WHY CONIFERS WEEP

The true cause of a weeping growth habit is not completely understood. It appears to be related to an uneven distribution of growth auxins in the growing shoots of the plant. Gravity normally causes an auxin distribution that accelerates the growth of cells along the basal (bottom) side of a shoot and retards the growth along its dorsal (top) side, causing it to grow up and away from the ground. 

With a weeping plant, however, shoot growth is accelerated on the upper side and inhibited on the basal side.

This mutation may be encouraged in regions with heavy snowfall, where plants with weak lateral branches have the best chance of survival since they bend rather easily under heavy snow loads. In  regions without heavy snowfall a weak lateral branch would be shaded by stronger growing branches and die.

It is interesting to note a seasonal effect upon the tendency of conifers to weep. I had not noticed this until Al Fordham visited me when I lived in Pennsylvania. We observed that the newly elongated candles on a Pinus strobus 'Pendula' were all standing straight up, often to the extent that they curved up beyond the vertical. Even the previous year's growth, consisting of well hardened wood, had apparently been pulled up and extended horizontally.

Evidently, wood formed in spring on this cultivar exhibits "normal" growth. The new candles and/or shoots point straight up, and auxin activity causes the older wood to follow suit as it forms new wood. As the wood hardens and the branches thicken during the summer, the shoots turn down, producing a weeping conifer. I have noticed this effect on a number of pines. The pendulous spruces don't appear to do the same, perhaps because the new shoots are not as strong as those of a pine.

Auxins can rapidly bend old wood in the spring. I once laid a Picea glauca 'Conica' on its side when spring growth was at its maximum. In a few days the tree started to bend toward the sky. As the new growth hardened off, I stood the tree upright and the trunk was bent at a 90^o angle.

Hanging a pine upside down when the new growth begins causes a 180^o bend in the trunk in a little over a week, and repeated turning could produce a corkscrew effect in the trunk.

Counter Started July, 2003