Craft Your Own Black Gold

Craft Your Own Black Gold: DIY Potting Soil for Thriving Plant Boxes (Featuring Coco Coir, Vermiculite, Perlite & Worm Castings)

Tired of endlessly buying bags of potting mix? Want more control over what your precious plants are growing in? Creating your own custom potting soil for your plant boxes all a is easier than you think! Not only can it be more economical in the long run, but it also allows you to tailor the mix to your plants’ specific needs.

This guide will walk you through creating a fantastic, well-draining, and nutrient-rich potting mix using four superstar ingredients: coco coir, vermiculite, perlite, and worm castings. We’ll also delve into an important consideration with coco coir: the difference between washed and unwashed, and how to prepare it.

Why Make Your Own Potting Soil?

• Cost-Effective: Especially if you have many plant boxes, mixing your own can save you money.
• Quality Control: You know exactly what’s going into your mix – no mystery ingredients.
• Customisation: You can adjust the ratios to suit different plant types (e.g., more drainage for succulents, more water retention for leafy greens).
• Sustainable: Using ingredients like coco coir can be more environmentally friendly than peat moss-based mixes.
• It’s Rewarding! There’s a certain satisfaction in creating the perfect growing medium for your plants.

 

Understanding Your Ingredients: The Building Blocks of a Great Mix

1. Coco Coir:
   • What it is: A natural fiber extracted from coconut husks, coco coir is a popular and sustainable alternative to peat moss.
   • Benefits: Excellent water retention while also providing good aeration. It re-wets easily (unlike peat moss, which can become hydrophobic when dry) and has a neutral pH. It’s also slow to break down, meaning your mix will last longer.
   • Forms: Often sold in compressed bricks or blocks, which need to be rehydrated, or as loose coir.
2. Vermiculite:
   • What it is: A naturally occurring mineral (magnesium-aluminium-iron silicate) that is heated to expand it into lightweight, absorbent particles.
   • Benefits: Excellent at retaining water and nutrients, releasing them slowly to the plants. It also improves soil aeration and cation exchange capacity (the soil’s ability to hold onto essential nutrients). Its accordion-like particles hold moisture without becoming waterlogged.
3. Perlite:
   • What it is: A volcanic glass that is heated until it puffs up, creating very lightweight, porous, white granules.
   • Benefits: Primarily used to improve aeration and drainage. It creates air pockets in the soil, preventing compaction and ensuring roots get enough oxygen. It doesn’t hold water itself, but helps water drain through the mix more effectively.
4. Worm Castings (Vermicompost):
   • What it is: Essentially, worm poop! It’s a nutrient-rich organic amendment created as earthworms digest organic matter.
   • Benefits: A powerhouse of readily available nutrients and beneficial microbes. Worm castings improve soil structure, aeration, and water retention. They can also help protect plants from certain pests and diseases. Think of it as a natural, slow-release fertiliser and soil conditioner.

Coco Coir: Washed vs. Unwashed – What You Need to Know

Coco coir is processed in various ways, and one crucial distinction is whether it’s “washed” or “unwashed.”

• Unwashed Coco Coir: Coco palms are often grown near coastal areas, meaning the husks can absorb sea salt (sodium chloride). If this salt isn’t washed out during processing, it can remain in the final coco coir product. High salt levels can be detrimental to many plants, potentially burning roots, hindering nutrient uptake, and stunting growth. Unwashed coir might also have a higher level of potassium and chloride, which can be problematic for some plants.
• Washed Coco Coir (or Buffered Coco Coir): This coir has been rinsed, usually with fresh water, to remove excess salts. Sometimes, it undergoes an additional “buffering” process, where it’s treated with a calcium nitrate solution. This helps to displace sodium and balance the cation exchange sites, making nutrients like calcium and magnesium more readily available to plants.

Why is this important? Using unwashed coco coir with high salt content can lead to plant health issues. While some rugged plants might tolerate it, many, especially seedlings and salt-sensitive species, will suffer.

How to Tell the Difference:

Reputable suppliers will usually state whether their coco coir is washed or buffered. If it’s not mentioned, or if you’re buying a very cheap, unbranded product, it’s safer to assume it might be unwashed or have higher salt levels. Some coco coir packaging will provide an EC (Electrical Conductivity) level – a lower EC generally indicates lower salt content.

Steps to Wash Unwashed Coco Coir:

If you suspect your coco coir is unwashed or want to be extra cautious, here’s how to wash it:

1. Rehydrate (if using a brick): Place your compressed coco coir brick in a large container (a large bucket, tub, or wheelbarrow). Add the amount of warm water specified on the packaging (or enough to fully saturate and expand it). Let it sit for several hours or overnight until it’s fully expanded and crumbly.
2. Prepare for Rinsing: Once expanded, the goal is to flush out the excess salts. You can do this in a few ways:
   • In the Container: If your container has drainage holes, you can repeatedly flood the coir with fresh water and let it drain.
   • Using a Fabric Bag/Pillowcase: Place the rehydrated coir into a large mesh bag, old pillowcase, or cheesecloth-lined colander. This makes it easier to handle.
3. Rinse Thoroughly:
   • Pour fresh water over the coco coir.
   • Let the water drain through completely. You might see brownish water initially; this is normal as it also washes out some tannins.
   • Repeat this flushing process 3-5 times, or until the runoff water becomes clearer. Some people use an EC meter to test the runoff and continue washing until the EC drops to a safe level (generally below 0.5 mS/cm for sensitive plants, though this can vary).
4. Squeeze Out Excess Water: After the final rinse, gently squeeze out as much excess water as possible. The coir should be damp but not sopping wet.

Now your coco coir is ready to be used in your potting mix!

DIY Potting Soil Recipe for Plant Boxes

This is a good general-purpose recipe. Remember, “parts” can be any unit of measure (a scoop, a bucket, a yogurt container) as long as you use the same unit for all ingredients.

• 2 parts Coco Coir (pre-washed and rehydrated if necessary)
• 1 part Perlite
• 1 part Vermiculite
• 1 part Worm Castings

Why this ratio?

• Coco Coir: Forms the base, providing good water retention and structure.
• Perlite: Ensures excellent drainage and aeration, preventing the mix from becoming too compact or waterlogged – crucial for container gardening.
• Vermiculite: Boosts water and nutrient retention, acting like a sponge to hold moisture and release it as needed.
• Worm Castings: Provide a natural, slow-release source of essential nutrients and beneficial microbes to get your plants off to a great start.

How to Mix Your DIY Potting Soil:

1. Gather Your Materials: You’ll need your ingredients, a large mixing container (like a tarp, wheelbarrow, or large tub), and a trowel or shovel for mixing. Wearing gloves and a dust mask is also a good idea, especially when working with dry ingredients like perlite and vermiculite.
2. Moisten (if needed): If your coco coir is very dry (even after rehydration), lightly moisten it. This helps reduce dust and makes mixing easier. Don’t make it soggy.
3. Add Ingredients: Add the coco coir, perlite, vermiculite, and worm castings to your mixing container according to the ratios above.
4. Mix Thoroughly: Combine all the ingredients well. Break up any clumps of coco coir or worm castings. The goal is a uniform, loose, and crumbly mixture. Ensure the perlite and vermiculite are evenly distributed throughout the coir and castings.
5. Check Consistency: The final mix should feel light and airy. When you squeeze a handful, it should hold its shape loosely but crumble easily when poked. It shouldn’t be overly dense or muddy.

Using and Storing Your DIY Potting Soil

• Using: Your freshly made potting soil is ready to use in your plant boxes! Fill your containers, leaving adequate space for your plants and watering.
• Storing: If you make a large batch, you can store the excess in a sealed container (like a bucket with a lid or a heavy-duty plastic bag) to keep it clean and prevent it from drying out completely or becoming contaminated. Store it in a cool, dry place. If it does dry out significantly, you may need to re-moisten it slightly before use.

A Note on Adjustments

This recipe is a great starting point. As you become more experienced, you can adjust the ratios based on your specific plants and conditions:

• For plants that prefer drier conditions (e.g., succulents, Mediterranean herbs): Increase the proportion of perlite for faster drainage. You might reduce the vermiculite.
• For moisture-loving plants (e.g., ferns, many leafy greens): You could slightly increase the coco coir or vermiculite content.
• For heavy feeders: You might incorporate a bit more worm castings or add a slow-release organic fertilizer to the mix.

By understanding your ingredients and being willing to experiment a little, you can create the perfect homemade potting soil to help your plant box gardens flourish like never before!