I received a pyracantha firethorn from Bonsai Boy in NY on 1/22/18 and it was great all through the week. After coming into the office yesterday (1/29/18) after the weekend, a number of the leaves are yellow as shown in the attached image.

Soil is moist and there was water in the drip tray all weekend. The bonsai is in a south facing window that gets at least 6 hours of full sun a day. Bonsai Boy support wasn't much help when I tried to contact them, so I'm hoping someone here can tell me.

They don't like to be inside in a dripping tray.
The dry air, the heating...

Their site claims that it will thrive indoors: www.bonsaiboy.com/catalog/firethorncare.html

SHStormont76 wrote:

Their site claims that it will thrive indoors: www.bonsaiboy.com/catalog/firethorncare.html

Nonsense. Apart from that, an office is about the worst place for plants. Also I don't think this qualifies as a bonsai.

Note that the instruction on the site is very generic, they simply copy the same instuction for about all plants that they say are indoor plants.

Seems this seller is quite popular. I have no idea why.

Pyracantha coccinea is the normal european firethorn. This plant is hardy like boots. You can (and I suspect should) keep them outside. Why they would recommend bringing them in is beyond me.

The yellowing of leaves could be a sign that the roots are too wet. And of course, in general, of too many changes in climate.

Do you know how it was kept at bonsaiboy?

PS: Bonsaiboy does not have a good name when it comes to their advice on bonsai care. Besides that, they sell lots of plants as bonsai that really are nothing but cuttings in a pot. For your next tree, look around a little. There is a lot of variation in what is being sold.

SHStormont76 wrote:

Their site claims that it will thrive indoorsl

Their site says a lot of nonsense.
Not a real bonsai nursery, it's all about selling as many plants as possible, unfortunately.

Thanks all. Unfortunately there was not much looking to be done on my part as I ended up receiving this as a gift.

I also read another site that mentioned the yellowing might be too much water in the soil and I was curious how wet the soil should be for this species? I do have a moisture meter (standard green one with a 1-10 scale) but I was curious if a generalization could be made to keep it in the "4-7 moist range, but no higher" or not.