How plants eat

Wynona(z4ID)July 27, 2004

What, when, and how to fertilize my plants is always a dilemma to me. I have an image in my mind of little plant roots slurping up their dinner. I know enough (just enough) that I understand there is a chemical process going on at root level. Is it possible to explain this in laymen's terms so that I will know what I should be fertilizing with at different times (for example: seedlings, plants in bloom, perennials that have flowered and set seed, getting ready for a long winter's nap)? It has been 25 years since I had chemistry so please be gentle.

I'm really excited about this forum. Thanks Spike.

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BradleyQT(z5 Westminster/Broomfield)

Now Spike...

You do know that the plants make their own dinner. Such is the wonder of photosynthesis. Sunshine + CO2 = dinner. Pretty amazing stuff if you think about it.

When you feed your plants, you are giving your plants the components they need to either support the photosynthesis process or support other processes like that might help you out such as growth or fruit production.

We could go through it all here, but I think there's a really great site for the non-chemist (and kids) about plant nutrition.

Obviously the key to providing plants with macro & micronutrients is the same thing as feeding yourself.

If you think of nutrients as having a recommended daily allowance, you won't overfeed.

Overfeeding on a small scale is simply wasteful (plus some plants won't "like" it). On a large scale, over-fertilizing is a pretty big problem

Just some fun factoids:

All organisms (plants & humans alike) use ATP as their major form of cellular energy. The TP in ATP means Tri-Phosphate. So you can see that phosphate might be an important chemical for organisms that are using a lot of energy (whether tomatoes or you). Processes that are energy intensive (like blooming or growth) will need more phosphorus.

Plants use Nitrogen to make amino acids. Amino acids are put together in chains to form proteins. Proteins make up most of the structures in both our bodies and plant cells (though plants do have those cool sugar walls).

Those proteins form both chlorophyll (where plants produce all their food) and mitochondria (where plants turn that food into energy).

Chlorophyll is green, so more nitrogen = more chlorophyll = greener plants (to a point). Also, more nitrogen = more mitochondria = more energy production.

Again - see the note above about overfertilizing. You don't want to give any plant too much of any nutrient.

Also, the only way we get nitrogen to make all the protein in our bodies is by either eating plants or eating animals that ate plants.

Getting nitrogen out of the ground is really a trick. Check out this link for more info.:
http://www.ncagr.com/cyber/kidswrld/plant/nutrient.htm

Finally, Potassium.

Potassium is used in something called the sodium/potassium pump. The sodium/potassium pump helps cells transport nutrients and other stuff across the cell membrane. Once again, potassium is just as important for you as it is for the plant.

Here is a link that might be useful: Plant Nutrients for non-chemists

    Bookmark   July 27, 2004 at 3:21PM
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Wynona(z4ID)

Thanks BradleyQT, this is what I'm looking for. Your expanations are easily understood. You will make a great teacher. I have saved the kids site for future reference, too. (BTW, I'm Lisa, I was thanking Spike for this site. Sorry for the confusion.) Thanks again.

    Bookmark   July 27, 2004 at 4:20PM
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froggy(z4/5 WI)

as a side note;

one of the reasons greenhouse plants and golf course greens are always so beautiful is they are constantly given a micro dose of fert's. almost like the hydroponics ideal of enough food, just when u need it.

froggy

    Bookmark   July 27, 2004 at 5:13PM
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Dorie_in_Alabama(7a)

Another thing to think about. These minerals and elements enter the plant system as a dissolved part of the available water. Transpirational pull from the stomatal openings create the 'suction' through the xylem vessel system from the leaves all the way down to the root hairs. Absolutely no energy is exerted by the plant during this process, an amazing thing when you know that a mature deciduous tree with its root/soil system in tact, will take up about a ton of water per day in this process of transpiration.

    Bookmark   July 28, 2004 at 10:45PM
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Wynona(z4ID)

Wow, this is a lot for me to digest. (Silly pun intended.)
Froggy, would I be correct in assuming that it would be beneficial to fertilize my container plants that have to be watered daily with a dilute solution of Miracle-Gro? (Maybe once a week?)
Dorie, That is pretty amazing. I will look at our huge old cottonwood with a little more respect from now on.

    Bookmark   July 29, 2004 at 10:32AM
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BradleyQT(z5 Westminster/Broomfield)

Dorie -

Just wrote a lesson plan on transpiration for a class. It's absolutely the coolest process!

Cool correlations between the dampness of human aveoli and the dampness of the plant cells. Also how transpiration is "sort of" like the plant's circulatory system (transport nutrients and allows for gas exchange).

I presented it in one of my ed. classes and it was fun to stump the other science teacher types with statements like "plants have lungs". Obviously, they don't have a lung structure, but they must have gas exchange. (Drowning our favorite houseplants is a very common way of loving plants to death).

Cool (very technical) article on how transpiration is thought to be related to the fact that trees will grow so tall...and then no taller.

Here is a link that might be useful: What limits the heights of trees?

    Bookmark   July 29, 2004 at 11:30AM
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kdjoergensen

Think of fertilizer as building materials or raw materials which goes into the manufacturing process.

The manufactuering process is photosynthesis (as explained above).

You fertilize when the draw on carbohydrate (stored energy) is highest AND when plants have best possible conditions to photosynthesize.

E.g. in late spring, many perennials put on lots of growth and correspondingly need to synthesize lots of tissue which require "building materials". As the plants goes into summer, they have 'matured' in the sence that new leafy growth is significantly less than in spring (for most perennial plants) and therefore the need for fertilizer for growth is less.

In summer, cool season plants like pansy, kale, cool season grasses, etc also stops photosynthesizing almost entirely due to warm temperatures. Fertilizing at this time will prompt growth, but since the plants can't produce energy (foodstuffs, e.g. carbohydrates) they must pull on stored reserves in the roots. This can weaken the plant and worse case deplete resources.

Summer annuals which continue aggressive growth in summer may have a need for continued levels of fertilizer, however.

Therefore, fertilizer should be timed based on the type of plants (perennials, annuals, cool season vs warm season) and it is usually a good idea to get an overview of the two factors:
a) when does the plants consume most carbohydrates
b) when does the plants have optimum photosynthesis conditions

if a+b can be combined, you are usually safe. If a) happens during times when photosynthesis is not feasable (due to hot temperatures, etc) then fertilize according to b) only.

    Bookmark   July 30, 2004 at 3:04PM
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froggy(z4/5 WI)

what im saying is that pro's have done their homework and thru practice and trial and error, they have a formula.

i dont know ur situation. just tellin ya the facts of some growers.

froggy

    Bookmark   July 30, 2004 at 6:26PM
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maineman(z5a ME)

Kenneth,

"In summer, cool season plants like pansy, kale, cool season grasses, etc also stop photosynthesizing almost entirely due to warm temperatures. Fertilizing at this time will prompt growth, but since the plants can't produce energy (foodstuffs, e.g. carbohydrates) they must pull on stored reserves in the roots. This can weaken the plant and worse case deplete resources."

Does it follow, conversely, that warm season plants stop photosynthesizing almost entirely at cool temperatures and that fertilizing them during cool weather will prompt growth, but sap stored reserves from the roots?

Could the needed carbohydrates be supplied by foliar feeding the cool-stressed warm-season plants with a sugar or sugars (sucrose, dextrose, something-ose) or some other organic substance(s)?

MM

    Bookmark   August 27, 2004 at 4:45AM
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Rosa(4ish CO Rockie)

MM asks, ....Does it follow, conversely, that warm season plants stop photosynthesizing almost entirely at cool temperatures and that fertilizing them during cool weather will prompt growth, but sap stored reserves from the roots?

Yes, actually it does and this is the reason that grdeners do not fertilize near the end of the growing season. It's also the reason that fall herbicide applications work so well-plants are drawing down the little energy they're making into the roots in perperation for making it thru dormant times and having the energy necessary to regrow next year.
And no to your second question about feeding cool stressed warm season plants (sucrose, dextrose, something-ose)are not utilized like..say...giving an athlete a candy bar for additional short term energy boost.

    Bookmark   August 27, 2004 at 7:54AM
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chaman(z7MD)

From the postings so far, can we understand that plants will need enogh supply of nitrogen during juvenile stage,enough supply of potassium for pumping cellular fluids throught the life of the plant, and enough supply of the phosphate at the time of flowering and fruiting ?
At the same time what are the symptoms when the plant does not have required supply of these elements when required?

chiman

    Bookmark   August 27, 2004 at 9:26AM
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Rosa(4ish CO Rockie)

Yes, chiman however, these nutrients are in demand all the time but more of one at certain times than others.
Poor and slowed growth, poor root system developement and little or weak flowering and fruit set can be indications of low levels. But poor fruiting (or none at all) can also be attributited to high levels of nitrogen in some crops/plants. More (of these nutrients) is not always better even if occurs naturally in the environment.

    Bookmark   August 28, 2004 at 9:57AM
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chaman(z7MD)

When we over feed the plants, unused nutrients are left in the soil.At some point and time unused Nitrogen, Phosphate and Potassium may deteriorate the soil.

chiman

    Bookmark   August 28, 2004 at 10:39AM
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froggy(z4/5 WI)

At some point and time unused Nitrogen, Phosphate and Potassium may deteriorate the soil.

^^^^

ya and u have a huge increase in the 'salt' content of the soil.
balance is the answer.

froggy

    Bookmark   August 28, 2004 at 9:04PM
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kelly_cassidy(z5 E. WA St.)

A mild correction to BradleyQT's post:

BradleyQT writes: "Potassium is used in something called the sodium/potassium pump. The sodium/potassium pump helps cells transport nutrients and other stuff across the cell membrane. Once again, potassium is just as important for you as it is for the plant."

Animals (but not plants) use a sodium/potassium pump to move sugar (and other substances?) across cell membranes. Your blood has a high concentration of sodium and a low concentration of potassium. Your cells have a high concentration of potassium and a low concentration of sodium. The cells maintain this sodium/potassium gradient by using energy to "pump" sodium out and potassium in. The sodium/potassium gradient then indirectly provides the energy to move glucose (blood sugar) from blood into cells. A high dose of potassium injected directly into the blood stream will kill a person because there will suddenly be a high concentration of potassium in blood. Glucose transport into cells stops, which kills the cells in a few minutes.

Plants do not have a circulatory system like animals. Plants have xylem, which moves water between ground and leaves, and phloem, which moves a dilute sugar solution between leaves and roots, but the phloem and xylem don't reach every single cell. Short-distance, cell to cell transport of sugars is via tiny membrane tubes (plasmadesmata) that connect cells. In fact, most plants have tons of potassium, but virtually no sodium. Animals, which must have sodium, usually have to resort to finding a non-plant source for their sodium. Deer walk miles to salt licks. Porcupines will chew up a person's backpack because it tastes like salty sweat. People walk miles for a potato chip.

In plants, potassium controls opening and closing of stomates and seems to also control xylem resistance to water uptake (research is ongoing). Potassium is more of a problem for plants to get in wet climates than dry climates because potassium is so easily washed out of the soil by rain.

    Bookmark   August 28, 2004 at 11:17PM
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shadowgarden(z5OH)

So, is horse poop better than cow poop?

    Bookmark   August 30, 2004 at 11:26PM
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BradleyQT(z5 Westminster/Broomfield)

Thanks Kelly,

I googled for potassium and plants and didn't pull up any helpful sites...so I applied what I knew about animal cells to plant cells. Obviously, this is not always correct as it was in this case...though I'm shocked by the similarities/analogies between plants & animals in many cases.

As you pointed out, some times plants have their own unique cellular processes as well. Thanks for all the great information!

    Bookmark   August 31, 2004 at 5:01PM
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kdjoergensen

potassium has several uses in plants. One of the main function is regulating cell functions and it is used to tricker plant hormones. For example, the guard cells which open and close stomatas on the undersides of leaves (which allow carbondioxide in and water vapor out) is controlled by potassium ions.

    Bookmark   September 2, 2004 at 10:50AM
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kdjoergensen

Forgot to mention, it is correct that plants do not have a potassium-sodium pump like nerve and muscles in humans and animals.

Plants usually take up nutrients through the roots by osmosis (gradient transfer) but also use 'active transport' to move fertilizer ions into the roots, however. The potassium-sodium pump uses active transport, too. Maybe this is the confusion ? (sodium is not an essential element for plants).

Active transport simply means that ATP (energy) is used to run a pump to bring mineral ions into the plant.

    Bookmark   September 2, 2004 at 11:00AM
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