I have had a Yucca for about a year and it was initially doing well, but now seems to be really struggling. I first noticed dropping leaves and some mildewy residue on the leaves (which I wiped off). Leaves then started going brown at the tips and then dying off. I've recently noticed that the new leaves growing out of the centre are coming through grey at the tips and with holes in (see image). The plant lives in a heated conservatory, so gets plenty of light.

Does anyone have any suggestions?

Does your container have drain holes?

Yes, it does

If the dying leaves are the lower, older ones, that is okay. It is also normal for tips to be drying off, especially if it is indoor and heater is running. But it has high tolerance for dry heat so it should be okay.

As for the middle part growth issues..seems to indicate watering, ventilation and lighting issues.

It is typically a high, direct light loving plant, so with insufficient light and its natural very slow growing pace, it is easy to cause those mildew issues. Make sure you do not mist this plant, just water the media directly as needed. Other than that, as long as it continues to grow new leaves and there is no soggy trunk, then just be patient and wait for better weather.
Indoor growing dynamics is different, the lesser light, lesser water.

I cannot see very well your media, I hope it is gritty and very well draining.

My Yuccas media looks like this..very gritty and well draining, just to give you an idea how I grow it. It is a must to make media well draining, since it gets rained on here during Winter to early Spring.






If your weather allows it later on, I would suggest move your plant outdoors. It truly grows better outdoors.

Hi Betsyboy888, to the site!

Your Spineless Yucca (Yucca gigantea) looks to have powdery mildew. What is the temperature range in your conservatory, do you have a fan in the room for adequate air circulation? Powdery mildew is usually a result of low light, cooler temperatures and poor air circulation and it can spread if ideal conditions are not met.

Thanks for the advice all. Temps where it is probably go from 13-18 centigrade (55-65 Fahrenheit) this time of year. It is fairly bright in there, but mid-winter here so not a huge amount of sunlight around!

Tarev - the growing medium is certainly not as gritty as yours. Largely still in what it came with, although I have added some cacti mix in. If and when it recovers I will look to improve it.

I have made the mistake of misting in the past - won't do that again. I suspect I have over-watered generally in the past. Is there anything I should do to treat the powdery mildew?
Other than that sounds like I just need to wait for some sunshine and warmth to return. Trunk is sound, so will keep my fingers crossed.

Hi & welcome! Agree, misting is more likely to cause damage than be appreciated by this kind of plant.

I'm not sure from the 2 pics, but I would probably be considering cutting off all of the foliage. Mildewed foliage probably can't go back to looking un-mildewed, and will just spread it to new foliage. For now, I would let the soil dry significantly until warmer conditions return.

How long until the nights aren't frosty anymore where you are? Yucca can take a light frost, no problem if it has been growing vigorously, but I probably wouldn't put an inside plant back out until that has passed. Unless there was some kind of more dire emergency.

Probably another month or so until the risk of frost has passed. Cut off all the foliage - that sounds quite drastic! Would I be better to wait for things to warm up first?

It does sound drastic, but is a pretty common thing to do, usually done to keep plants from getting too tall for their surroundings. Waiting until it can go outside sounds like a fine plan.

Here is one 6 mos after all of the limbs were cut:

After 11 months:

Bestyboy888 said: Probably another month or so until the risk of frost has passed. Cut off all the foliage - that sounds quite drastic! Would I be better to wait for things to warm up first?

Yes, best to wait patiently till your overnight temps has reached a stable 50F and higher. Yucca is such a slow growing plant anyways, so it can wait. In the meantime, just trim off any dried out leaves, or if leaf tips looks pokey, cut the tips off, no misting. If you have a fan let the air bounce from the ceiling so it simulates ventilation around it, do it after you water the plant.

Depending on outdoor conditions, it does take awhile for the plant to regrow new leaves and new arms. There was a time my Yucca mommy plant has grown too tall and is dangerously at eye poking level, so I waited for late Spring/early summer to do a hard prune. What I noticed is that, if roots were not disturbed, it has a faster come back, maybe in three months or so, you will see new leaves sprouting. But if you chopped it down and attempt to replant stem cuttings, it can take a year or more. But as long as it is not mushy, it will come back, very slowly.
There was a bare stem cutting I was ready to yank off the container since it was like a year already, to my surprise oh, it is finally breaking out...so that was how slow it goes, a real good lesson for me to exercise patience.