Midwest's Select Bulk Substrate Casing Mix - 5 pounds
Midwest's Select Bulk Substrate Casing Mix - 5 pounds is backordered and will ship as soon as it is back in stock.
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Description
Description
Midwest's Select Bulk Substrate is a pasteurized, pre-hydrated CVG mushroom substrate — coco coir, vermiculite and gypsum with lime and trace minerals — ready to mix with colonized grain spawn straight out of the 5 lb bag.
It's our top-selling bulk substrate, built for monotubs, trays and bins. Every bag arrives at field capacity with a balanced pH, so there's no soaking, measuring or pasteurizing on your end — just spawn to bulk and grow.
- 5 lbsPer bag
- CVGCoir, vermiculite, gypsum
- PasteurizedReady to use
- 2:1–3:1Substrate to grain
- 6 monthsRefrigerated, sealed
Why growers pick Select Bulk Substrate
- Ready to use – Pre-hydrated to field capacity and pasteurized. No soaking, mixing or measuring — open the bag and add colonized grain spawn.
- Pasteurized, not sterilized – Pasteurization knocks back competing microbes while keeping the substrate's natural biology, which is what you want in a bulk grow.
- Balanced pH and minerals – Hydrated lime and gypsum buffer the pH, and Azomite trace minerals round out the blend for vigorous mycelial growth.
- Consistent batch to batch – Same texture, moisture and pH in every bag, so your results are repeatable from one tub to the next.
- Trusted since 2011 – More than 100,000 bags sold to over 50,000 growers.
How to use it
- Start with fully colonized spawn. Grain spawn bags or jars should be completely white before you spawn to bulk.
- Break up the spawn. Massage the bag or shake the jar until the grain separates into loose kernels.
- Open the substrate. Crumble any clumps so the substrate is loose and even.
- Mix it in the tub. Combine spawn and substrate evenly in a clean monotub or tray, then level and lightly press the surface.
- Colonize, then fruit. Cover and leave it undisturbed until the surface is colonized, then introduce fruiting conditions.
Breaking up colonized spawn and mixing it into bulk substrate.
Bulk Growing Guide included. Our step-by-step bulk monotub guide walks you from colonized grain spawn to a fruiting tub.
How much do I need?
One 5 lb bag handles a small tub on its own. For bigger tubs, match your substrate to your spawn:
| Monotub | Substrate | Grain spawn |
|---|---|---|
| Small 28Q | About 4 lbs | 1 spawn bag or one 32 oz jar |
| Medium 44Q | 7.5 lbs (1½ bags) | 1 spawn bag |
| Large 66Q | 10 lbs (2 bags) | 2 spawn bags |
Specifications
| Specification | Detail |
|---|---|
| Weight | 5 lbs per bag |
| Base | Coco coir, vermiculite and gypsum (CVG) |
| Additives | Hydrated lime, mineral water, Azomite trace minerals |
| Treatment | Pasteurized |
| Moisture | Pre-hydrated to field capacity — no water needed |
| Spawn ratio | 2:1 to 3:1 substrate to grain |
| Works with | Rye, millet, 5-grain and other colonized grain spawn |
| Storage | Sealed, cool and dry; refrigerate up to 6 months; do not freeze |
Storage: Keep bags sealed in a cool, dry place for short-term storage, or refrigerate sealed bags for up to 6 months. Do not freeze, and avoid heat, direct sun and big temperature swings that cause condensation inside the bag.
Growing more than one tub?The 30 lb Select Bulk Substrate 6-Pack gets you six bags at a lower per-bag price, and our 7.5 lb bag fills a Medium 44Q tub in one go. Pair it with our Premium 5-Grain or Original Rye spawn bags.
FAQ
What is in Select Bulk Substrate?
A CVG base — coco coir, vermiculite and gypsum — with hydrated lime to buffer pH, mineral water and Azomite trace minerals. It comes pre-hydrated and pasteurized.
Do I need to add water?
No. Every bag is hydrated to field capacity before it ships. Open it, break up any clumps and mix in your colonized grain spawn.
Is it pasteurized or sterilized?
Pasteurized. That reduces competing microbes while keeping the substrate's natural biology, which is the standard approach for bulk substrate. Your grain spawn is what gets sterilized.
How much do I need for my monotub?
About 4 lbs for a Small 28Q, 7.5 lbs (1½ bags) for a Medium 44Q and 10 lbs (2 bags) for a Large 66Q.
What grain spawn can I use?
Any fully colonized grain spawn — rye, millet, 5-grain bags or grain jars. Aim for 2:1 to 3:1 substrate to grain.
Can I use it as a casing layer?
Yes. Mix it through as your bulk substrate, or spread a thin layer over colonized substrate as a casing.
How should I store it?
Keep bags sealed in a cool, dry place short-term, or refrigerate sealed bags for up to 6 months. Do not freeze.
