Guide / Storage
Keeping pallets sound through storm season
Keep pallets off bare ground, under cover and in moving air through Oklahoma's storm season, which runs mainly March through June. Wood below 20% moisture content will not support mould, and a May rain can lift an uncovered stack well past that.
What the season does to a stack
Tornado season in Oklahoma City runs mainly March through June and peaks in April and May. About 150 tornadoes have struck within city limits since 1890. The same months are the wet ones: May averages about 5.3 inches of rain at the airport station, and Norman's wettest month is May at about 4.7 inches. Oklahoma City sees 36.4 inches a year over 83 days, Norman 37.7 inches over 85 days (NOAA 1991-2020 normals).
None of that is a reason to fear for the stack. It is a reason to move it before the season starts. Pallets stored flat on soil wick moisture up; stacks under a tarp that is closed on all sides trap it.
Average rain by month
| Month | Rain | What it means for a stack |
|---|---|---|
| January to February | 1.3 to 1.4 | Dry; cold slows mould. Good time to sort and restack. |
| March | 2.6 | Season starts. Get stacks off the ground now. |
| April | 3.6 | Wet and stormy. Cover, with airflow. |
| May | 5.3 | Wettest month. Uncovered stacks climb past 20% moisture content. |
| June | 4.5 | Warm and wet: the worst mould weather. |
| July to October | 3.3 to 3.7 | Hot; wet pallets dry fast if they can breathe. |
| November to December | 1.7 to 1.8 | Dry again. Move what is left. |
Four moves that matter
- Get it off the ground. Put a base layer of sacrificial pallets or timbers under the stack so air passes beneath.
- Cover the top, not the sides. A roof sheds rain; wrapped sides hold moisture in. Even a few feet of air velocity helps prevent mould.
- Keep the stack short and square. Tall stacks lean in wind; a stack of two to four layers is safe to handle.
- Rotate. Use or move the oldest stack first. The pile that sat longest turned grey first.
Heat-treated pallets are not immune. Loaded into a van while still hot they grow mould. See the moisture guide for how to read what you have.
When to stop storing and sell or clear
If a pile has been outdoors through a full wet season, the best move is often to stop treating it as stock. Grey boards, soft corners and a musty smell mean the wood is heading toward grinding. Send a photo and a count as a mixed load or arrange a pickup before the next season.
Questions, answered
How do you keep pallets from molding outside?
Get them off the ground, cover the top but not the sides, keep air moving and keep the stack short. Wood below 20% moisture content will not support mould.