King Blue is the cold-loving cousin of the classic Blue Oyster. It forms firm clusters of deep slate-blue caps with thicker, meatier flesh and a longer shelf life, and it keeps fruiting in cool, unheated spaces through fall and winter.
- P. columbinusSpecies
- ~5 lbColonized grain
- 45–65°FFruiting temp
- BeginnerSkill level
- 12–13Master's Mix bags
Why grow King Blue from our spawn
Cold-weather fruiter
Fruits from 45 to 65°F, cooler than standard Blue Oyster.
Meatier texture
Thicker flesh and firmer clusters that keep longer.
Easy to grow
Fast, aggressive mycelium and beginner-friendly.
From bag to block
1Break it up
Squeeze and massage the sealed bag until the grain separates into loose kernels.
2Set up clean
For a simple Master's Mix spawn, a clean room with still air works. For grain-to-grain or other open work, use a flow hood.
3Spawn about 1:3
Roughly one part spawn to three parts substrate, or about 2 cups per 5 lb bag of sterilized Master’s Mix. One bag covers 12–13.
4Seal and wait
Seal the bags, mix thoroughly and let them colonize at 65–75°F before moving to fruiting conditions.
King Blue grain spawn specs
| Spec | Detail |
|---|
| Scientific name | Pleurotus columbinus |
| Mycelium | White, fast and strongly ropey |
| Grain | Mostly white and red millet with a little milo |
| Bag | Unicorn 3T, 3-mil, 0.22-micron filter patch |
| Sterilization | 3-hour autoclave cycle |
| Weight | 5 lb net; bags usually fill to about 5.5 lb |
| Spawn rate | About 1:3; one bag spawns 12–13 bags of 5 lb Master's Mix |
| Best substrates | Master's Mix, hardwood sawdust with bran, straw |
| Fruiting temperature | 45–65°F |
| Skill level | Beginner |
| Type | Gourmet |
| Shelf life | Best within about 90 days; up to 120 days refrigerated at 35–40°F |
| Ships | Same or next business day |
Where our genetics come from
Our master culture collection is the product of years of isolation work in our Illinois lab. We've added to it through a partnership with a leading commercial culture supplier in Canada and with select strains from the UK and Asia. Every culture is kept as first-generation commercial genetics and chosen for clean, vigorous colonization and fruit that's true to type.
Common questions
How is King Blue different from Blue Oyster?
King Blue fruits cooler, down to 45°F, and produces thicker, meatier caps with better texture and shelf life.
Where should I fruit King Blue?
Cool spaces work well: basements, garages and unheated rooms in fall and winter.
How long will the spawn keep?
Use it within about 90 days for the best results. Refrigerated at 35–40°F, it can last around 120 days.
Do I need a flow hood?
Not for a basic Master's Mix spawn in a clean, still room. For grain-to-grain expansion or other open work, use a flow hood or clean room.
What if the bag arrives damaged or contaminated?
Every bag ships fully colonized and is inspected first. If something's wrong, contact us within 5 days of delivery with a photo and we'll send a free replacement.
Made fresh, shipped fast
Each bag is sterilized for 3 hours in an autoclave, inoculated under HEPA-filtered laminar flow and left to colonize completely in a dedicated clean room, then inspected before it ships. Millet's small kernels mean more inoculation points per pound, so the spawn spreads quickly and evenly through your substrate.
We produce on a rolling schedule instead of stockpiling, so your spawn is fresh. It usually ships the same or next business day in padded packaging, with a free cold pack from May through September or for hot destinations.
King Blue spawn, fully colonized
Broken up and ready to spawn
When it arrives: Break up the grain and spawn it soon. If you can't use it right away, refrigerate it at 35–40°F.