Effectiveness of freezer storage in fulfilling the chilling requirement of fall-lifted ponderosa pine seedlings

The degree to which freezer storage fulfilled the chilling requirement of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) seedlings of two sources was determined by monitoring their development after potting or planting. The seedlings were lifted in September, October, November, or March and subjected to storage before outplanting. The fulfillment of chilling was assessed by measuring days to budbreak, cumulative percentage of seedlings flushing, foliated shoot length, and rate of bud abortion. The effect of freezer storage depended on stage of seedling development at lifting, length of storage, and seed source. Storage did not totally replace winter conditions, especially for seedlings lifted in September and October. Those from a high-elevation seed source flushed sooner than those from a low-elevation source. Delayed budbreak after planting of early lifted seedlings from the high-elevation source disappeared in the second year, but those from the low-elevation source continued to show effects. Seedlings lifted and stored in November had patterns of budbreak that were similar to those of seedlings that had overwintered in beds.