The Myth of 0-10-10

[This post first appeared on Bonsaisite on 8/9/06]

It always amazes me that folks latch on to no nitrogen fertilizer when preparing for winter, when it is the least important of several factors pertinent to hardening off.

For starters, I haven't seen any evidence to show that nitrogen plays ANY role in actually making plants more freeze resistant. Nitrogen supports new growth, makes shoot growth longer, leaves larger, etc. But in plants that are healthy and well fed anyhow, it does not STIMULATE new growth, that is, causes bud break, or subsequent shoot growth after mid season.

Let me back up a back and explain how this works. In most deciduous temperate climate woody plants (those that go dormant in winter), the growth period of the plant is genetically predetermined and can be altered only slightly. A healthy plant that has been fed normally will usually put out SHOOT growth until mid season, ending usually in the month of July when another phenomenon takes place called budset. For shoot growth to occur the terminal bud forms a leaf and shoot from the leaf axil. At the next leaf, the same thing occurs; a bud never fully forms at the end, but rather continues to expand forming nodes. The number of nodes (leaf positions) formed depends on genetics, environment, and the health and nutrition of the plant. In unhealthy, poorly fertilized plants, a bud in spring may open only to a single leaf without any shoot formation at all (this also often happens to the buds behind the terminal bud in healthy plants too). Over the years, you can see this as a succession of bundle scars just behind the terminal bud; there is no branching and no ramification.

In normal healthy plants, shoot growth will stop in mid season, and the terminal bud will begin to form and harden (often changing color) rather than continuing to open. It has in essence begun the dormancy cycle, but it is not yet irreversible. Leaves on the plant continue to photosynthesize, but no new leaves form. The plant remains in this state until fall when the leaves senesce. For some species there is a bit of late fall growth from a few terminal buds opening, but not a significant amount of new growth. Late season nitrogen feeding has no role in changing this scenario. It will not stimulate new growth. If the plant is a bit deficient in nitrogen, it will take it up and store it for spring. Depriving the plant of this storage means that you will  be trying to feed the plant nitrogen in spring when it is difficult to take it up due to cold soil temperatures.

So what does upset budset and cause late season growth? If a plant is severely deficient in nitrogen all season and has not grown its genentically predetermined amount, it may break buds and extend shoot growth in late season if finally feed nitrogen. It is simply trying to catch up, and the result may be early winter kill of new growth at frost. If you feed at all during the season, this will not occur. BY FAR THE LARGEST FACTOR AFFECTING LATE NEW GROWTH IS PRUNING. Pruning off the terminal buds after they have set in midseason will very often release the dormant buds behind them on the branch. The harder you prune, the more of this late season new growth you are going to get, and the higher the risk of early frost damage. So, pushing your plants too hard, trying to do too much too late in the season, is the most dangerous thing you can do. Minor pinching here and there probably won't make any difference, but by and large, you just need to leave your plants alone after mid season. They have done their work, don't mess with their internal clocks.

Plants left alone harden off by themselves; they don't need any help. The factors above and the colder, shortening days begin a process that causes the the leaves to senesce (go to sleep) and finally fall off. Sugars, nitrogen, carbohydrates are withdrawn from the leaves as this is happening and stored in the woody tissues. Shorter days and colder temperatures trigger the plants to shed water in their cells and form longer chain sugars and carbohydrates that act as a kind of antifreeze to keep the cells from freezing internally. You shouldn't protect them from freezing, but deliberately let them freeze, several times during this process, but not allowing them to fall much below about 28F the first few times. Hardening off is a gradual process and will take several to six weeks to occur for full freeze resistence. Until full dormancy is achieved, it is imperative that you don't prune the plants, or the process can be reversed and new growth may occur. After full dormancy is reached, usually a week or two after leaf drop, pruning can occur if appropriate (another subject).

Many people think that non nitrogen fertilizers enhance this process, but there is really no good evidence to show that this is really true, and if there is an effect, it is marginal and probably a waste of very expensive fertilizer.  All you really need to do is to feed normally the entire season and avoid mid to late season pruning, then let nature do its job by exposing them to gradually increasing colder temperatures over a period of about six weeks.

Brent

Comments

[bob]

another myth busted!

[Chris Johnston]

Brent,

Thanks for all you do, and especially for bringing some sanity into some of the discussions we hear. It's amazing what a little botany and horticulture study will do!

[Graydon]

Nice read Brent. I have never bought in to the no nitrogen fertilizer but that is because I refuse to have another type fertilizer on the shelf. Your article did remind me how much I miss being up north for winter's onset.

[Patrick Desnoyers]

Thank you Brent,

I was one that search for 0-10-10 in late summer and fed my tree's that "potion" till Ive stumbled across one of your fertilizing article on evergreengardenworks.com . You have push a little farther your explanation in this post.

[Scott]

Brent,
Just a quick question, is there any way the nitrogen can be stored in the cells until spring? I use 0-10-10, and usually start around this time of year using it. As a supplement more than anything else, and usually once a week,but still using it. I'm after the root fortification. Thanks,
Scott

[Brent]

Scott

Absolutely. Winter storage of nitrogen is one of the beauties of feeding normal balanced fertilizer in the fall and early winter. Dr. Alex Shigo talks about this for forest and landscape trees, but the same is true for container trees as well. I think I have noted somewhere on the site or in the blog that maximum winter storage of nitrogen is preferable to spring feeding because it is diffiucult for trees to take up nitrogen in spring due to cold soil temperatures.

Brent