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USING NITROGEN-FREE FERTILIZER FOR PINES




Nitrogen free fertilizers, such as 0-10-10 divert a tree's energy from vegetative growth (new shoots and foliage) into strengthening roots, setting flower buds, and increasing girth by expanding and hardening young cells. For this reason they are commonly used in bonsai and in general horticulture as a late season feed for most deciduous broadleaved, flowering and fruiting species. However, few people realize that you can reverse the timing of nitrogen-free fertilizer for most pines to great effect, particularly pines with unacceptably long needles.

Most pines are programed for one flush of growth per year: the candles grow, needles lengthen and harden off, and that's the end of the season's growth until next spring. (Virginia pine and pitch pine are notable exceptions to this trend - they regularly produce successive flushes of growth during the season - but the feeding regimen outlined here can still be used to great effect. However, it would be counter-productive on Japanese black pine, where early season vigor is critical to inducing the shorter-needled second flush.)

Pinching young extending candles early in their development is one way to reduce needle length, as is withholding water, keeping the soil barley moist.  Cutting candles hard back, or even removing them completely is the normal way to induce adventitious buds. But you can't always do both, and if you try, the double shock may be too much for many western pines to tolerate, especially on an annual basis.

Not to worry, both of these desirable responses (short needles and adventitious bud production) can be induced and enhanced by feeding regularly with a nitrogen-free fertilizer throughout spring and early summer, while the pines are in active growth and candles and needles are still expanding.


The lack of nitrogen will keep needles short and dense. Candles will extend much less than normal, keeping internodes short and compact. (Many small shoots from last year's adventitious buds will not even need to be pinched.) The buds that naturally form at the candle tips or where candles have been cut or pinched will be smaller than normal, in turn producing smaller candles and needles when they open next year.

In late summer and fall, there's no need to divert energy away from vegetative growth with pines, simply because there's not going to be any no matter how heavy you feed regular balanced fertilizer.  But - if given liberal doses of all-round fertilizer in the second half of summer through fall, pines will begin to initiate new growth buds wherever they can, and this process will continue well into winter as the nitrogenous nourishment as still active in the tree. Buds will be more prolific in all the places where you would expect to see them - the base of pinched candles, last year's internodes, etc. - plus they will begin to pop out on older wood in places where you would not normally expect.

This all makes sense, since late summer through fall and into winter is when pines normally produce and set buds for next year. But the adventitious buds you have induced by 'reverse fertilizing' won't be fat extension buds that burst into thick vigorous candles in spring.  They are newly-formed emergency buds that have been produced from scratch, so they will be relatively small, in balance with the smaller buds that the nitrogen-free spring and summer feeding helped to induce at the ends of the current year's candles.

Thus our 'reversed fertilizing' regimen not only encourages small needles, short internodes, adventitious buds and dense, compact foliage this year, but also next.