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Basic question about plant science...

Posted by Ellen_inMo 6 (My Page) on
Thu, Sep 9, 04 at 18:09

Hi, I am new to this forum, although I do have posts on the Professional forum, which introduces more about me. I wasnt sure to ask my question there or here, each could probably answer my question with ease, but I thought since it was a scientific question, it may be best to post here.

I am a grower, an amateur grower, using grow lights in my home. I do not have a greenhouse, but I have a pretty impressive system that I use; or rather, impressive to me without having high tech equipment. My goals are the same as any professional grower: high yields, uniform growth. I dont just grow plants (seeds mostly) in hopes of getting a plant here and there, I want as many as possible! I have been doing this for several years, and am very passionate and obsessive about learning the best techniques for producing superior plants, with what I have to work with. Also, before anyone suggests this, I am a horticulture student, but I am part time and I have many prereqs before I get to the classes I want, so it will take time to get these questions answered by formal eduation. Since I will begin doing my own sales next year (only to friends and family), I need many questions answered.

I have been doing a project all summer with annuals. I have seeded them, and then transplanted them to different size containers to monitor growth and development. I totally expect plants in bigger pots to do just that: grow bigger, but I didnt expect the difference to be so immediate. I currently have Celosia, Geraniums, and Zinnias, with several plants in cellpacks, several in 3 inch pots, and several in 4 inch pots. What I am noticing is, within about 10 days, I see an immediate difference in plant size. The 4 inch potted plants are already bigger, wider, and more growth at the base than the cell plants. Now, I understand that these plants are getting more light, more room for roots to grow, but what I dont understand is how this can happen so immediately. I mean, my transplants were all exactly the same size when transplanted, about 3 sets of leaves each, same amount of roots. All plants are transplanted into pots (sizes I already mentioned) that have an abundance of growing medium for those one inch tangled roots to expand. How much do these roots actually grow in 10 days to 2 weeks to make such a noticable difference??

I have also noticed that, even the tiniest of baby seedlings planted in cell packs tend to grow taller than plants in the bigger pots. I must mention, these seedlings are no where near touching each other in the cells, what is making them grow up taller? I must stress that I take extreme care of my plants: they are watered precisely at the right time, and my grow lights are always the same distance from the plant,no matter what size the plant.

I guess what is baffling me is, it appears as though the pot size is directly causing these differences in plant growth. Can anyone explain why?

Again, I must stress that this is immediate differences, I am not talking about differences after several weeks. I would certainly expect a larger plant after about 4 weeks! But this is happening immediately.

I very much appreciate your input! I have some photos, I will post them here to demonstrate later today.


Follow-Up Postings:

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RE: Basic question about plant science...

Annuals, in particular, grow very fast, esp. if growing conditions are good! When I worked in a greenhouse, I remember someone not wanting to buy six-paks of tomato plants, because they were too small. They wanted the 2 quart plants which we sold out of. We said there would be more next week, and they agreed to come back. Later that day we moved a bunch of the six-pak plants into larger containers. After a week, they were MUCH larger and a happy customer purchased several at about 6 times the price of the smaller plants, which would have been equally large if he had bought them and planted them out the previous week. Larger pots give a chance for more natural, uninterupted root growth and a quickly larger plant. Enjoy growing!!!


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RE: Basic question about plant science...

I just asked my former greenhouse employer this question, taking some examples along to demonstrate, and she explained that plants in smaller pots-their roots will actually dry out before roots in the larger pots will (whether I realize it or not)and when the roots begin to dry like that, the plant will stop growing. Whereas, the larger potted plant has not dried out, and continues to grow. Apparantly, it takes some time for the smaller plant to begin growing again, after it has had this "dry spell"??

Okay, now I make sure my plants are watered when they need it, but apparantly, it must begin to dry out all around the edges of that pot, just as terra cotta pots dry out very quickly. This would make sense to me. I mean, the plants look perfectly fine, but there is some drying going on inside the pot, around the edges.

Can anyone elaborate on this??

I would think this knowledge would be vital to anyone growing plants, to know exactly what size pots to use for what plants. However, you see the exact same size plant growing in all different size pots for sale in nurseries, and apparantly will reach different size growth based upon their conditions when being transplanted. I mean, if you choose to put all seedlings directly into cell packs, from my observation, the plants will grow tall, upright, and rather skinny. I have grown cell plants forYEARS, and used them in all my gardening needs, and they have been fine. This year, I started taking some of those cells plants, transplanting them again into 4 inch pots once they got so big, and the leaves were touching. BUT, what I am examining is, putting them into the cell packs rather than the larger pots causes an entirely different kind of growth. Wouldnt this difference in growth cause the plant to continue growing "differently"??? I mean, a tall skinny transplant is not getting as filled out as the transplants in larger pots; wouldnt this cause an irreversable difference in the two plants??

I know that plant get pinched to cause them to get busy. I pinch the center stems at a certain height. But on the plants in the larger pots, this doesnt even seem necessary, they appear to bush out on their own.

I am also curious what effect using a way too big of a pot will do for a seedling. I mean, will it just continue to grow and grow uninterrupted? I would think too large of a pot compared to a tiny seedling would have major moisture fluctuations in the pot. But I am no expert, that is why I am here asking you!

I would like to understand this from a scientific perspective, like how the roots function in this. I think it is valuable information.

Thank you!


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RE: Basic question about plant science...

I believe there is more to it than just moisture fluctuations. You could technically set up a small pot with an overgrown plant which is watered with dissolved fertilizers every 10 secs with automatic watering, or you can let a plant in a large pot go fairly dry. The result will still be a larger plant in the larger pot.

I believe it has to do with hormones being activated when root meristems meet obstacles. If you plant a begonia in poorly draining, very moisture retentive soil ("clay") in a 10" pot and you plant the same type of begonia in a high quality planting mix. The result is predictable.

Obviously, the begonia planted in well aerated mixture will experience larger root growth due to water, air, and permability is present.

As you may recall, Auxins and Cytokinins are running a closed loop and balancing the growth of the plants. As long as there is a balance, growth will be rapid. If either top or root growth is mechancially stopped, the plant will adjust the other end of the plant accordingly to achieve balance. Therefore, as long as roots have optimal growing conditions (good mixture of aeration, water, fertilizer, etc) the hormones will instruct the top to grow. If the roots are stressed from being root bound, swings in fertilizer, oxygen, or water availability, top growth will also be stunned.

This is - if not obvious - then logical. The plant must make sure the top growth is kept in check with root growth. Otherwise it would prove fatal to the plant. I believe hormones are the main regulator in this respect.

Here is a link that might be useful: plant hormones - article


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