Soils, Substrates, and Sustainability
overview
Are you potting up fully developed plants, or are you trying to propagate? What type of plants are you potting? Different plants thrive in different soils.
One way to categorize soils and substrates is into biodegradable, semi-biodegradable, and non-biodegradable. These categories can be further broken up into organic, inorganic, and dual-use
When it comes to each category, one isn’t more useful or more sustainable over the other. Usefulness depends on what you’re looking for:
1. aeration
2. drainage
3. water retention
4. physical structure
5. nutrient retention
6. nutrient supplementation
6. pH bufferingBelow are many different examples, with multiple uses and a wide variety of environmental impacts, pros, and cons. It’s up to each of us individually to decide what works best for us and our plants. Ultimately, the commercial sale of soil and substrates does carry global and local impacts. From harvesting, to production, to transport, each step leaves a footprint. Use of raw, renewable and reusable materials helps reduce this footprint.
More information on specific plant types and their preferred substrates is located on the Care Tips page.
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Charcoal
Pumice
Lava Rock (Scoria)
Clay Pebbles (LECA)
Chicken Grit
Biochar
Zeolite
Outdoor Rocks
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Fluval Stratum
Perlite
Vermiculite
Arqlite
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Worm Castings
Tree Fern Fiber (fine & coarse)
Sphagnum Moss
Coco Coir
Compost
Bark
Rice Hulls
Peat Moss
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inorganic substrates
lava rock, perlite, pumice, vermiculite, zeolite, chicken grit, LECA, ARQLITE, fluval, outdoor rocks
Natural and volcanic rocks last a long time (some basically forever) and reduce the amount of water required. However, many types are obtained by mining practices that result in habitat loss and chemical contamination of surrounding ecosystems.
It’s always best to source your supplies from close-by, ensure they don’t contain harmful additives, and check whether the company makes any attempt to mitigate their footprint.
There are many sustainable companies that are sourced and processed in the US, some of which are family-owned. Others, despite being outside the US, have strict quality control processes as well.
Some great examples of inorganic substrate suppliers are: Cali-Pon, Zeodorizer, Build-a-Soil, Arden Line, Sol Soils LECA, International Zeolite Corp.
LAVA ROCK – (red or black scoria) Formed when molten magma cools rapidly and solidifies on the ground during an eruption. Maximum drainage. Heavy. Provides structure to soil. Good for bottom layering. Doesn’t add extra nutrients. Holds nutrients added by other materials in the soil.
PERLITE – Lightweight volcanic silica glass. Doesn’t break down (degrade) but does break into smaller pieces/powder. Prevents soil compaction, good drainage, moderate water retention. Provides no nutrients. Non-renewable, requires high energy use for mining and production. Browns after long-term watering.
PUMICE – Type of lava rock containing gas bubbles in structure. Formed during violent eruptions when magma is ejected into the air, then rapidly cools. Lightweight. Holds water better than other lava rocks. Doesn’t add extra nutrients. Holds nutrients added by other additions. Requires less energy use for mining and production, even less than LECA.
VERMICULITE – Extracted by open-pit mining of a mineral compound that is then aggressively heated to induce expansion. Slightly acidic, does not pull moisture from plant when dry. Good for African violets, hydrangeas, ferns, berry bushes, begonias, and propagating. Breaks into smaller pieces and loses aeration benefits after a few years.
ZEOLITE – Microporous volcanic mineral. Nutrient retention, aeration, water management through absorption and slow release. Significant absorption of water. Filters out heavy metals. Can be mixed or used as a bottom layer.
CHICKEN GRIT – Avoid oyster shells, probiotics or other additives; can alter soil pH. Affordable alternative to pumice. Made of crushed granite, quartz, and flint. Improves drainage and aeration. Rinse clean before using.
CLAY PEBBLES (LECA) – Highly wicking, best for soils with constant moisture or at bottom of self-watering pots. Good for semi-hydroponics. Will pull moisture from plant if too dry. Rinse clean, then soak for 24 hours before using. Comes in various sizes.
ARQLITE (LECA ALTERNATIVE) - ‘Smartgravel’ made entirely of recycled plastic. Improves moisture retention and can be used as a top dressing. Reusable. Comes in two sizes. Does not pull moisture away from plant like clay pebbles do but also doesn’t wick the same either, meaning you need to keep water levels a little higher in semi-hydroponic setups.
FLUVAL STRATUM – Volcanic soil substrate from Japan. Contains Iron, potassium and magnesium, with a lower release of ammonia, which means it has a less dramatic effect on overall soil pH. Absorbs nutrients in added fertilizers to feed plant roots over time. Heavy but porous and clay-like. Used as a semi-hydroponic method (must be kept a little wet). Weighs down the pot and anchors the plant without limiting root growth. Encourages beneficial bacteria and nutrient uptake. Creates slightly acidic environment. Ideal for propagating, especially with hungry plants like Alocasias. Takes years to break down and lose nutrients.
OUTDOOR ROCKS - Outdoor rocks can be highly useful and mimic some of the properties of the above options. Larger rocks can be used in bottoms or tops of pots, and smaller rocks can be mixed into soil to aid in drainage and aeration. More porous rocks help with moisture retention. Avoid using large rocks mixed into the soil, as they can crush roots.
Summary
Out of these options, I really like pumice, zeolite, chicken grit, Fluval and outdoor rocks. Fluval is especially useful for propagation, and the other 4 are excellent for succulents, cactus and all tropical plants.
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Organic Substrates
charcoal, BIOCHAR, worm castings, compost, TREE FERN FIBER, SPHAGNUM MOSS, PEAT MOSS, COCO COIR, BARK
Below, we will explore the different types of organic substrates, what they’re used for and their impact. Like with inorganic rocks, some of these options require extensive mining, production and shipping procedures, while also providing very little benefit to your plants. Different sources online discuss conflicting opinions about impact and sustainability, which is why it’s always important to do your own research and make decisions that are right for you.
There are a lot of alternatives available—discussed here—many of which are easier on your wallet as well.
HORTICULTURAL/ACTIVATED CHARCOAL – Great drainage and aeration. Can be used as a bottom layer in pots. Filters toxins, contaminants and impurities. Have you ever taken your dog to the vet because they ate something bad? They likely administered activated charcoal to try to clean the “something bad” out. Excellent for orchids and succulents. Mass-production of charcoal does contribute to deforestation and pollution. You can make your own charcoal at home using yard waste. Avoid briquettes made for cooking, as these contain added chemicals that can kill or damage your plants.
BIOCHAR – Carbon-rich, porous. Improves soil structure and nutrient & water retention. Made from agricultural waste through pyrolysis. Risk with poor manufacturing; chemicals and heavy metals. Reputable brands perform routine laboratory quality control testing. Some use third-party labs, which provides another layer of control when ensuring environmental and agricultural standards. Biochar comes in multiple different sizes, ranging from a fine powder to large chunky pieces.
WORM CASTINGS – Worm poop. Looks like coffee grounds. You can ascertain purity of store-bought casting mixes by observing the texture. macro- and micro-nutrient-rich. Contains nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, zinc, copper. Introduces beneficial bacteria and fungi. Improves water retention and soil structure. Neutral pH. Should be used in addition to other fertilization methods. Can be made at home through process of Vericomposting—Highly sustainable; uses earth worms to break down kitchen waste. Store-bought versions are expensive and not as sustainable. Excellent for all plants.
COMPOST – Best done yourself at home by layering “green materials” (food, coffee grounds and plant scraps) with “brown materials” (dried leaves, cardboard, woody yard waste). Best done directly on the ground to allow for healthy microbes. Reuses food waste and yard waste at the same time. Excellent for all plants.
TREE FERN FIBER – Good water retention. Resistant to breakdown; can last several years. Coarse is better for extra aeration and drainage. Renewable, slow to decompose and sustainable if sourced from places that implement conservation efforts like New Zealand. Fine is better for more density. Both retain moisture well while also promoting air circulation around roots. Great for Orchids, African violets, and Begonias
SPHAGNUM MOSS – Antibacterial properties but can cause root rot with too much moisture. Used during WWI for wound dressings. Acidic; lowers pH in soil. Good for rooting and propagating. Excellent moisture and humidity retention and soil aeration. Good alternative to coco coir but also can be considered non sustainable due to carbon emissions during harvesting. (more info below under “Peat Moss”). Great in mixes needing more moisture retention, like for Orchids, Begonias, African Violets, Alocasias, and Anthuriums.
PEAT MOSS – Under layer of growing sphagnum moss. Harvested from bogs; sustainability varies from place to place. Certain areas, such as Colorado, have prohibited harvesting. Most of our peat and sphagnum comes from Canada, where there is less impact on the ecosystem due to availability and conservation efforts. Headed by the Canadian Sphagnum Peat Moss Association (CSPMA). Under 1% of Canada’s peat bogs are used for extraction. There are limits on how many years a bog can be harvested from. Peat holds up to 20x its weight in water. Good balance of nutrients. Add water before use. Wear gloves when handling, especially if you have any cuts or open wounds, due to risk of fungal infections. Good for all plants as an alternative to coco coir. An alternative to peat moss is PittMoss, made entirely out of paper waste.
COCO COIR – Generally produced through non-sustainable practices; high use of water, chemicals and energy for processing; contributes to pollution and greenhouse gasses; impacts local ecosystems to harvest; poses hazards to workers and communities if precautions not taken. Some areas, like Sri Lanka, have very strict production standards, waste management standards and worker protections. Fibrous, derived from coconut husks, which means it’s renewable. Neutral pH. Excellent water retention and aeration. Good for Alocasias and Anthuriums. Breaks down quickly. High in potassium but inhibits calcium absorption. Lasts longer than peat.
BARK – Wood chips, usually pine or fir. Provides structure, aeration, and drainage, with some moisture retention. In outdoor plants, can also protect from frost damage. Because of its moisture retention, it isn’t usually good for succulents and cacti, unless you live in a particularly dry climate like New Mexico. For succulents in NM, I find it helpful to have a little bit of bark in the soil because it protects them from drying out too much. I do not use bark in my cactus mixes at all though. Decomposes quickly, which means it needs to be replaced more frequently. Excellent for Orchids, Philodendrons, Hoyas, African Violets and Begonias.
summary
I use all of these, except for peat moss and coco coir (unless I’m reusing/recycling from other plants I’ve received from elsewhere)—Despite their ability to hold onto moisture, I find they don’t have enough benefits to outweigh the environmental cost, and they retain so much water, they tend to harbor pests. I’m especially fond of Biochar, worm castings, and tree fern fiber.
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dual-use substrates
rice hulls, mycorrhizae, leaf mold
These options are more like additives or fertilizers, however they have a dual purpose of providing soil-like properties like moisture retention, aeration, and root stabilization. More soil amendments will be discussed in the Fertilizer blog post.
RICE HULLS – Improves drainage; great alternative to perlite. Provides fertilization during breakdown; releases silica, which strengthens plants. Fungus gnat deterrent. Considered sustainable because they are renewable and a natural by-product of rice milling.
MYCORRHIZAE – Beneficial fungi powder. Has a dramatic positive effect on size and nutrient uptake of roots. Improves water retention, resilience and transplant success on a molecular level within the plant’s root system. Considered an eco-friendly alternative to synthetic fertilizers. Production is cost-effective and environmentally friendly, often done in a laboratory-like setting.
LEAF MOLD - Uses a long-term (1-2yr) fungal breakdown process that creates a nutrient-rich mulch. Can be produced yourself with a single ingredient —leaves—and minimal effort; every Fall, put leaves in a bag or bin—breaking them down beforehand either manually or with a shredder/mower helps—keep consistently moist and let sit. Excellent for outdoor gardening and seed starting. Improves moisture retention and temperature regulation during hot and cold months.
OYSTER SHELLS - Good slow-release source of calcium and lime, used as a pH buffering agent to correct overly-acidic soil. Provides structure to soil.
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Soil Mixes
Soil mixes are usually a combination of organic and inorganic substrates. As with individual substrates, mixes have many different uses and environmental impacts. The most widely-available commercial brands— like Miracle Gro—are not always the best choice, sometimes harboring unwanted pests, bacteria and fungi, while also providing little benefit to your plants.
PON MIX (VARIOUS BRANDS) - Pon mixes vary by brand, but ultimately, they’re a mix of volcanic rocks (zeolite, pumice, lava rock, etc.), clays (LECA, Akadama, ceramsite, etc.) and occasionally different types of bark. Everyone seems to settle on one or two brands that are their go-to; it all just depends on what you’re looking for: just drainage or also some water retention? Some of the most popular mixes are: Bonsai Jack, Lechuza-Pon, and Sol Soils. However, there are plenty of options online, so you’re guaranteed to find exactly what you’re looking for. It’s easy to order a couple different mixes and combine them into your own perfect recipe. Pon mixes can be used for succulents, cacti, propagation, and as an additive to other mixes to add more drainage.
AROID MIX (VARIOUS BRANDS) - As with other mixes, the ratios in your aroid mix of choice will depend on whether you want drainage, water retention, or both. Each brand varies pretty widely, but they usually contain a mixture of bark, volcanic rocks, sphagnum moss, worm castings, charcoal/Biochar, coco coir/fiber, LECA, and sometimes fertilizers/fungi powders. Instead of LECA, I prefer chicken grit and fern fiber. Aroid mixes are great for philodendrons, Alocasias and Anthuriums.
ORCHID MIX (VARIOUS BRANDS) - Depending on your orchid, you’ll want to go really chunky or chunky with a little moisture retention. If you don’t want to be watering and misting every single day, Orchids in NM generally need a little more moisture retention. Black Gold Orchid Mix with a little extra bark added, is actually ideal for most orchids in NM. My go-to is Gulber Orchids fine-grade bark with a little bit of sphagnum and fern fiber added.
BLACK GOLD CACTUS MIX - I honestly cannot say enough about Black Gold. Considered a sustainable choice, it’s organic, doesn’t have harsh chemical additives, and uses quality ingredients. The Cactus Mix is my favorite. You will see there is also a ‘Succulent & Cactus Mix’. My advice: stick with the straight Cactus because it is grittier, providing better drainage. You can use these mixes as an additive with other substrates, or you can use them as-is. I do it both ways, for a wide range of plants, not just succulents and cacti. Black Gold is available online, but I have also found it at Jackalope in Santa Fe & Albuquerque, and at Newman’s Nursery in Santa Fe.
ROSY SOIL - Despite being on the expensive side, great variety of different soil mixes while also being sustainable and eco friendly. Aroid, Orchid, Houseplant, Succulent & Cacti mixes are available.
FOXFARM(HAPPY FROG, OCEAN FOREST, BUSH DOCTOR) - These mixes are available in almost all the nurseries in NM. They’re known for having excellent nutrients like worm castings, bat guano, fish emulsion and crab meal. They do use peat moss, coco coir and perlite, but their peat is sustainably sourced from Canada.
Overall Summary
Through trial and error—and a little research—each grower finds which methods and materials work best for them and their plants. Whether you’re looking for moisture, air flow, nutrients or eco-friendliness, hopefully this post has given you some ideas of where to start.
