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I grew my mint plant in a pot to contain the roots, and that has worked well for 3-4 months. However, the plant is not really producing fresh leaves now. Is there anything I can do?

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2 Answers 2

up vote 16 down vote accepted

There are two reasons I can think of:

  1. Your plant has bolted

    If your mint plant has been producing flowers (usually a cone shaped inflorescence), then it has started bolting. While mints are perennials and I haven't known them to die off quickly after bolting, it sure is a process that makes the plant focus its resources elsewhere (flowers). You should take them out as soon as they appear.

    I have known my basil, cilantro and parsley plants to start growing woody stems when they're in an advanced stage of bolting and I'm quite sure that it is also the case for mint.

    enter image description here Source: Wikimedia commons

  2. Your plant is root bound

    A plant is said to be root bound when it is grown in a container too small for it. The roots fill up the volume of the container and when it cannot grow any more, the plant stops growing too. A root bound plant will not grow even if the conditions are favourable and you have a perfect watering/feeding/fertilizing schedule. Here's how the roots will look like inside the container.

    enter image description here

    Source: Virginia cooperative extension

    The article linked above puts it quite well:

    At what point do plants stop growing in a pot? It's a bit involved, but the simple answer is that new growth stops or slows when they become rootbound. So what's rootbound? Rootbound is when there is no effective space for new roots to occupy. Roots effectively occupy the entire volume of space between the soil particles. One of the first symptoms of being rootbound is, in fact, that plant growth slows despite favorable environmental conditions (light, water, fertilizer, etc). The second symptom is that rootbound plants begin having difficulty taking up fertilizer. This is undoubtedly related to the inability to form new root tissue. You see this as a chlorosis despite the fact that they have been properly fertilized.

    Given that you grew it in a pot specifically to contain the roots, I'm quite certain that this is the problem. You could try transplanting it to a bigger container to provide more space for the roots. Don't forget to untangle the bound roots before you transplant.

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6  
I agree, the problem is much more likely to be #2. Given that mint is such a vigorous plant, I always pinch out the growing tips when they reach a height of about 9 inches, to prevent it from becoming leggy and encourage it to bush out. –  Mancuniensis Sep 3 '11 at 14:47
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If is #2 should I trim it back? - and will it regrow afterwards? –  Dan Sep 3 '11 at 16:28
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Yes, you should trim back the roots, not the plant above the ground. This is an article that explains how. However, instead of incorporating it into the answer here (because it's more of a diagnosis of what's wrong with your mint), I'd recommend that you ask a new question, "How do I prune the roots of a root bound plant" and give the background referencing this question. I'll condense that article and add in some personal practices as an answer and others can contribute their answers as well. –  Lorem Ipsum Sep 3 '11 at 16:35
    
@yoda i didn't see the pruning question appear and it seems like a useful question so i've added it in today gardening.stackexchange.com/q/2968/99 –  Tea Drinker Nov 30 '11 at 12:23
    
Absolutely agree on #2. I had the same problem when I attempted to grow mint in buried pots to control its growth. I've now switched back to growing it in the ground, and just make sure to use it heavily to keep it in bounds. –  michelle Jun 17 at 13:01

By the look of it I would think it received too much nitrogen (some of the leaf tips are burnt). To remedy the situation, you can try giving it some more potassium (without adding extra nitrogen), or just stop fertilizing it and wait it out. Mint uses nitrogen fast, in my experience (so, it shouldn't take ages and ages). Potassium deficiency can result in woody stems and stunted growth. It's a popular opinion that too much nitrogen will result in excessive leaf growth, but it can also stunt a plant, in my experience.

Also, Lorem Ipsum's answer has some good insights. Mint grows roots very quickly. In my experience, mint grows much better while the roots have extra room. You could try breaking up the rhizomes and repotting a smaller portion of them in the same container, or else plant it in a larger container. It's also often a good idea to trim mint lower and let it grow back if it's getting tall and not so bushy. I wouldn't trim it if you're also going to repot it, or divide the roots.

My recommendation would be to find out if the roots are everywhere. If they are, divide the rhizomes. Trimming the roots, as one commenter mentioned, might be a good alternative option, but I don't know. After repotting (and even if you don't repot), give it some extra potassium. Not only should it help with growth and stopping further prematurely woody stems, it should also help improve chances of the plant living after having its roots disturbed so. I personally recommend potassium sulfate. Adding some rockdust or gypsum with the potassium should help it, too, if you like. (Or even putting eggshells from a boiled egg at the bottom of your container, if you want a more economical option.) Potassium and calcium go hand in hand.

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