A small gap between raised-bed boards can let soil spill out and give weeds an easy start. Before closing it, check whether the boards are simply loose or whether the bed has shifted because of rot, roots, or pressure from wet soil.
Inspect the structure
Brush soil away from the joint and look for soft wood, loose fasteners, and a corner that has moved out of square. Do not lean heavily on a weakened board. If the timber is decayed, replacing the section will last longer than forcing it back together.
Reduce pressure
Remove only enough soil near the joint to let the boards move safely. Keep plants and roots protected. A bed packed tightly against a shifted board may spring back when disturbed, so wear gloves and keep hands clear of pinch points.
Reset and secure
Bring the boards into alignment and use exterior-rated fasteners appropriate for the material. Pre-drill near board ends to reduce splitting. Do not use treated scraps or unknown coatings where they may contact edible soil unless their use is approved for that purpose.
Restore the edge
Replace soil in thin layers and water lightly to settle it. Add a narrow mulch strip outside the bed to reduce splash and weeds, but keep mulch below the board’s top edge. Recheck the gap after heavy rain and at the end of the season.