Okay to fertilize in extreme heat?

tempusflitsJuly 21, 2011

I've been skipping the fertilizer in this heat. Is that a good idea or no? Previously, I gave my plants a weak solution of fertilizer once a week when I water their containers. I can see pros and cons to doing that during a heat spell, so I'm unsure which I should do. Does anyone know the correct answer?

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I don't stop no matter what and I never see any ill effects.
I do if I stop though.

If the roots to your plants overheat, they won't take up fertilizer anyway. I would make it a practice to let water run through at each watering though to wash out any unused salts accumulated from unused fertilizer.

Enjoy this warm weather before fall rolls in faster than we know it.


    Bookmark   July 21, 2011 at 9:54PM
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Thanks, Mike. You're right about fall. It's close.

    Bookmark   July 22, 2011 at 6:37AM
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buylady(z5b IL)

well hi yaaa Mikieeee an all, this heat is terrible here in the 90-100's every day but plants are really enjoying the sun have a gr8 day all...

    Bookmark   July 22, 2011 at 2:25PM
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tapla (mid-MI z5b-6a)

I think it depends on how you fertilize. I do withhold fertilizer when day temps are above about 85*, unless the plants are in full shade from mid morning to mid evening. High soil temperatures cause plants to go semi-dormant, so they use only very small amounts of nutrients. The higher the level of EC/TDS (roughly the level of solubles/dissolved solids in the soil) the more difficult it is for the plant to absorb water and the nutrients dissolved in the water, so a low level of EC/TDS when soil temperatures are 80*+ is a good thing. Additionally, high soil temperatures often kill a considerable number of roots, especially on the south and west sides of containers. High fertility levels promote larger populations of the bacteria/fungi that cause root rot and can increase the likelihood and severity of that disease.

During the summer, I usually fertilize every 1-2 weeks (when temps allow) with solutions at or just above the recommended strength, even though I know frequent applications of weak fertilizer solutions like many of you are using are no where as potentially problematic as full doses. It's a time thing - I fertilize by hand & I just can't mix the solution and fertilize some 300 containers every time I water (daily); so, if you do continue to fertilize during the dog days - reduced solution strengths until soil temps are sure to remain below about 80* for most plants would be a smart tack.


    Bookmark   July 22, 2011 at 9:13PM
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That's interesting. Thank you, Al.

    Bookmark   July 23, 2011 at 7:25AM
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greenman28 NorCal 7b/8a

I do the same as Al.

I fertilize every one to two weeks, using a full dose or just a tad above (for citrus, for example).
My maples and conifers are fertilized closer to every two weeks.

Now that the temps are high, I've reduced the amount of fertilizer solution that I apply.
Same concentration, but half the volume watered into the container. As always, I'm watering
the container mix before and after fertilization.


    Bookmark   July 23, 2011 at 12:32PM
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Are there other situations when you reduce or eliminate fertilizing?

-rooting cuttings
-young plants
-planting seeds
-plants compromised from shipping/dehydration

Or any other situation I didn't think of where you shouldn't use fertilizer or should use it at a very dilute rate...

    Bookmark   July 25, 2011 at 7:03PM
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greenman28 NorCal 7b/8a

Yes -
reduced nutrients for seeds/seedling, rooting cuttings, transplants, and re-pottings for sure.
When you want to encourage rooting, use a media with low initial levels of fertility.
I hold off fertilizer for two weeks after root-work/re-potting.


    Bookmark   July 25, 2011 at 8:41PM
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tapla (mid-MI z5b-6a)

I don't fertilize cuttings until I'm sure they've rooted because of the impact solutes in the soil solution have on water absorption and the cutting's ability to remain hydrated.

I don't think there is any credible evidence that the fine roots responsible for water/nutrient uptake, once they form, are any more likely to react negatively to normal levels of EC/TDS if they're attached to newly formed roots than if they happen to be tertiary, quaternary, quinary, senary ...... bifurcations eventually leading back to older, lignified roots. I've seen newly formed roots grasping both granular and controlled release fertilizer prills/pellets as they dissolve with no ill effects on the roots or the plant proper. The work horses are ALWAYS young roots, so if the belief that newly formed roots are more fragile held water, the age of the plant would still have nothing to do with the age of the roots doing the heavy lifting.

I don't fertilize seedlings until the first set of true leaves appears. Until that time, the plant gets it's energy from carbohydrates and nutrients stored in the endosperm.

I've found that even when plants are dehydrated/wilted, I've done no observable damage when fertilizing at very low rates. I wouldn't apply fertilizer solutions at the rate suggested on the package, but the approximately 1/8 strength doses I use at every watering during the winter haven't presented any issues.

I DO withhold fertilizers when actual soil temps are likely to be much above 80*, and I never knowingly fertilize when average soil temperatures are expected to be below 55*. I also don't premix CRFs into soils I don't intend to use within a short time.


    Bookmark   July 25, 2011 at 8:56PM
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