s/h & fungus gnats & old roots --> how old is old?

[SarinahL]

So I wanted to try s/h for some of my plants, but this immediately raised some questions:

- old roots, how old is old? I mean, I have a dendrobium keiki that I would try for this experiment. The roots are all around 2 inches long, with active tips. The keiki is around 2 months old. Would these roots still be able to adapt, or would these die?

- is this advisable for seedlings in general? The reason I ask this brings me to the third question:

- I have a constant fungus gnat problem. They especially love the seedling mini-greenhouses, they seem to leave the rest alone. They are in bark and sphag now. They already started to do some serious damage on the new and tender roots and I'm thinking, if I put these in s/h, would this still attract fungus gnats? And if no, would s/h be a good idea in any case for the youngsters?

Thanks!

[Ron]

Originally Posted by SarinahL

So I wanted to try s/h for some of my plants, but this immediately raised some questions:

- old roots, how old is old? I mean, I have a dendrobium keiki that I would try for this experiment. The roots are all around 2 inches long, with active tips. The keiki is around 2 months old. Would these roots still be able to adapt, or would these die?

The kikis roots being 2 inches long and in active growth would be a great time to pot on into a pot.
Should bolt away with good growth.


- is this advisable for seedlings in general? The reason I ask this brings me to the third question:

- I have a constant fungus gnat problem.

Gnats love a sour potting mix, mix a spoonful of common garden lime in a gallon of water and stir well and pour enough over the potting mix so it flushes right through the mix.
That easy.
as for the fungal problems, look at improving the air flow around the plants of put in a small fan.


a They especially love the seedling mini-greenhouses, they seem to leave the rest alone. They are in bark and sphag now. They already started to do some serious damage on the new and tender roots and I'm thinking, if I put these in s/h, would this still attract fungus gnats? And if no, would s/h be a good idea in any case for the youngsters?

Thanks!

Best of luck

[SarinahL]

Thanks Ron!
I don't have a fungal problem though, I do have fungus gnats. Or isn't that what they're called?
And is s/h also good for seedlings? I mean, I've read everywhere that only the roots that have been grown newly in s/h are suited to that environment. They keiki's roots always have been up in the air, and seedlings' have been in bark and spagh. I wouldn't want to kill the few roots they have..

[Ray]

If you have a fungus gnat problem, you HAVE fungus.

The term "fungus gnat" applies to a number of species of insects. Fungus gnat adults are a mostly a nuisance, but the larvae can damage healthy roots, stunting or killing young plants even where there is no fungal food source. Prolonged infestations may cause stunted, off-colored plants or foliage. Damage may actually be more severe to young plants when the potting media is fresh, as there is less fungus available as a food source. Fungus gnat larvae may also aid in the introduction and spread of plant diseases such as Pythium, Verticillium, Cylindrocladium, Scelerotinia and Theila-viopsis.

The best time to repot is just when the new roots are emerging, but you'll probably be OK at 2".

I think you may be missing the point with semi-hydroponics: pretty much any plant at any stage can do well in that type of culture, assuming the rest of your conditions, coupled with the S/H root environment, are right for the plant.

[SarinahL]

Originally Posted by Ray

If you have a fungus gnat problem, you HAVE fungus.

I remember reading somewhere that that is not always necessary. That it could start with one infected plant (with fungus), but that they wouldn't be too particularly picky in their breeding ground choices with the surrounding plants. It would be weird too, because all the medium used dries out fairly quickly (I need to water every 2-3 days) and is brand new. But that doesn't say much, though

The term "fungus gnat" applies to a number of species of insects.

A number of species? What we have here in the Netherlands is just the one specie, I believe

Fungus gnat adults are a mostly a nuisance, but the larvae can damage healthy roots, stunting or killing young plants even where there is no fungal food source. Prolonged infestations may cause stunted, off-colored plants or foliage. Damage may actually be more severe to young plants when the potting media is fresh, as there is less fungus available as a food source. Fungus gnat larvae may also aid in the introduction and spread of plant diseases such as Pythium, Verticillium, Cylindrocladium, Scelerotinia and Theila-viopsis.

The best time to repot is just when the new roots are emerging, but you'll probably be OK at 2".

I think you may be missing the point with semi-hydroponics: pretty much any plant at any stage can do well in that type of culture, assuming the rest of your conditions, coupled with the S/H root environment, are right for the plant.

Thanks, thats reassuring. I've read so many forum topics with various posts on not to try this on seedlings.

Okay so, but would this decrease the chance of gnats in the medium? I'm going to also try the lime idea, though, thats a new one for me!

[Brooke]

If you have a fungus gnat problem you probably have a plant in your house with a peat based potting mix. Fungus gnats reproduce inside and outside by burrowing into your potting mix and the ground you walk on. They eat decaying matter and not the "fungus" associated with orchids.

To eliminate them inside you can soak a mosquito dunk in a gallon of water and water your plants and it will kill the larvae. You can also purchase a prepared product to kill the larvae but it is expensive as compared to a dunk.

Insert a raw potato slice into the potting mix for 12 hours and you can harvest the larvae. The larvae are white and about the size of a grain of rice.

The adults are attracted to the color yellow so the sticky traps or fly paper attract them.

You can use a gritty substance on the top of the potting mix and the adults won't reenter to lay their eggs. I used a granite product used as a chicken/turkey feed.

If you water from the bottom so the top stays dry the adult gnats will not reenter the mix and it won't be moist enough to reenter.

If you switch to Coir peat, fungus gnats will not lay eggs in it. They also will not lay eggs in bark, LECA or sphag.

If you want to continue using a peat based mix you can sterilize the mix in the oven or the microwave - WARNING - it stinks but the heat kills the eggs. Freezing the mix will not kill them because much of the peat comes from peat bogs in the frozen north - think Canada or Wisconsin.

If you google fungus gnats you will learn their life cycle and how to eliminate them. The adults are very short lived and you can eliminate them if they cannot reenter and lay their eggs.

Brooke

[Ray]

Originally Posted by SarinahL

Okay so, but would this decrease the chance of gnats in the medium? I'm going to also try the lime idea, though, thats a new one for me!

If you totally eliminate organic matter in the potting medium, you will eventually reduce the likelihood of having fungus gnats. However, as Brooke pointed out, they may not be originating in your orchids, so may still see them from time to time.

Also, if the orchids are your only plants, it is possible that larvae can be within the root system itself, especially in cases of heavy infestation, where they have "cleaned out" the fungus supply already.

I will have to disagree with Brooke on the "won't lay eggs in bark" comment. Fresh bark, certainly not, but as it ages and decomposes, bark too, can provide the perfect moist environment for fungal growth, and the adults will, indeed, lay their eggs in it.

So I guess the "bottom line" (in my book, anyway) is:

1) Treat all plants with an insecticide to kill the population, then
2) Move them to S/H to lessen the likelihood of their recurrence.

[Ray]

What "lime thing"? You DO NOT want to use horticultural lime on your orchids, as that can increase the pH to dangerous levels. Brooke mentioned granite, which is not nearly so soluble.

[SarinahL]

Uhm, Ray, this was Ron's suggestion. To use common garden lime...
So better not then...

[Ray]

Oh, Right. I missed it.

His recommendation might not be SO bad in small doses, but I think it's treating the symptom, not the cause.

[Ron]

Originally Posted by Ray

What "lime thing"? You DO NOT want to use horticultural lime on your orchids, as that can increase the pH to dangerous levels. Brooke mentioned granite, which is not nearly so soluble.

I and thousands of Orchid growers in Australia use it on our orchids every year.
On our Natives, Cymbidiums etc.
Without using it and using chemical fertilizer the PH drop far to low for healthy growth often around 4.5 if left untreated for a long period of time.
For example I put about about 2 spoonfulls of garden lime powder on my Cymbidiums each spring as part of my regular fertilizer program. then water it all in,
works perfectly, even after six months PH is not much lower than 6.
a week ater using it reading are no higher than 6.5.

[Ray]

Hey Ron.

When I first read the "I'll do the lime thing", I had just read the recommendation for granite grit on the surface, and mistakenly assumed Sarinah was planning to top dress with lime!

When I went back and actually READ your post, I wasn't so shocked!