You are right Beth in that the roots will dry up when the humidity drops but the presence of these roots means that a strong root system is developing below the surface of the potting mix.

Mike

Hi lightning

I agree whith mikedahms

common sense
If a plant is healthy at the bottom it should be healthy on the top.
aerial rootlets are by "too much humidity" in the terrarium. Sure they are very white

Beth I thought I would add this photo of a Hoya rooting onto the glass of my rooting aquarium.

Almost all Hoyas are epiphytes which means they grow attached to other plants like trees. The aerial roots serve two functions, anchoring the plant to a support and gathering moisture and nutrients. Hoyas can start their lives on the ground but they will eventually climb up high and the lower portion of the plant can die off. Because Hoya's seeds have a fluffy floss attached (like their family members the milkweeds)the seeds have a good chance of starting life off up in the trees or in other lofty places.

Mike

Quite a few of my Hoyas grow these aerial roots during last summer while they were outside. When I brought them inside for the winter, they died off a bit. Now that they are outside again, they are growing new ones.

The fact that I tend to water the whole plant, not just the pot probably encourages them also.

Here's a pic of one of mine from last summer. Some of the roots got about 6 inches long. At the time, I posted a question as well about them.

Hoyas are fascinating plants. All of your explanations make so much sense. Thanks Mike for that picture! What happened to that root when you took the plant out of the aquarium? The sight of aerial roots makes me wish I could give these hoyas something alive on which to climb... like a tree! That will never happen here in the frozen north :(

But it does make me wonder why humidity causes hoyas to put out aerial roots. For example, they aren't doing it because they have necessarily found something to climb. They produce the roots when it's humid. Any guesses why that would be?

In nature many Hoyas grow in humid habitats where for at least part of the year (or year around) it rains frequently. Aerial roots are able to grow in humid conditions and if you were able to provide perfect growing conditions you would notice that there would be many of these roots. This is the natural growth habit of these plants and the roots generally form at each node along the stem/vine. Many plants share this growth habit and one group that comes to mind is the climbing Aroids like Philodendron. Many people grow vining Philodendrons but unless these plants are grown in high humidity you might never see the extensive aerial root system that can be produced. The roots are just too delicate to be able to survive in dry air but they would normally be produced as new growth develops and by anchoring the growth in place the leaves can then develop and the plant will be secure and able to continue climbing or scrambling through other vegetation.

Here is a photo of roots that developed on my Hoya cleminsorianum cutting while it was in the rooting aquarium. These roots are in the process of drying up in the photo because I had placed the cutting out with the rest of my plants.

Mike

/mikedahms
Perfect explanation. I agree with you.
Most of them need high humidity.