Terrarium Soil:

Best Type of Soil Mix for Enclosed Terrariums

The best soil mix for an enclosed terrarium is one that is well-draining, nutrient-rich, and slightly acidic to neutral in pH. This type of mix mimics the natural soil conditions of many terrarium-friendly plants and allows for good root health, adequate moisture retention, and optimal nutrient uptake.

Why Other Soils Are Not Ideal:

1. Garden Soil: Garden soil is too dense and doesn't provide good aeration, leading to waterlogging and root rot.
2. Potting Soil with Added Fertilizers: Over-fertilization can be an issue in a closed terrarium environment as it can lead to nutrient imbalances.
3. Sand: While it drains well, it doesn't hold nutrients or moisture well, making it unsuitable as the primary soil component.
4. Peat Moss: While useful in mixes, it can be too acidic when used alone and tends to become waterlogged.
5. Vermiculite: Retains too much water, leading to poor drainage and increased risk of root rot.

Good Ingredients for Terrarium Soil Mix:

1. Coconut Coir: Provides good water retention and aeration.
2. Orchid Bark: Improves drainage and adds texture.
3. Charcoal: Acts as a natural filter, reducing odors and improving soil quality.
4. Perlite: Improves aeration and drainage.
5. Sphagnum Moss: Good for moisture retention, also has antibacterial properties.
6. Worm Castings: Adds nutrients without the risk of over-fertilization.
7. Pumice: Enhances drainage and aeration.
8. Pine Bark Fines: Good for aeration and retains slight moisture, making it suitable for a variety of plants.

Ingredients Commonly Used but Not Ideal:

1. Gravel: Often used as a base layer for drainage but can make the soil mix too heavy, leading to poor aeration.
2. Calcined Clay: Can alter the pH of the soil, making it less suitable for some plants.
3. Wood Ash: Changes the pH and can be too alkaline for most terrarium plants.
4. Wood Matter: In most cases adding wood matter significnatly increases the chances of mold growth. It can work if certain precautionary steps are taken as outlined below. 

Adding Wood Matter: Organic wood matter if untreated will mold quickly in terrarium conditions. The enclosed, humid nature of terrariums creates an ideal environment for mold and fungi to grow, and this risk is heightened when wood is included without proper preparation or care.

Wood elements like bark, chips, or decorative pieces should be carefully selected and properly treated to minimize the risk of mold. Here are some precautions you can take:

1. Sterilize: Boil or bake the wood to kill any existing mold spores or bacteria.
2. Dry: Make sure the wood is completely dry before adding it to your terrarium to discourage mold growth.
3. Seal: Consider sealing the wood with a non-toxic sealant to create a barrier against moisture.
4. Monitor: Keep an eye on humidity levels and make sure they don't get too high; excess moisture is a leading cause of mold growth.
5. Ventilation: Even in an enclosed terrarium, especially new terrariums, occasional opening of the lid to allow airflow can help prevent mold.

If you do notice mold, remove the affected wood immediately to prevent the mold from spreading to the plants and soil in the terrarium. Replace it with a sterilized piece or consider using a different type of material that's less prone to mold growth.

So while wood can add a natural and visually appealing element to a terrarium, it does require more caution and care to use safely.

In an enclosed terrarium, the soil ecosystem has to be self-sustaining to some degree, so choosing the right soil mix is crucial. Combining these ingredients in varying proportions, depending on the specific needs of your plants, will give you the best chance of creating a thriving, long-lasting terrarium.