Harvesting Your Vermicast

Section 7 of the Vermicomposting: Complete Guide

L.J.

Environmental Advocate

🌱 Vermicast: Nature’s Soil Booster

What Is Vermicast?

Vermicast—also called worm castings or worm poo—is the end product of a composting worm’s digestion. It’s a dark, crumbly, odourless material packed with nutrients, beneficial microbes, and organic matter

🪱 Vermicast Composition

Nutrients

🌱 Nutrients

Nitrogen (N) – for leafy growth
Phosphorus (P) – supports root development and flowering
Potassium (K) – boosts overall plant health and disease resistance
Micronutrients – calcium, magnesium, iron, zinc, and more in trace amounts

Microbial Life

🧫 Microbial Life

Beneficial bacteria and fungi – help break down organic matter and improve nutrient uptake
Enzymes – aid soil processes and plant resilience
Humic and fulvic acids – improve soil structure and nutrient availability

Organic Matter

🌿 Organic Matter

Partially decomposed plant material – adds texture and slow-release nutrients
Stable carbon compounds – improve moisture retention and aeration

🧪 What Vermicast Doesn’t Contain

No synthetic chemicals
No pathogens (if processed correctly)
Very low ammonia or salt levels compared to traditional manure

📆 When to Harvest

Once your wormery is thriving, you’ll start to notice signs that the vermicast is ready to harvest.

🌱 Signs of Finished Vermicast

Finished vermicast (worm castings) is the end product of healthy worm composting. It’s nutrient-rich, earthy, and ready to use when:

✅ Visual & Texture Clues

Dark brown or black colour
Fine, crumbly texture—like coffee grounds or soil
Few visible scraps—most food and bedding fully broken down
No shiny or slimy patches
Castings may feel slightly moist but not wet

👃 Smell Check

Earthy, fresh scent
No sour, rotten, or ammonia smells

🪱 Worm Behaviour

Worms may cluster in remaining bedding or migrate downward

🧪 Unfinished Vermicast: What to Do

Unfinished vermicast may contain worms, cocoons, bedding, or scraps that haven’t fully broken down.

The easiest option is to tip the unfinished vermicast directly back into the active bin—no sorting needed. Just scatter it across the surface or mix it lightly into the bedding. Worms will rework it, and any cocoons or scraps will continue breaking down naturally. Simple, quick, and zero waste.

Alternatively, you can use partially finished vermicast as mulch around plants or store and re-screen it once it has dried and further decomposed.

🌾 Vermicast Harvesting Methods

Once your worm bin is full of rich, crumbly castings, it’s time to harvest. There’s no single “right” way—just different methods to suit your setup, time, and comfort level. Whether you prefer hands-on sorting, gentle worm migration, or tidy tray systems, each approach helps you separate finished vermicast from worms and unprocessed material.

🚜 Common Harvesting Methods

Light Harvesting (using light to gently guide worms downward)
Dump & Sort (Manual Sorting)
Migration Method (Side/Upwards)
Screening (Sieve Separation)

💡 Tip: Harvest in Phases

Avoid stripping the entire bin at once. Leaving some vermicast behind helps maintain a healthy microbial balance and keeps your worm community thriving for continuous composting success.

💡 Light Harvesting Method

This method uses light exposure to gently encourage worms to burrow downward, making it easier to collect vermicast from the surface. Light Harvesting is ideal for small harvests.

How It Works

Worms naturally avoid light. When exposed, they burrow downward to escape it—leaving the upper layers of castings worm-free and ready to collect.

💡 Pro tip: Avoid direct sunlight on hot days—it can overheat and harm your worms.

📋 Step-by-Step Guide

Step 1: Remove the Top Tray

Lift out the tray with finished vermicast and place it on a flat surface

Step 2: Expose to Bright Light

Use natural sunlight or a lamp—worms will burrow downward to escape the light.

Step 3: Scrap Off Top Layer

Step 3: Scrape Off the Top Layer

Once the surface is worm-free, collect the castings in stages.

Step 4: Return Worms to Active Trays

Step 4: Return Worms to Active Tray

Any remaining worms or cocoons can be gently returned to the lower active tray.

💡It works best when the top tray is dryish and nearly finished, and avoids disturbing the lower layers.

🖐️Dump & Sort: Hands-On Vermicast Harvesting

Dump and sort involves emptying the entire bin, exposing the compost to light, and manually separating worms from finished castings in layers. It’s ideal for small bins, classroom demos, or anyone who enjoys a hands-on, observational approach.

📋 Step-by-Step Guide

Step 1: Prepare Your Harvesting Area

Lay out a tarp, tray, or large container lid in a well-lit space
Have a scoop, brush, and tub ready for collecting castings

Step 2: Dump the Bin Contents

Gently tip out the worm bin onto your surface
Break up compacted material into small mounds or cones

Step 3: Expose to Light

Use natural sunlight or a lamp to illuminate the mounds
Wait 5–10 minutes—worms will burrow deeper to avoid light

Step 4: Scrape Off Castings

Carefully remove the top layer of vermicast with a scoop or brush
Repeat every few minutes as worms continue to move downward

Step 5: Separate Worms & Unfinished Bits

Once mostly worms remain, transfer them to fresh bedding
Return any unprocessed scraps to the bin or pre-treat for next cycle

🪱 Migration Method

Migration methods work by creating a more attractive environment in a new area—whether it’s to the side, above, or below—you gently guide worms to relocate without force or disruption. This natural behaviour makes harvesting easier and keeps the bin ecosystem balanced.

Ideally, worm migration happens to the side or upward because these directions align with their natural instincts to seek fresh food and moisture.

➡️ Side Feeding: Worms move sideways toward fresh bedding and scraps added on one side, allowing you to harvest from the other.

⬆️ Upward Migration: Worms migrate upward into a fresh tray placed above the finished compost, leaving nutrient-rich castings below.

⬇️ While downward migration is possible by adding fresh material below, it’s less natural since worms usually avoid moving downward, making this method slower and less common.

How It Works

Worms instinctively move toward fresh food, moisture, and darkness, and away from light, dryness, and depleted zones

➡️ Migration: Side Feeding

Side feeding is a gentle, low-stress method that encourages worms to migrate naturally. By adding fresh bedding and food to one side of the bin, you create a clean zone for feeding while allowing the other side to mature into harvest-ready vermicast. It’s ideal for continuous composting, easy harvesting, and maintaining a balanced bin.

📋 Step-by-Step Guide

Step 1: Push Compost to One Side

Step 1: Push Compost to One Side.

Push the compost to one side of the bin
Gently move finished vermicompost to create space.
Avoid disturbing the worms too much.

Step 2: Feed Empty Side

Add fresh bedding and food to the empty side
Provide a fresh, inviting zone with moist bedding and new food scraps.

Step 3: Wait 1-2 Weeks for Worm Migration

Step 3: Wait 1–2 weeks for worms to migrate

Worms naturally move towards fresh food, leaving behind the castings.

Step 4: Collect Vermicast

Collect the vermicompost from the vacated side
Scoop out the nutrient-rich vermicast, free of most worms and scraps.

Step 5: Check for Leftover Worms and Cocoons

Step 5: Check for leftover worms and cocoons

Return any stragglers to the active bin area to keep your worm population healthy.

🔁 Rotate sides regularly to maintain a steady supply of vermicast without stressing your worms.

⬆️ Migration: Upwards Feeding

Upward migration uses worms’ natural tendency to move toward fresh food and moisture. By adding a new tray with fresh bedding and scraps above the finished compost, worms gradually migrate upward, leaving nutrient-rich vermicast behind in the lower tray. It’s a clean, low-disruption method ideal for multi-tray wormeries and staged harvesting.

📋 Step-by-Step Guide

Step 1: Wait Until Lower Tray is Nearly Finished

Step 1: Push Compost to One Side.

Push the compost to one side of the bin
Gently move finished vermicompost to create space.
Avoid disturbing the worms too much.

Step 2: Add New Tray on Top

Step 2: Feed Empty Side

Add fresh bedding and food to the empty side
Provide a fresh, inviting zone with moist bedding and new food scraps.

Step 3: Ensure Good Contact Between Trays

Worms need access—align holes or mesh so they can easily move upward.

Step 4: Leave for 1–2 Weeks

Worms will naturally migrate toward the fresh food and moisture in the upper tray.

Step 5: Check Migration Progress

Peek into the lower tray—fewer worms and cocoons means it’s nearly ready to harvest.

Step 6: Remove and Harvest the Lower Tray

Scoop out the vermicast, return any stragglers to the active tray, and store or use the compost.

Step 7: Repeat the Cycle

Rotate trays as needed to keep your wormery productive and low-maintenance.

⬇️ The method for downward migration is the same as upward migration, but with the trays arranged the other way around—fresh bedding and food go at the bottom, encouraging worms to move downward instead of upward.

🧺Screen Harvesting

Screen harvesting uses a fine mesh or sieve to separate finished vermicast from worms, cocoons, and bulky bedding.

🗂️ Multi-Tray Systems

Screening is useful for bottom trays
Once worms migrate upward, you can screen the lower tray’s contents.
Pairs well with staged harvesting
Rotate trays and screen castings every few weeks.

🧺 Single Tray Systems

Ideal for batch harvesting in standalone worm bins.
When castings are ready, screen the entire tray carefully to separate worms from finished compost.
Use light or food to encourage worms to migrate, then sift castings through a mesh sieve.
This method keeps your worm crew mostly undisturbed while allowing for periodic full harvesting.

How It Works

Screening separates fine vermicast from worms, cocoons, and chunky scraps using a mesh or sieve.

📋 Step-by-Step Guide

Step 1: Prepare a Screen or Sieve

Use a mesh with 2–5 mm holes—fine enough to separate castings from worms and larger bits.

🪴 Handy tip:
A fine-mesh garden sieve like this one is perfect for screening finished compost with ease.

Step 2: Scoop Out Bin Contents

Take a portion of the worm bin and place it onto the screen.

Step 3: Gently Shake or Rub

Let fine vermicast fall through while worms, cocoons, and unprocessed scraps stay on top.

Step 4: Sort & Return

Move worms and chunky bits back into the bin or a fresh bedding zone.

Step 5: Air-Dry the Vermicast

Step 5: Air-Dry the Vermicast (Optional)

If damp, spread thinly and let it dry slightly before storing or using.

💡 Tip: Screening works best when the bin is slightly dry—too much moisture clogs the mesh.

♻️ Resetting Your Worm Bin: By Bin Type

Single Tray Systems

When using a single tray wormery, you’ll usually refresh either one side of the tray at a time—gradually shifting worms to the fresh bedding side—or fully reset the whole tray if it’s empty. This staggered approach helps keep worms active while clearing out finished castings and old scraps.

Multi-Tray Systems

For multi-tray setups, the process is a bit more straightforward. Once the bottom tray is harvested and emptied, clean it thoroughly, refresh the bedding, and reset the tray completely before stacking it back. Meanwhile, worms continue processing scraps in the upper tray(s) without interruption.

🌿Where to Use Vermicast?

Worm castings are versatile and gentle, making them ideal for a wide range of garden and indoor uses. Whether you’re potting up houseplants, sowing seeds, or enriching garden beds, vermicast adds slow-release nutrients and boosts soil health naturally.

🪏 Add to Potting Mix

A balanced potting mix combines structure, drainage, and nutrition—worm castings add gentle nutrients and microbial life to support healthy plant growth.

⚠️ Avoid using 100% vermicast—it’s too dense for good drainage. Always blend with materials like coco coir, compost, or perlite for structure and airflow.

🌿 Garden Beds

Mix worm castings into the topsoil or apply around plants as a nutrient-rich amendment. Vermicast improves soil structure, boosts microbial life, and helps retain moisture—ideal for vegetables, herbs, and flowers.

🍅 Adjust quantities based on crop type—leafy greens and tomatoes love extra nutrition.

🪴 Houseplants

Sprinkle a thin layer of worm castings on the surface of indoor pots as a top dressing, or mix into the potting soil when repotting. Vermicast provides gentle, slow-release nutrients without risk of burning roots, supports microbial activity, and helps improve moisture retention—perfect for leafy greens, herbs, and flowering plants.

🌾 Mulch Layer

Apply unfinished or finished worm castings as a surface mulch around plants. They slowly release nutrients, support microbial life, and improve moisture retention. Unfinished castings continue breaking down, enriching the soil over time.

Layering works best: Use worm castings as the middle layer, topped with straw or leaf mould, and compost or coir beneath.
For containers: Blend castings with coco coir and compost for a tidy, nutrient-rich mulch.

🌱 Seed Starter Mix: A Gentle Boost for Young Roots

Seed starter mixes benefit from a small amount of worm castings to gently nourish seedlings and support healthy root growth.

A 2:1 ratio of coco coir to vermicast creates a light, well-draining seed mix with gentle nutrition—ideal for young seedlings and root development.

💡Pro tip: Keep worm castings to 25% or less of the mix to avoid nutrient overload for young seedlings.

☕ Worm Tea

Worm tea is a living liquid fertiliser made by steeping worm castings in water. It works by delivering beneficial microbes and soluble nutrients directly to your soil and plants.

How Worm Tea Works

🧪 Microbial Boost

Worm tea introduces active bacteria, fungi, and protozoa that help break down organic matter and release nutrients.
These microbes improve soil structure, aeration, and water retention.
They also help suppress harmful pathogens through microbial competition.

🌱 Nutrient Delivery

Castings release plant-available nutrients like nitrogen, phosphorus, and potassium into the water.
These nutrients are absorbed quickly by roots or leaves, especially when applied as a foliar spray.

🛡️ Plant Protection

Some microbes in worm tea can outcompete disease-causing organisms, reducing issues like root rot or mildew.
Foliar sprays may help plants resist pests and fungal infections.

🧬 Soil Health Over Time

Regular use builds a resilient soil ecosystem, supporting long-term fertility and plant vitality.
Especially useful in depleted soils, container gardens, or no-dig beds.

🫖 How to Prepare Worm Tea

For the cleanest and easiest brewing, start by bagging your vermicast. Using breathable bags (like muslin or mesh) keeps solids contained, makes aeration simple, and prevents your pump or sprayer from clogging. It also speeds up straining and ensures a smooth, rich liquid ready to feed your garden.

📋 Step-by-Step Guide

🫖 What You’ll Need:

Breathable mesh or muslin bag or cloth (possibly string if using cloth)
Finished worm castings (well-screened, no visible food scraps or worms/cocoons)
Dechlorinated water (let tap water sit for 24 hours or use rainwater)
Bucket or container (5–10 litres is typical)
Aeration (optional but recommended: aquarium pump and air stone)
Molasses or sugar (1–2 tsp to feed microbes—optional)

Step 1: Bag Castings

Step 1: Bag Vermicast

Scoop about 1 cup of vermicast into a breathable bag (muslin, mesh, old tights, etc.).
Gather the top edges of the bag.
Tie securely with string, elastic, or a knot—leave enough space for water to flow through.
Make sure the bag isn’t too tightly packed to allow proper steeping.

Step 2: Place Bag in Water

Step 2: Place the bag in water

Always use a clean bucket or container to avoid introducing unwanted contaminants.
Use about 5 litres of water per verrmicast bag.
Use dechlorinated water- either rainwater or let tap water sit for 24 hours.
Place the vermicast bag- ensure it is fully submerged.

Step 3: Add Molasses (optional)

Step 3: Add molasses (optional)

Stir gently to dissolve.
This boosts microbial activity.

Step 4: Aerate

Step 4: Aerate for 12–24 hours

Use a pump and air stone to bubble air through the mix.
If skipping aeration, stir occasionally and steep for 12–24 hours.

Step 5: Remove Bag

Step 5: Remove the bag

Compost the spent vermicast (or add to plants)
Strain the liquid if using a sprayer.

Step 6: Use Immediately

Apply within 4–6 hours for best microbial benefit.
Pour around plant roots or mist leaves (strain well for foliar spray).

Step 7: Clean the Bag

Rinse thoroughly after use
If needed, soak in warm water with a little splash of white vinegar.
Let it dry completely (airdrying is best)
Reuse for the next batch.

How to Use Worm Tea:

🚿 Worm Tea Soil Drench

Pour gently around the base of each plant
Apply every 1–2 weeks during active growth
Avoid waterlogging—just enough to moisten the root zone

✅ Why It Works:

Delivers nutrients and microbes straight to the roots
Improves soil structure and microbial activity
Helps plants recover from stress or boost growth

🌿Worm Tea Foliar Spray

Strain the tea well to avoid clogging your sprayer
Spray in the early morning or evening to prevent leaf burn
Coat both the top and underside of leaves

✅ Why It Works:

Delivers nutrients quickly via leaf pores
Helps plants resist pests and fungal diseases
Boosts microbial life on leaf surfaces

🧪 Worm Tea as a Compost Booster

Pour worm tea evenly over your compost pile or bin
Apply after turning or adding new layers
Use every 1–2 weeks during active composting
Works well with Bokashi, hot composting, or traditional heaps

✅ Why It Works:

Adds active microbes that help decompose food scraps, garden waste, and bedding faster
Reintroduces beneficial bacteria and fungi, especially after turning or adding dry material
Helps balance carbon-to-nitrogen ratios by energising microbial life

🪱 How to Store Vermicast (Worm Castings)

Proper storage keeps your castings alive and effective, preserving their microbial richness for worm tea or soil use.

Use breathable containers
- Paper bags, cardboard boxes, hessian sacks, or plastic tubs with air holes
- Avoid airtight containers—microbes need oxygen
Keep it cool and dark

- Store in a shed, cupboard, or shaded area
- Avoid direct sunlight or heat, which dries out and damages microbes
Maintain moisture

- Castings should feel like a wrung-out sponge
- Mist lightly if they start to dry—never soak
Stir occasionally

- Gently fluff or turn every few weeks to prevent compaction and anaerobic pockets
Use within 6 months

- Fresh is best, especially for worm tea
- Older castings may lose microbial activity but still offer soil structure and slow-release nutrients

Looking to customise your setup or explore handy add-ons that make worm composting even easier?

From moisture meters and insulation wraps to feeding funnels and sieves, there are plenty of extras that can enhance your system. For ideas, recommendations, and practical tips, head over to Section 8: Optional Extras.