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Phosphorous/Magnesium Deficiencies?

Posted by stakedtomatoes PNW Z8 (My Page) on
Tue, Jun 23, 09 at 1:30

Hello there fellow tomato growers,

This is my first year where I'm growing tomatoes in earnest and have been trying to do everything by the book and have learned a lot from this forum. I have some tomatoes in SWC and some in the ground. Overall, the plants are doing well in that they are large and are setting ample amounts of fruit. I have Pineapple and Brandywine fruits growing so I must be doing something right.

However as of late many of my plants are showing signs of stress in what looks like phosphorous and magnesium deficiencies.

I think the phosphorous deficiencies might be due to the colder weather we've had of late. The last two weeks haven't been particularly warm and the nights have been in the low 50s and the humidity has been high. Lately, I've noticed most of the plants in the ground are showing purple new leaves and purplish upper stem growth. When temps were warmer I didn't notice this as much but the plants recently went through a major growth spurt and fruit set.

Secondly, both the plants in the ground and in the SWCs have what look like chlorosis in some of the larger, lower leaves with veins that remain green which would appear to be a lack of magnesium. (from what I've read and pictures - this makes the most sense) The plants in the containers seem to have this condition on more of the leaves than the ones in the ground.

My question is what should I do to tackle the magnesium defiecency and whether I should do anything at this time for the purple leaves? I'm afraid if I apply a phosphorous fertilizer that this may make the magnesium deficiency worse. (I read that high amounts of phosphorous make it harder for the plant to absorb magnesium) I've read about foliar sprays with Epsom salts but worry about spraying the plants with salt. Has anybody used this technique to resolve magnesium deficiencies? How about spraying with a magnesium chelate?

Any thougths on this would be welcome.

Thanks much.

Follow-Up Postings:

RE: Phosphorous/Magnesium Deficiencies?

Cold weather can cause purpling, deficiency or not. Don't worry about it.

RE: Phosphorous/Magnesium Deficiencies?

Epsom Salt is magnesium sulfate, not like table salt, which is sodium chloride.


RE: Phosphorous/Magnesium Deficiencies?

Thanks for the clarification on the Epsom salts. Should I do a foliar application?

Here are some photos of what looks like deficiencies. I think the magnesium deficiency needs to be addressed.

Hopefully, these photos will post as this is my first attempt at posting pictures.

Here is a link that might be useful: Photos

RE: Phosphorous/Magnesium Deficiencies?

I'm also growing in containers and in the ground. About half of my container tomatoes show similar signs of mg deficiency (least that's what I assume it is, the bottom leaves are exactly like your final photo). Many of my tops are more purple with rolled over leaves and purple veins. So I'd be curious to hear other suggestions.

I've been spraying with epsom salt and liquid worm casing for a couple weeks. It hasn't seemed to help. *shrug* Of course, maybe it'd be worse now without. Next year I'll be adding some Epsom salt to the soil mix. Wish Raybo was still posting. I believe he has an ongoing experiment with this?

Strangely, it does seem to depend on the plant. Anna's Russian, Black Krim, Krijna Oxheart, and Knin have it bad. Stupice, Brandywine, Cherokee Purple, Persimmon, Sungold, and Coustralee have little or no sign. All are in SWCs with identical soil and additives.

RE: Phosphorous/Magnesium Deficiencies?

Okay, I figured out how to post the photos directly into the message:

Purplish new growth with mottled leaves:

Mottled New Growth

Purple stems

Purple Stems

Mag Deficiency

Mag Deficiency (SWC - Pineapple)

Should I try to correct these by giving them a balanced fertilizer and Epsom salts?

Any thoughts?

RE: Phosphorous/Magnesium Deficiencies?

I would dissolve a teaspoon of Epsom salt in a gallon and water the plant(s) when they need more water. You may have an over-watering issue due to the yellow in the leaves of the last pic.

I would also spray the foliage with a seaweed/fish emulsion fertilizer.



RE: Phosphorous/Magnesium Deficiencies?

Thanks everyone for the input. I will let the soil dry out a some before adding any more water and then apply the Epsom salts and a Seaweed/Fish emulsion fertilizer. Hope it's not too late for the potted tomatoes as the upper leaves are starting to look like the those in the last picture.

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