Urea Foliar Spray to Address Nitrogen Deficiency in Container-grown Avocado

[z_willus_d]

I have three several year old Avocado trees growing in large food-grade barrels cut three-quarters up.  Leaves on the trees almost always (regardless of season) look a pale unsightly color that ranges from brown (dying) to yellow to lime-yellow-green.  The pics here what the plants look like at their best, which ain't that good.  I've contemplated reasons for the leaf heath, considering the containers and root-binding, relatively cool temperatures in the winter season (though these are cool-hardy Mexican varieties), damping and/or root-rot in the container, and finally nutrient deficiency.

I was thinking about hitting the trees with several, sequential foliar sprays of low biuret urea (similar to what folks use on citrus).  This is done in the industry apparently.  But as I was researching this idea, I came across the following articles, which seem to suggest there is limited benefit to Urea foliar applications on Avocados.  The fruit production was nearly halved (vs. control) in one of the varieties as well.

I'm curious if others on this forum have contemplated this question?  Also, what do folks recommend to give a deficient tree a heavy blast of N to green-up the leaves.  Assuming, you agree that N-deficiency is in play here with these three trees.

Thanks!

http://www.avocadosource.com/arac/sum_1990/sum_1990_pg_15-16.pdf
http://www.avocadosource.com/Journals/FSHSP/FSHSP_VOL_110_PG_136-138_1997.pdf

[z_willus_d]

Oh, I wanted to note that one of the pictures clearly shows the die-off from cold damage on the flowers of a Fuerte tree (the middle tree).  Many of the flowers survived, but about half did not.  This picture was taken a month or so back.

[Cookie Monster]

why not just give it some slow release osmocote with minors.

[z_willus_d]

As for the Osmocote, that's exactly what I've been using.  The plus bags from Amazon.  I've read that a Avocado tree requires literally pounds of N in a year, so perhaps that slow release Osmocote isn't enough.  Also, it requires heat and some moisture to work, and it's been relatively cool and watering has been via rain vectors lately.  I'm thinking I need a one-time N-infusion on these trees.

[spaugh]

Your trees look pretty good to me but I am on a cell phone again.  They look pretty maxed out size wise for their containers.  Fuerte for sure is not going to be super happy in a pot.  They really want to grow huge.  What are the other types?

For fertilizer, instead of giving urea, try using a balanced fertilizer made for avocado and citrus.  Soil drench or foliar with disolved urea will surely give them a boost but thats not a good long term solution.  You are better off getting some grow power 8 6 8 or similar avocado food and get the trees on a regular feeding schedule with that.  It will work better than the osmocote if you are diligent and feed every month or 2 a small amount during the hot season.  Your trees are not large enough to need a ton of fertilizer but because they are in pots they will want regular feeding.  Based on your recent posts and all the work you have been doing, regular feeding should not be a big deal for you. 

For my in ground trees (and potted baby trees) I go out every few months and pitch a few handfulls of gro power onto the mulch and water it in.  Its pretty painless and I have good results.

[Dylan SB]

When I had potted avocados I had good results using Osmocote plus as a base then using liquid fertilizer with micros especially Iron and Zinc.  If you use a nitrate based Nitrogen source it should work better in cooler weather than ammonium or Urea.  Some of the discoloration could be due to frost of cold damage.  Your leaves seem large enough that it may not be Nitrogen that they are lacking.

[barath]

Is your water alkaline (like most water sources folks use) or neutral?  Because you might go with the tried and true acidifying fertilizer -- Lilly Miller Rhododendron fertilizer -- seems to work well for avocados and citrus, better than stuff that is labeled avocado and citrus fertilizer.  I normally use coffee grounds, but since these are in containers you can't really add the quantity of coffee grounds required.

[z_willus_d]

Your trees look pretty good to me but I am on a cell phone again.  They look pretty maxed out size wise for their containers.  Fuerte for sure is not going to be super happy in a pot.  They really want to grow huge.  What are the other types?

For fertilizer, instead of giving urea, try using a balanced fertilizer made for avocado and citrus.  Soil drench or foliar with disolved urea will surely give them a boost but thats not a good long term solution.  You are better off getting some grow power 8 6 8 or similar avocado food and get the trees on a regular feeding schedule with that.  It will work better than the osmocote if you are diligent and feed every month or 2 a small amount during the hot season.  Your trees are not large enough to need a ton of fertilizer but because they are in pots they will want regular feeding.  Based on your recent posts and all the work you have been doing, regular feeding should not be a big deal for you. 

For my in ground trees (and potted baby trees) I go out every few months and pitch a few handfulls of gro power onto the mulch and water it in.  Its pretty painless and I have good results.

Hi Spaugh, I've been topping these trees pretty heavy every year just before flowering if there's no freeze in the forecast.  The Fuerte is particularly monstrous.  I feel bad doing it, and I've read the root systems will reduce commensurate with the top growth removed, but I have to try to keep the trees to size.

You asked about the other two trees.  Those are Bacon and Mexicola - nothing fancy here.  You noted the trees don't look too bad, and from those pics, I would sort of agree with you.  However, they are looking worse now (more yellow).  I'll look into the fertilizer you mentioned.  I feel like a foliar spray could help, but is Urea the right answer.  Those research papers were interesting to read.  I found a few others that suggested that spraying Urea before a freeze imbued the treated Avocado tree leaves with some kind of protection.  That could be useful, if applicable, here in 9B.

[z_willus_d]

When I had potted avocados I had good results using Osmocote plus as a base then using liquid fertilizer with micros especially Iron and Zinc.  If you use a nitrate based Nitrogen source it should work better in cooler weather than ammonium or Urea.  Some of the discoloration could be due to frost of cold damage.  Your leaves seem large enough that it may not be Nitrogen that they are lacking.

Keep the Urea away from heat due to the biuret, right?  I have an Iron Zinc liquid amendment (from HD).  I can try applying that monthly.  I've got loads of high-end organic ferts that I use for the veggies.  I could give those a try too.  But they're all pretty low N, and not cheap.  --thanks.

[z_willus_d]

Is your water alkaline (like most water sources folks use) or neutral?  Because you might go with the tried and true acidifying fertilizer -- Lilly Miller Rhododendron fertilizer -- seems to work well for avocados and citrus, better than stuff that is labeled avocado and citrus fertilizer.  I normally use coffee grounds, but since these are in containers you can't really add the quantity of coffee grounds required.

Hi Barath, I read somewhere that the initial ph drop one gets from Coffee grinds is reversed in the long run.  Their acidity is not high enough to overcome the medium.  Something like that or to do with the carbon breakdown.  At any rate, I still do like to use the grinds in my worm bin as well as an amendment here and there - not so much for meaningful pH movements.

I do have a fancy pH meter and I've generally found our water to be just under 8, so yes it's a bit alkaline.  I do worry what the long term impact of that alkalinity will be, so in my garden beds (used for veggies), I tend to throw in a bit of soil sulfur each year to try and counteract with the water.  I haven't done this in any of my containers, save for the blueberries, for fear of overcompensating.  It not a bad idea though.  I should try and take a pH measurement.  Maybe they're off.  I'll do that.  -- Thanks!

[barath]

Is your water alkaline (like most water sources folks use) or neutral?  Because you might go with the tried and true acidifying fertilizer -- Lilly Miller Rhododendron fertilizer -- seems to work well for avocados and citrus, better than stuff that is labeled avocado and citrus fertilizer.  I normally use coffee grounds, but since these are in containers you can't really add the quantity of coffee grounds required.

Hi Barath, I read somewhere that the initial ph drop one gets from Coffee grinds is reversed in the long run.  Their acidity is not high enough to overcome the medium.  Something like that or to do with the carbon breakdown.  At any rate, I still do like to use the grinds in my worm bin as well as an amendment here and there - not so much for meaningful pH movements.

I do have a fancy pH meter and I've generally found our water to be just under 8, so yes it's a bit alkaline.  I do worry what the long term impact of that alkalinity will be, so in my garden beds (used for veggies), I tend to throw in a bit of soil sulfur each year to try and counteract with the water.  I haven't done this in any of my containers, save for the blueberries, for fear of overcompensating.  It not a bad idea though.  I should try and take a pH measurement.  Maybe they're off.  I'll do that.  -- Thanks!

I had read that as well, but I've found that in the really large quantities of coffee grounds I use they seem to work remarkably well and are much longer lasting in effect than commercial fertilizers.  But yeah, for a container planting it won't work, so I'd go with a rhododendron fertilizer like the Lilly Miller.

[z_willus_d]

I'll take pH measurements this weekend, and if the grow medium and soil seems high, I'll grab a bag at the local HD (they're cheap).  Thanks.

[Cookie Monster]

Avocados are generally averse to city water, probably due to the chlorine?

If you use a peat-based potting mix, there is probably enough buffer capacity to allow you to water with high pH water for years without issue. For example, I've been using canal water (laced with loads of calcium carbonate) for years on plants in the same peat-based mix, but pH is still well below 7.

But it's worth noting that avocados don't make the best container specimens. They will probably do well initially, but once they max out the container with roots, they will start to decline a little. I haven't done a lot of container culture, but if this is your long term plan, my guess is that you're going to need to root prune periodically.

[z_willus_d]

Hi, I live in the Placer county water region.  I've been told that the water is actually quite good.  I just measured it at around a pH of 8.

Here's a report I found:
https://pcwa.net/assets/doc/services/water-quality/consumer-confidence-reports/colfax.pdf

There is chlorine, but they indicate that it's on the low end of the spectrum for bacterial control.









 

[z_willus_d]

If you use a peat-based potting mix, there is probably enough buffer capacity to allow you to water with high pH water for years without issue. For example, I've been using canal water (laced with loads of calcium carbonate) for years on plants in the same peat-based mix, but pH is still well below 7.

Yep, I originally mixed the grow medium to be ~1/3 peat-based.  I just finished pH measurements of the three trees.  They seem to be in the right ballpark: ~6-6.5 pH.  I think I can rule out the pH as a source of problems.

But it's worth noting that avocados don't make the best container specimens. They will probably do well initially, but once they max out the container with roots, they will start to decline a little. I haven't done a lot of container culture, but if this is your long term plan, my guess is that you're going to need to root prune periodically.

I'm certain you're dead on that Avocados and containers are a self-limiting combination.  I really have no way to lift the trees (or even drop them to the ground) at the size/weight they're at.  I can only do my best to limit their size and optimize what's possible.  I sure would like to see one of the trees hold a fruit through to maturity.  It seems like that should be possible, but perhaps I'm pushing the wrong rock up the wrong hill.  If folks agree it's not hurtful (and possibly helpful in the short-term), I"ll plan to hit the trees with a Foliar spray of the Urea (+ surfactant) and follow-up with regular fertilization (Osmocote+, the Lilly Miller Azalea Food, or similar.  I'll also hit the tree with an iron/Zinc foliar.
Thanks for all the advice.

[barath]

One theory I have is that some rootstocks are slow enough growing to be appropriate for a container, such as Duke.  Since you're in Roseville, you might make a trip to Oroville to get some Duke seeds later this year when they're in season and start them as rootstock.  They're super cold hardy and root rot resistant, and also seem to be quite slow (and steady) growing, and might produce a smaller tree even when grafted.

[spaugh]

Or choose smaller varieties.  Those 3 types you have in barrels are avocado weed trees.  Smaller tree like wurtz, holiday, pinkerton, and maybe even Reed would be better for container growing. 

[Mark in Texas]

Yeah, those barrels aren't going to cut it.  The profile of a good pot for avocados would be very wide, one reason I go with RootBuilder.  I can control what I'm making. 

Peters 25-5-10 and DynaGro Foliage Pro, 9-3-6, would be my choice for trying to correct a N deficiency.  The Peters has a good N ratio of ammonical to nitrate, something many do no consider.   Your N deficiency can also be induced by a cramped root system.  Mulching is also a must whether you're in ground or for pots.

100 gal. pot Reed tree.  (recovering from a freeze)  I maintain that tree at 10' and it will produce up to 100 fruits/yr.

[z_willus_d]

Those avocado tree "weeds" are about all you can find to buy in the nurseries up here in N. CA.  I was pretty clueless about avocado tree culture when I purchased them several years back.  I also was clueless about container culture, particularly vis-a-vis avocado tree needs.  I was using these same containers with some success for my citrus, so I extended the approach to Avocados.

Mark, if I could muster the strength of Samson, I might be able to topple the barrels and repot in RBII containers.  Maybe I'll give it another try after seeing if they're able to set any fruit this season.  I think I would heavily damage the trees.  I'd like to ultimately do a lot of top-working on the trees.  I'm not sure if the best way to do that is to fully decapitate the trees and wait for water shoots to which the scion wood is bound, or if I'm better off using existing tertiary branches and the like.  Also, were one to perform a decap, what would be the best time to do so so as to align the assumed growth with the availability of scion buds.

[spaugh]

What I mean by avocado weeds is they grow like weeds.  They are good cultivars but giant size tree.  I am growing all those types and they really want to get big.  Here's a 15ft tall bacon tree that's 2 years in ground from a 5gal pot.  I've topped it several times but now I give up.  It just wants to be huge so I'm going to let it.

This time of year is not a bad time to do the decapitation by the way.  Flower g should be about done and plants should be flushing. 

By the way, I grew up near there in stockton.  We used to grow a lot of citrus and stone fruits but never avocado.  You are doing pretty well for how far north you are there.