I just noticed Planto left comments. Planto, sorry if I repeated anything you said. Blabberboca. Your Dracaena looks a lot taller on your link. Are roots growing out of drainage holes? If so, your marginata definately needs a larger container. Before, I forget. You said you watered straight from the tap. Is it possible to fill a container w/water and let it sit overnight before watering?? Is soil crumbly after you water?? How often do you water, and do you water thoroughly so rootball is saturated? Sips don't do the job. Ah, you have a garden window..Lucky you! :) Yes, I'm certain a south, 'semi-enclosed area' gets hot in summer. Is it possible to move your marginata in the background, or another room? During winter, your garden window would be a great place to for your marginata and other plants. Don't fear repotting. :) Select a larger container, (5-6")add a little soil on the bottom of new pot. Remove plant carefully from old pot, center in new pot, then add fresh soil around the rootball and top.. Once you repot, you'll soon be an expert...lol.

What kind of filtered water? If I go only by odds and reasoning, the first thing that comes to mind is that you are over-nurturing - which translates to over-watering, even though you say this is not an issue. Salt accumulation in the soil (from fertilizers and irrigation water) is another strong possibility, as is natural abscission (losing leaves) due to a reduction in already low light levels. The moisture meter doesn't work. It measures electrical conductivity - not actual moisture content, so it's actually closer to reliable as an indicator of fertility levels than of moisture levels, although it's really not a reliable tool for measuring either. Test your plants by checking the soil at the drain hole & only water when it feels dry there. Al

"This tree was planted about 2-3 months ago, with ammended soil in full sun." Generally, it's not good to amend the backfill soil when planting trees or shrubs. Amendments frequently cause drainage issues and root development problems. "I'm not sure what type of fertilizer it has been given, but nothing within the past week." Trees and shrubs don't often need to be fertilized. Improper fertilization can cause serious problems or death of the tree. Have you had a soil test that indicated a need for additional nutrients? When you say it hasn't had any fertilizer in at least a week, it sounds like it may have been receiving mega-doses of something prior to a week ago. Surely you aren't fertilizing the poor thing once a week! "It was watered for between 30 min to 1 hour every other day and looked fine until a few days ago." Wow, that sounds like a lot of water! Have you been checking soil moisture in between waterings? I don't know what kind of soil you have or how much water you have been supplying, but your description definitely raises a red flag for way way too much water. Are you sure you are not drowning the tree? Trees can die from too much water as easily as from too little. With the information given, it's impossible to say for sure what's happening with your tree, but it sounds like overwatering may be a likely suspect. Other planting issues may also have contributed to the problem. Details of how the tree was planted (planting depth, condition of roots at planting, how the roots were conditioned for planting, type of native soil, relative amount and type of backfill amendment, etc, etc) might lead to further insight. You may also want to carefully read the article linked below, for future reference and for possible help in further diagnosis. Here is a link that might be useful: Planting a Tree or Shrub

I think the experts are going to want to know what species of palm you're talking about. Can you post some pics? You say "several of the leaves are turning yellow"... are they the oldest leaves? That would be natural. Any idea of how established the palms are? Were they recently transplanted by the seller of the home for curb appeal? If so, its possible that you have too many fronds/leaves for a newly transplanted palm. You say you had them "trimmed"... if that meant removing the oldest leaves, that is the right thing to do. But recently transplanted palms should have only two or three newest leaves emerging. All others should be cut off. By the way, the "needle palm" makes a wonderful under-story shrub palm and is completely dependable. It grows as a clump and only gets to be about 10 feet tall. There are both blue and green varieties available.