Fertilizing is closely linked to the need for water. Plants that aren't growing or transpiring need little in the way of regular fertilizing. Still, there is no harm in maintaining an adequate supply of nutrients in the soil at all times.

I fertilize right up until plants lose their leaves, and even beyond that for conifers. Once I bring them in to overwinter in an unheated garage, I stop fertilizing until spring and the onset of notable growth. For some plants, I specifically withhold fertilizer until after the spring push is done, but that is an intentional manipulation.

The reason I don't fertilize in the winter is, I often water by tossing shovels of snow on the plants, which means the soil isn't getting flushed. If I fertilized, I would want to flush the soil to prevent salts from accumulating - it's just much easier to withhold fertilizers from plants that are dormant/quiescent/torpid.

In what chapter in Dr Whitcomb's book did you find reference to fertilizing in the winter? I'd like to review that part.

Al

Thanks, Al. Since I am flushing the soil at each watering, I may move to using 1/4-strength FP.

For some reason, I seem to recall some warning about ammonium toxicity, if (ammonium) nitrogen is applied when the temp. was below 45 *F? Is there any truth to this?

You mentioned that you withhold fetilizer from some plants until after spring push...I'd be really interested to learn more...is this a bonsai thing to increase dwarfness?

I dug through PPIC and dug up the section I had in mind. In Ch. 7 (Other nutritional and cultural considerations), the section on 'Time of Planting'. By way of context, he's suggesting potting up in the fall to prevent winter damage:

"A plant established in a container is more vulnerable to cold injury than a plant recently shifted. This is due to the presence of the bulk of the roots on the established plant just inside the container surface."

And he goes on to state that it is imperative to provide fertilizer to get the plant through the winter.

"The assumption is sometimes made that there will be enough residual nutrients in the smaller container to provide for the plant during the winter period. Unless an incorporated slow-release fertilizer was used that lasts through the winter period, the plants should be fertilized either by adding nutrients to the new mix in the larger container or by top-dressing."

And here is the key point:

"Remember that plant roots can absorb nutrients anytime of the year when temperature and other conditions are favorable. Roots do not go dormant as do the tops of many species. Therefore, nutrient absorption occurs over a much longer period than is reflected by top growth. Since it is difficult for personnel to remember to fertilize with liquids through the irrigation system during the dormant period, especially when little irrigation is required, a slow-release fertilizer, either incorporated or top-dressed, is the most practical solution."

And of course he presents data.

Tying this back into my original post, they're calling for temp's to rise to nearly 60 for close to a week, and I'm thinking of pros and cons of fertilizing, and am considering if there's any strong reason to fertilize during this period, or not to.

Best regards,
Alex

Excellent information, Alex, thanks.
Great to see you posting, too, Al. You've both reminded me to hit my outdoor containers
with some nutrient solution. We've had copious rains since October, and I know that my
pots are flushed. I'll go with a 1/8 strength dose, unless Al indicates otherwise.

Alex, from what I recall of what Al has posted in the past, the danger of ammonium toxicity
is when using Urea-based Nitrogen fertilizers in soils that are cold - less than 50F - 55F.
I think Fish Emulsion was the fertilizer under discussion at the time.

Josh

Thanks for the information, Josh. FP contains ammonium and nitrate, but no urea. I need to look up more information on ammonium toxicity...I can't think of a good reason why urea might act differently from ammonium though, in this respect. Anyway, from your post and Al's, it sounds like a low dose of FP should be okay at this time of year. I shall follow your lead and go with 1/8 strength.

-Alex

Hopefully Al will chime in on the ammonium toxicity.
It is the unused fertilizer that sits in the cold soil that leads to the toxicity.

The day after I fertilized all my outdoor maples and conifers, et cetera,
we had a half-inch of rain. So I'll hit the containers again once they've dried a bit.

Josh

I have a follow-up question:
How long does the soil need to remain above 50-55 degrees in order to fertilize (with urea based N) outside pots in the winter? For the afternoon? For a few days?

I'm new to gritty and 5-1-1 mixes. I have a yucca plant in the gritty (gypsom) and a clematis vine in a 15" pot in 5-1-1 (lime). I use all purpose MG as the fert (+epsom salt for the gritty). The plants are in full sun on a deck from about 12pm-4:30pm...

Thanks to all for sharing your knowledge!

Alex,

Thanks for starting this topic. I had no idea you should fertilize container plants in the winter. Like you, I have a few pine and other conifers in small containers, in my unheated garage. In late fall and early winter I simply add a bit of snow occasionally to the containers. The difference might be that my garage gets quite cold, and the soil in the containers is now frozen solid and has been for at least a month. More sub-zero weather is coming my way so they won't thaw out any time soon.

If the soil is still loose and able to accept water, perhaps in a warmer USDA zone, then I can see the benefits of some fertilizing in winter. However if the container soil is completely frozen I don't think it would do any good to add even a small amount of fertilizer to frozen soil.

Does that sound correct?

TYG

Beth - I fertilize often in the summer. I try to do it weekly, but sometimes I can't get to it that often because it takes about 3 hours that aren't always available. I don't fertilize when I can see by the forecast that the mean temperature (average of the highs & lows for the day) is going to be below 55* for several days in a row in the immediate. There isn't as much guesswork as you think, though. About the only time I have to think about it is during the spring and fall when weather turns unseasonably warm or cold - the rest of the time doesn't take much consideration.

YG - Yes, that's correct. I fertilize right up until the deciduous trees go dormant, then stop fertilizing both the deciduous and evergreens at that time. How you fertilize houseplants in the winter depends on your soil and watering habits, but the commonly held belief that you should stop fertilizing houseplants in winter is based on the assumption you are using a heavy soil that can't be flushed regularly. The idea that you shouldn't fertilize is someone's choice of the lesser of two evils, but still an evil. The thought is, it's better not to fertilize, which contributes to the accumulation of salts in the soil, and allow the plant to remain nutrient-starved while growing slowly, than it is to fertilize and risk the results of a high concentration of soluble in the soil solution. The best course actually is to use a soil you can flush at will and to continue to fertilize regularly at a reduced rate. That keeps a maintenance level of nutrients in the soil and available in a favorable ratio. That's a scenario difficult to improve on.

Al

Thanks, Al. That clears up things ALOT!

And thanks, Alex, for letting me piggy back on your post. :)

Al, thanks very much for the clarification. Since the pines and junipers I have in containers are currently frozen solid, there is no point in trying to worry about fertilizing. Any fertilizer I would add would simply freeze and sit on top of the frozen soil anyway.

If I was in a warmer zone Id be sure to add a small amount of weak fertilizer from time to time. However, I don't see that happening up here anytime soon. I think the high temperature for tomorrow is supposed to be about 10F.

Thanks

TYG

2* here now. -6 for tonight's low and all the way to 12* for us tomo. Coldest winter for us since I was a kid. Sorry for the OT chatter, MG. I beg a pardon. ;-)

Al

No need to beg pardon Al, it's always a pleasure when you drop in.

We got 14 inches of snow last night here in NJ. It was 4 *F this morning when I cleared the driveway and windchill of -10...

Alex

Thanks! WeatherBug says we went down to -2* last night, but my thermometer said -4 when I got up - and it's snowing here again now.

Our side streets and roads are like something I've never seen. The snow is packed into solid ice often 6" thick or more over the entire road surface. There are ugly deep ruts and potholes in the ice every few inches. There is no end to the cold in sight - no January thaw for us - so it's going to be that way for a while. I don't remember a colder winter since I was a kid.

Al

Meanwhile, here in northern California, we just broke a record for the most consecutive days without precipitation during our traditional Winter "rainy" period.....

Josh

Great thread.. I was reading this and enjoying the great info.

Night!

Laura

This post was edited by loveplants2 on Thu, Jan 23, 14 at 20:48

If you fertilize with a fertilizer that relies on urea or any other organic source of nitrogen (blood meal, feather meal, hoof/horn meal, alfalfa meal, boiled rice hulls, etc) there is a considerable risk of ammonium toxicity if soil temps are below 55-60*F or will be below 55* at some point in the near future.

Immediately after nutrients are absorbed they are deposited in plant cells. If the nitrogen is in nitrate form, this is not a problem for plants; however, if nitrifying soil bacteria are inactive due to low temps, they are unable to convert ammoniacal nitrogen to nitrate. This causes ammonium to accumulate in plant cells with a high potential to damage the cells (at temps below 55-60*F).

If you do fertilize, using Foliage-Pro 9-3-6 wouldn't be much of an issue because it supplies >2/3 of its nitrogen in nitrate form; however, most other 3:1:2 ratio fertilizers (like 24-8-16 and 12-4-8) rely completely on urea as their source of nitrogen and they would very likely create toxicity issues.

Hobby growers almost always misdiagnose ammonium toxicity and attribute its symptoms to unrelated causes. In addition to being a frequent problem when grow media are below 55-60*F, the toxicity is also extremely common in waterlogged media or in plantings with compacted grow medium and/or when roots are congested; this due to the paucity of oxygen and high levels of CO2 in waterlogged or compacted media.

BTW, if you will be keeping the chives in a pot, you should divide them every year, taking one or two divisions from the perimeter of the clump - not from the middle. The planting will need fertilizing if you keep it in a pot, but probably won't need fertilizing if planted out. Every plant needs a full compliment of nutrients essential to normal growth to be at it's best, and the only way to tell if your garden/ beds need supplemental nutrition is by way of a soil test.

Al

We're talking about chives. They're totally hardy, don't need to be in a container, don't need to be in the garage in winter and can simply be planted in the ground there they need no fertilising.