Dendrobium spectabile roots turning brown

[etcherkate]

In June I adopted a cat who is absolutely determined to eat every plant in the house, with the exception of the catnip I grew especially for him. In the last few months, I've moved most of my plants onto a shelf wrapped with three sides with a shower curtain, with chicken wire secured to the front with bungee cords. LED lights are suspended about 6 inches above the tops of the plants, which are mostly orchids with one tray of herb seedlings.

The orchids seem to be adjusting well to their new conditions--I was able to keep them alive near the windows, but with the exception of a few phals, none were blooming or growing vigorously. Under the LED lights, and with the increased humidity provided by the shower curtain enclosure, most of the plants have been exploding with new roots and leaves. Three out of six phals are growing spikes; one phal is growing two spikes at the same time, which is a first for me. I'm hopeful that this will be a good year for the other genera, none of which have ever rebloomed since bringing them home.

This week I noticed that my Dendrobium spectabile has very suddenly developed brown roots. It seems to have happened shortly after watering and fertilizing. The brown started just above the green root tips and is spreading across the entire root. The roots beneath the bark look healthy. I wonder if this is fertilizer burn? I water this plant about every 7 days, and fertilize afterwards with a 20-10-20 liquid mix, approximately three out of every four weeks. I poured the fertilizer directly on the roots, forgetting that this has damaged phal roots in the past--though the damage to the phal roots seemed to happen more gradually and looked very different.

Any insight into my dendrobium problem is greatly appreciated, as well as general advice on my conditions. Most of the plants seem to be happy with the new lights and increased humidity, though I do have a problem with tiny gnats, and several phals immediatly lost multiple leaves after they were moved--not just the leaf at the very bottom of the plant. Thanks in advance!

[estación seca]

What fertilizer dilution did you use? Den. spectabile needs to not get dry while making active growth. Have you let those roots dry out for long?

[etcherkate]

Originally Posted by estación seca

What fertilizer dilution did you use? Den. spectabile needs to not get dry while making active growth. Have you let those roots dry out for long?

Hi Estacion! I'm using 1/2 teaspoon of fertilizer diluted in 1/2 gallon of water. I water this plant about every seven days, and the roots outside the media probably get pretty dry inbetween waterings. I always water before fertilizing, but this week I was impatient and only waited ten minutes or so before fertilizing.

[estación seca]

That's a very large amount of fertilizer for an orchid. It's more appropriate for other kinds of plants. Orchids don't need much fertilizer.

Using Ray's fertilizer calculator
Nitrogen Management Calculator - First Rays LLC
and playing with numbers, you are giving something like 320 parts per million (ppm) nitrogen almost every week. Many people suggest 100-125 ppm N if used weekly, and many people have great success with half or a quarter of this amount.

I suspect the problem may also be roots getting too dry between waterings. This group of Dendrobiums does much better if the roots don't dry out while growing. A small-particle medium may not have enough air to the roots if kept wet like this, but then there is the time problem - most people can't water plants in large chunks of medium every 1-2 days.

By the way, watering before fertilizing has not been recommended for decades. This practice saturates the roots with plain water and prevents them from taking up the fertilizer. Agronomy schools for decades have been teaching to fertilize dry roots.

[Dollythehun]

My roots looked similar. The plant is doing well though. Don't fertilize it during the winter or it'll just keep growing and not bloom. Water, give it bright light, and it'll quickly fill the pot with roots.

[etcherkate]

All of this information on fertilizing orchids is great to know--thank you! I've often heard the advice to fertilize "weakly, weekly" but assumed that the dilution instructions on the fertilizer container were weak enough, since the product claims to be formulated specifically for orchids.

The idea of giving this plant a winter rest from fertilizer is another helpful thing to consider. I've been told that this plant won't be near blooming size for a couple more years; I wonder if it still needs a winter rest?

[Dollythehun]

If you type that into the search engine, you will find a useful thread. The Orchid Whisperer and I had a conversation about mine. It's probably three years in my care. They grow roots like mad and if you keep feeding them, they just get taller and grow more roots. Mine now has bud nubs forming.

Dendrobium spectabile - the alien orchid

[estación seca]

If you go to the First Rays Web site via the link to the fertilizer calculator I gave, there is an entire section on fertilizer and its use. You can learn a lot there.

Den. spectabile grows to become a very large plant. As Dollythehun wrote, it grows fast when it's happy.

[leslie123]

I don't know about your Den. spectabile, but I can recommend Synergy Fooey! spray to keep your cat out of your plants. I have a very insistent cat - I think she considers Bitter Apple a condiment. I've tried another 3-4 other sprays, no use. But Fooey! (it has the exclamation point) does the trick. It also keeps deer from eating my roses. It is the most awful stuff I've ever tasted -- I spray it with plastic bags around my hands, and only when there's no wind, because the airborne essence tastes awful and it takes hours to come off my fingers. But it taught the cat to leave my plants alone. At least, the plants I dared to spray. (I have to touch them, too.)