I'm in LA so this might not apply so well. I, too, am a n00b gardener and started with spearmmint by transplant. I stuck 'em in soil and they kept dying.

Here's what has been working though: Stick them in a cup of water (which may be your jar-of-water method), but also keep them out of direct sunlight. I noticed when I put my newly-transplanted mints in the sun, they start getting wilty. When I put them back indoors, they spruce up again. I'm guessing when they're freshly cut, they can't absorb water as fast as it's being evaporated from the leaves, so avoid anything that will speed evaporation (light, heat, wind) by keeping them indoors. Also cut off some of the bottom leaves. After several weeks, roots will form (if the plants didn't die their mysterious deaths), then you can pot them. Even then, leave them indoors for a week or two so the plant can get rootier, enough to absorb water at a rate that can keep up with evaporation.

I also heard (from the internet :oP) that mints need a lot of light and water. My plants, once well-rooted, seem to enjoy the light and water.

Here is a link that might be useful: GreenItUp (in a non-gardeny sorta way)

I would guess the mint is getting a bit too baked. It is originally from temperate regions of Europe, Asia, and Africa. Can you move the mint to a location outside where it would still be a well lit location but it wouldn't be in direct sun like your patio is? Maybe on the other side of your house? Or in the shade of a larger plant that doesn't mind the sun? Or whatever, you get the idea. I think the mint is getting more heat than the it can take.

This is only a guess. I live where it snows so my concerns are usually about cold hardiness not heat tolerance.

FataMorgana

Thanks for your responses. I previously had the mint in large pots, where it died, both outdoors (sun) and indoors (overwatering). It's only in a small pot now because I'm down to a single live stalk. It's currently on an East-facing window sill, and I'm giving it a little water once a week and so far it looks OK though kind of leggy. When (if?) it gets bigger, I'll put it in a larger pot but for now I don't want to disturb the roots.

My mom has a mint plant on a north-facing window that's doing well, and she only waters it half a cup once or twice a week. One florist actually told me not to water the mint at all if grown indoors, just mist the soil a little every day! If I manage to establish more cuttings, I'll try to grow some outside on the East side of the house - I've only got access to the East and South sides.

I've also been looking up pictures of mint rust, and they show little brown pustules on the stalk. I didn't have any of those, so I'm probably just killing my plants out of incompetence.

I just don't know where this idea comes from that mint doesn't need water! If mint is to be kept in a pot it needs to be a pot twice as big as you think it will need. The soil needs good, loose, and be kept moist, but not wet. I have several plants inside that really are outdoor plants... like mint. I give them some real sun outdoors everyday.... for an hour or two. If your plant is getting leggy then cut it back by 1/2. This will encourage it to branch out and maybe even throw off new plants from it's roots. I don't imagine that Hong Kong is dry and searing hot like here so you can probably plant it in the sun outside when you get ready to do that. Also, remember that window sun can bake a plant faster than anything.

Good luck with your one baby.

A big mistake often made by beginners is to try and water by the clock or the calender, instead of by the needs of the plant.

A good way of overcoming this is to use the Finger Test. Poke your finger into the soil as far as it will go. If the tip of your finger feels cool and moist, don't water the plant. If dry, water it.

When I water my potted plants, I give them a thorough watering, making sure that the pot fills up with water, then flows steadily out through the drainage holes.

I've never known the sun or extremes of heat (from sun) to kill off a mint. I have known the sun to dry out the soil, however. As long as some of the roots underground are still alive, the plant will even survive this for a short time. If you're in the subtropics, you should have plenty of humidity to help your mint maintain a good moisture level. The soil in which mint grows should NEVER be allowed to dry out.

Honestly, some people will tell you ANYthing to get you to buy something from them! M for Mint = M for Moist.

Also, a leggy mint is a sign that it's not getting enough sunlight. The stems are literally reaching out for more light. Do yourself and the plant a favour by putting it outside if you can. Find a spot in dappled sunlight, or put it in a place where it will get morning sunlight (say, until lunchtime), then is protected from the afternoon sun. And the large pot really isn't an option - it's a necessity!

I've been told about the poke-the-soil method, but my problem is that I don't know what qualifies as dry enough to water. If it's ever so slightly damp, should I leave it alone? Would it be a good idea to add more perlite to the potting soil to aid drainage - what proportion of perlite to potting mix should I use? Also, if I leave potted plants outside, should I bring them in when it rains?

I think my best bet for partial shade is the East side of the house so that it's in the shade during the afternoon. I don't have any trees or bushes to put it under. The tile/concrete patio gets pretty hot when the sun is shining. Can you recommend a way to keep the pot and soil cool? This is the first time in my life that I've had a patio. Most people in Hong Kong live in high rises and don't even have balconies.

One more thing - does peppermint have different water/light requirements than spearmint? (I think it's peppermint, the plants aren't often labeled in English in the stores).

The heat won't hurt the plants. Several of mine are sitting on concrete pavers in the full sun (under my clothes-line, actually). Heat helps the plant to produce the essential oils which give them their particular perfume and taste. The soil will never get to anything like the same heat as the concrete, or even the air around it. A bit of mulch (straw, pet hair, dead leaves, whatever) on top of the soil will protect the top of the soil and also help to prevent water evaporation if you feel it's needed. You can always put the pots up on little feet, available at your garden centre, or just on a couple of bricks or blocks of wood of the same thickness, suitably spaced so that the pots are off the ground and air can circulate underneath - this will also help the drainage. I've never found it necessary, even though it's possible to fry an egg on the pavers here in summer!

Peppermint and spearmint, and most other mints have the same requirements. Check the plant labels for botanical names - Spearmint is Mentha spicata, and Peppermint is Mentha piperita. Spearmint is often called the Common or Garden mint (it's the one usually sold in the produce section of supermarkets) and has much paler and somewhat more rounded leaves than peppermint, and they are usually more dentated (more indentations around the rims of the leaves). Peppermint has quite dark green leaves and they are more pointed and thinner. The taste is a dead give-away - check after trying some spearmint and peppermint-flavoured toothpaste!

The Finger Test is a rule-of-thumb method. Judge it by practice and experience. It's quite OK to leave your mint out in the rain (they'll love it! when I'm well and able to do such things, I rush outside to put all my pots in the rain if they aren't already there - some I have under cover) and even to flood them to overflowing when hand-watering, as long as you've got good drainage, so that the excess water can get away quickly. The larger the pot, the more soil you have in it, and the less frequently you'll need to water. A good, thorough watering once or twice a week is far better for your plants than frequent mouthfuls anyway. Just make sure, when doing the Finger Test, that it never feels dry at finger tip. It should feel cool and moist at all times under the surface of the soil (ie around the roots). Terracotta pots will need a lot more water than plastic pots because the water evaporates through the pot. I have mainly plastic pots, but a couple of heavy concrete ones. I just rely on my trusty finger for all of them!

If you use a good quality potting mix, you don't need perlite or anything else added to it. Just never let it dry out, and when the plant gets potbound, and the level of the soil shrinks, just repot with fresh soil, or top up the level with more potting mix, or better still a mixture of potting mix plus compost (you should be able to buy compost in bags - get general purpose compost, not mushroom compost). This will replace the nutrients that leach out from pots. You can use just compost if you want. Proportions of soil/compost for pot topping up isn't important. Water it in and Bob's your uncle.

I left the mint outside for the last couple of days, and it was amazing how fast the soil dried out compared to when it was indoors. When it was indoors, it could go a week on a cup of water without showing any signs of moisture stress. Yesterday out on the patio it started to droop within 3 hours, so I drenched it thoroughly. By today the soil was already just slightly on the damp side. I think the newer leaves have started to get a bit bigger too. Interesting... Thanks for all your help!

Argh. My cuttings went moldy! I had them in a cup of perlite with a bag over the top. I took the bag off every day to air it out, but it went moldy anyway. Quite suddenly too. One night it was fine, next afternoon it had big black hairy spots everywhere. I'll have to start all over again. *sigh*

Maybe it's humid enough that I can do without the bag, or else I'll cut a bunch of holes into it.

At least I've got two slightly older cuttings that are doing fine, one in potting mix and the other in hydroculture pellets. I brought them back in the house because we've caught the tail end of Taiwan's typhoon. I think it's going to rain all week.

I don't know whether this helps of not... I've got some spearmint growing mostly in a shaded area and they're doing splendidly. *Shrugs* I mean, they don't like frost but they survive it.

Weather conditions have varied here... they've gone from draught to heavy rain and flooding, but these plants grew on their own from last year's seeds and haven't been affected by about anything...

Yes i lived out West and it was hot and dry, so i put down a plant giving by my sister, it was next to wooden fences and it got shade in the after noon and it did very good their it likes shade, it would get sun in the am and shade in pm, Blessing thank you