, especially if babies have residual yolk sacs. Paper towels are soft, give enough grip for walking, and can be kept damp for more humidity.