Ecodormancy is the third and last stage of dormancy. It is a ‘less dormant’ state in which a tree becomes more responsive to external environmental factors, but is prevented from growth because of response to those factors, such as the still present very cold temperatures. A tree in ecodormancy is slowly preparing for spring and becomes less and less cold-tolerant as spring (and bud burst) approaches.

The transition from endodormancy to ecodormancy is not apparent externally. Internally, callose continues to be broken down in the shoot meristems, unblocking plasmodesmata and restoring cell-to-cell communications within these. Bud growth ability is fully restored by the end of ecodormancy, but does not begin until the end of ecodormancy.

Expression of the DORMANCY-ASSOCIATED MADS-BOX (DAM) genes — growth suppressors — is less and less as ecodormancy progresses. Buds begin to accumulate starch reserves in readiness for new growth and development.

Callose plugs elsewhere throughout the tree now begin to degrade, which now opens up whole-tree communications. These callose deposits were laid down in the phloem during dormancy induction, and removal of these enables phloem sap to flow again. Phloem sap is a water-based fluid in which hormones, minerals and sugars are dissolved, and it is only when these growth-restoring components (including the water) can reach the buds will those be able to grow at all.

Production of the phytohormone (plant hormone) abscisic acid — which blocks phloem transport and cellular communications — declines and production of growth phytohormones such as auxins and gibberellin increases.

Xylem is the tissue that transports water from roots to the rest of a plant via capillary action. It is driven by transpiration, a passive process whereby water removed from leaves as a by-product of photosynthesis creates a water potential difference which draws water up from further down the plant. Xylem is non-functional throughout endodormancy, from both a lack of leaves driving that transpiration, as well as from air bubble blockages caused by repeated freeze-thaw cycles as winter progressed.

These blockages are removed during ecodormancy when the xylem is repaired. Starch in surrounding cells is broken down into sugars, which then move into the xylem cells. The increased sugar concentration creates an osmotic potential which drives (and eventually restores) water movement.

Expression of SHORT VEGETATIVE PHASE (SVP) genes increases during early spring — these are growth inhibitors which keep premature growth suppressed until bud break.

The tree is now ready for spring and a new growth and reproduction cycle.