The soil does not need to stay moist. Let it dry out between waterings. Lemon balm can tolerate the driest locations I have. I think you are keeping it far to wet - the rotted leaves you pulled out agree!

You can vigorously trim a healthy and happy lemon balm every few weeks. After 2 months, you should have lots of new growth and barely see the clip you gave it.

Lemon balm does prefer full sun. Can you move the pot to get it more sunlight?

FataMorgana

In your zone, now is the time that lemon balm should be growing. I agree that in a pot it should not be overwatered. Cut back on the water and watch for new leaves. If they still have burned tips, it is possible you have a salt buildup in the soil. In that case, repot and divide the clump.

Here is a link that might be useful: The Herb 'n Cowgirl

Yeah someone told me the burned tips were Rust disease. I don't quite buy that yet. I also read that Lemon Balm likes to have some shade that is why I moved it. Originally I had it in a more sunnier location. Guess I will move it back and cut back on water.

I have had these burned tips problem for awhile. Pretty much ever since I transplanted it to the pot. I have never had a healthy leaf on this plant.

Try a different pot or different soil, if you question that.

Letting the herb be on the drier side will make the leaves have a stronger flavor. One of the things we are asked about here (usually in the spring) is weak tasting herbs. Usually it comes down to waterlogged/over watered plants.

If you suspect disease and want advice, you'd have to post pictures of the plant.

FataMorgana

Lemon Balm is a member of the mint family, and it likes plenty of room to move. Such a small pot will not suit it at all - it will be tightly pot-bound. Either get a much larger pot and repot with new soil, or divide the plant into as many separate plants as you like, and repot each section in a separate pot.

A severely pot-bound plant cannot obtain enough water or nutrients from the soil - in fact I'm prepared to bet that there isn't a whole lot of soil left in that small pot! Try drinking through a bent straw to see what I mean. So when repotting sections, select the straightest roots you can find for the healthiest plant - roots which are curled or crushed can be chopped off - they won't do the plant any good, anyway, and once curled will never straighten out.

In a hot climate, lemon balm (and other mints) do best in filtered sunlight, or in partial shade during the hottest part of the day. They also like plenty of water (people in my part of the world often grow mint in a pot under a constantly slowly dripping tap), and I NEVER allow potting mix to dry out - it becomes water repellent.

Rust in mints can be fixed by removing the plant from the pot, giving the pot a good scrub with soapy water into which you have put a glug of household bleach. While it dries, wash off as much of the dirt around the root ball as you can, and swish the whole plant in the bleached water left from the pot-cleaning. Give the plant a thorough, heavy pruning to remove any remaining spores. Another method is to cut the mint (or in this case the lemon balm) right back almost to soil level, cover with a small amount of straw, and set the straw alight. (You won't do this if the pot is plastic, will you?) The fire/heat kills the spores which are on the plant and on the surface of the soil. The roots are not affected, so the plant will quickly bounce back.

One little trick I have found helpful with mints is this: stick a long rusty nail (of the building kind) into the soil and leave it there. Mints respond well to iron, but don't overdo it.

The Lemon Balm has not filled out the pot. The roots may be filled out on the bottom though. I do remember it having a big root system and also know mints have pretty good sized rootballs.

I have some chocolate mint in a much smaller pot and it does pretty good. In fact it does the best out of all my mints. I will post a pic of the Lemon Balm to see if it is indeed Rust disease I am dealing with. I can't really provide a bigger pot for it so I may have to divide the plant. Thanks