Brown Thumb, Redux

November 1, 2007 11:05 AM

I killed my plants... again... what did I do wrong this time?

I decided to try to grow some herbs again. The parsley I planted in my window box has developed thin, white patches all over the leaves. These patches also have black spots in them, but I'm not sure which showed up first. Also, about the same time the white spots appeared, my apartment became infested with fruit flies. I think the flies came from either the plants or the potting soil I used.

So, the question is - what happened to my parsley, and will it be transmitted to my other herbs? Is there anything I can do to save the plant? Is is still safe to use?

posted by backseatpilot to home & garden (9 comments total)

The important thing with herbs is mixing the soil well and not packing it into the pot tightly. Water as directed with sunlight access. The fruit flies could be because of standing water in the pot plate or the soil is saturated with old water (in which case you might want to swap out the soil for new soil).

Not a plant expert, but eating herbs with unidentified spots on them is not a good idea. They might even be the fruit flies' egg sacks. You could try washing it off the plant and see if it's within the leaf or just on the surface to save it, but wait awhile before eating to see if the spots come back.

Happy planting!
posted by blueorchids at 11:15 AM on November 1, 2007

More info for us please. What is the exposure of the window? N, S, E or W? Shaded by trees? Is the window box inside or out? What kind of potting soil did you use? How big is the box and how many plants do you have in it Are the other herbs doing OK?

Fruit flies like very moist places to breed (hence fruit). If they are coming from your herb box, then you are most certainly watering way too often.

I wouldn't use the parsley. It's not unsafe, I just prefer not to ingest anything I grow that wasn't thriving. Parsley is usually only affected by fungi. If this is the case (can't tell without pics, and even then..), it might be another indicator of overwatering.
posted by a_green_man at 11:21 AM on November 1, 2007

I agree that it sounds like a fungal infection. Avoid overwatering and watering the foilage too much.
posted by empyrean at 11:26 AM on November 1, 2007

Well, the window box is sitting inside a southeast-facing window, not shaded by trees. I think I used Scotts top soil, but I threw the empty bag out awhile go. The box is the width of a standard sized window, so... 16 inches? There's a dying pea plant (it was sort of DOA anyway, so I don't want to include it in the diagnostic) and a basil plant which is doing quite well, in addition to the ailing parsley.

I've been watering once every three days or so... enough to get the soil visibly moist on top. The white patches on the parsley actually look like there's cellulose missing from the leaf - it's almost translucent at those spots.

Thanks for the help!
posted by backseatpilot at 11:52 AM on November 1, 2007

From your last comment, it almost sounds more like something is eating your leaves. Pictures would definitely help. Are you checking that the soil is dry two or three inches down before watering? If not, you may be watering too often, in which case fungus is a possible problem. It's really hard to tell what's going on from your description. The flies may be living in your potting soil- they like to lay their eggs in rotting fruit or fungal bodies most often though- however, if you're keeping your soil too moist they may move in there. I don't consider them an issue for plants, but they suck to have in the house. You can mulch indoor potted plants just like outdoor plants, and that will help. Use micro bark- it's looks nice, and is coarse enough to break down slowly enough to not tie up nitrogen (usually).
posted by oneirodynia at 12:04 PM on November 1, 2007

I would bet that you have a whitefly infestation. Whiteflies are similar to fruit flies, however they are a little more opaque in color.

They are very, very hard to get rid of, and they will quickly infest other plants in your home. Your best bet is to just through out the afflicted plant. Once the plant is gone and there is nothing more for them to feed on, the ones flying around your house will die.

Whiteflies secret honeydew, like aphids. The black spots on your plant could potentially be mold growing on secreted honeydew.

It seems like everytime I have a whitefly infestation, they are already present on the plant when I bring it home. So, it's not something that you did. You probably already had little hitchhikers when you brought the plant home.

Also, be sure that you are using potting soil, not plain ol' topsoil. Potting soil is lighter.

Good luck with your next plant ... sorry about this one.
posted by Ostara at 12:27 PM on November 1, 2007

Agreed... Letting the soil dry out a bit between watering is important to prevent some of the things you've mentioned here. Watering every three days might not let that happen. Plants grown indoors do not dry out as quickly as plants grown outside. Overwatering smothers roots, deprives them of air circulation, and therefore can stress the plant, making it more susceptible to other problems. As others have said, constant moisture can allow fungal disease to grow and flourish too.

Also, I wonder if you have fungus gnats instead of fruit flies? They look similar, but the gnats lay eggs in the moist soil, hatch, and repeat, whether you have fruit around or not, and they swarm like fruit flies when you disturb the plant in any way. These fungus gnats are very common too and thrive in a moist environment. And you're probably right: there might also have been eggs in your potting soil, since not all potting soil is guaranteed to be sterile, and since most brands have a lot of peat moss in them that allow the mix to hold more water.

To get rid of the gnats, the soil needs to dry out and not be watered for awhile. You could put your window box near a fan to accelerate this. I've also heard that putting a layer of sand on the surface of the soil can sometimes prevent gnats or trick them into believing the soil is too dry for them, since sand doesn't hold onto water very well. (As for the ones already swarming your house, hanging sticky paper might help catch them.) You can always just throw it out too.

If you have a whitefly infestation, you will be able to see their tiny whitish eggs on the underside of the leaves and down the stems. They don't hang out in the soil, so it should be pretty easy to tell whether it's whitefly or fungus gnats. From how you described the tiny cellulose-like spots on the leaves, they don't sound like the whitefly spots I've seen, but you can judge that best.

So if your goal is to have edible herbs, I too wouldn't eat the parsley with the unknown spots, so you might decide that it would be easiest to start over with new potting soil and new plants (in a container with drainage holes, if you don't have that already). Good luck - it's frustrating to enjoy plants but have challenges in growing them. I've known many people who were convinced that they had brown thumbs until they laid off watering so much - indoor plants especially can handle being drier than you think, and I was always told that you can kill most plants faster by overwatering them then by underwatering them. I hope that helps!
posted by onoclea at 12:49 PM on November 1, 2007

I think I used Scotts top soil

Top soil should not be used when growing potted herbs. A good potting mix should be used instead. You can even make your own.
posted by LoriFLA at 12:50 PM on November 1, 2007

Yeah, I would transplant into potting mix (I use a brand I can't think of in a bright yellow bag, marked specifically for flowers and vegetables) as soon as possible. It usually has vermiculite or similar absorption media in it that will help a watering last longer. I also use a granular slow-release tomato & vegetable fertilizer on my herbs, and they really seem to dig it.

Most herbs are not fussy - they want to dry out a little. Be a little meaner to them.
posted by Lyn Never at 5:37 PM on November 1, 2007