Pine Cones on Arborvitae

[Fotheringay-Phipps]

I've had a bunch of Nigra Arborvitae for the past few years, and they grow cones (which begin as light green buds and eventually turn brown). The thing is that the amount of cones on a given bush varies tremendously, where some of them are covered with them and look spotted even from a distance, to others that have only a few here and there, if any. And it changes from year to year - some of the ones that have the most cones one year have relatively few the next, and vice versa.

I understand that the purpose of cones is for reproduction etc. My question is what determines whether a given plant puts out a lot or a few of them?

[AskNott]

Maybe you knew this part, but the female bears cones.

Like many trees and shrubs, your arborvitaes are probably affected by the weather at the time of flowering. An early warm spell will trick blooms into getting frozen. A late cold snap will also kill blossoms. A year of ideal rain, bees, and sun will produce a big crop of cones. You never know.

[Fotheringay-Phipps]

Originally Posted by AskNott

Maybe you knew this part, but the female bears cones.

Actually I am under the impression that there are male and female cones, on the same plant.

Like many trees and shrubs, your arborvitaes are probably affected by the weather at the time of flowering. An early warm spell will trick blooms into getting frozen. A late cold snap will also kill blossoms. A year of ideal rain, bees, and sun will produce a big crop of cones. You never know.

Thanks.

My question is about variations between different shrubs. IOW why, in the same year, does Shrub A have much more cones than Shrub B? And why, if in 2008 Shrub A had a lot more cones than Shrub B, does this reverse in 2009, with Shrub B now having much more cones than Shrub A?

(I'm particularly interested to know whether these indicate anything about the relative health of the two shrubs.)

[Plynck]

Arborvitae are monoecious, so they have both male and female reproductive units on the same plant. As opposed to (say) hollies, which will only produce berries on the female plant and require a male close by for fertilization.

As with any evergreen, arborvitae can be affected by lime spread on nearby lawns. A lot of people like to surround their turf grass areas with a hedge of arborvitae, and don't realize that lime applications too close to the trees can actually affect their health. If you've ever seen them turn that sickly yellowy-green color, you'll know what I mean. I don't know where your garden is, or what grows there, but this might be causing your problem.

ETA: Looks like you already picked up on the monoecious thing, although the male parts can't really be called cones. And just to be a nitpicker: Your title refers to "pine cones" on an arborvitae, which would be quite noteworthy

Also, I know that some flowering trees alternate between years of outstanding flowers, and years of just normal flowering. It could be that you have two with alternating years?