Planting Primroses Outdoors: Frost Tolerance and Lunar Gardening Tips

When to Plant Primulas Outside

Primroses (Primula) are technically hardy, but their blooms are easily damaged by frost. In Rhode Island, keep them in a cool, bright, frost-free location indoors until the danger of hard frost has passed. The old rule of planting after the first full moon in May (the "Flower Moon") aligns roughly with the last frost date in many northern areas, but it's not a guarantee.

Lunar Gardening Perspective

Lunar gardening suggests the moon's gravity affects moisture in plants and soil. The Ed Hume Garden Almanac uses lunar phases to schedule sowing, transplanting, and fertilizing. Some gardeners, like R.J. Harris in England, report better results when following lunar cycles. However, the most critical factor for tender plants like impatiens and begonias is avoiding sudden frost—they are not cold-hardy and will be severely damaged or killed.

Recommendation

Keep primulas indoors until nights are consistently above freezing. Then harden them off gradually before planting in part shade. For impatiens and begonias, wait until all frost risk is gone.