Since neem oil works as a contact insecticide with soft bodied insects like aphids, the results should be immediate. Most sources do suggest repeat applications to catch any egg hatch or missed adults in a week or so.

With contact insecticides, you need to spray all surfaces of the plant very carefully. Additionally, spraying the plants down thoroughly with water at the kitchen sink should accomplish similar results with aphids.....just swoosh them away!

yup, water spray. follow with soap spray, works better than neem. May need to repeat a few times

You don't need the soap - which some seem to think is a cure-all for anything. Since we are discussing houseplants and generally something easily transportable, the kitchen sink and plain water will work just as well. Or use the shower for larger items. And it will create an area of increased humidity (at least temporarily) that will discourage spider mites, who prefer their habitat warm and dry. And plain old water will never cause phytotoxicity.

And since we are talking about houseplants, they are unlikely to experience the conditions that encourage phytotoxicity - strong sunlight and high heat - although there are some houseplants that are overly sensitive to both soap or oil sprays: jade plants (Crassula sps), euphorbias, most succulents, ferns, palms, ivy, begonias and gardenias. All well-documented and easily researched, despite flip and feeble attempts at humor with this topic.

As always, read the label carefully, apply only as directed and if you think your plant may be sensitive, test a couple of leaves before any wholesale spraying is done.

"some posters just aren't really qualified in biochemistry. Chemistry. Or, apparently, evaluating much phytotoxicity, either. :-)"

Ain't that the truth!! And some display minimal horticultural knowledge, preferring to fly only by the seat of their pants. Re: the magnolia - since the plant in question was suffering from physiological damage, spraying with soap is uncalled for and unnecessary so phytotoxicity doesn't even enter the equation! Talk about blowing things out of proportion! LOL!!

"Most toxic people just love to stir garbage, drag you down to their level, and try to make you feel as awful as they spend their entire lives feeling."

Again, ain't that the truth! :-) Apparently some have such fragile egos and are SO sensitive about any possible criticism or a differing, fact-based opinion, that they can only counter with personal insults. Unfortunately, it's just a cross the rest of us have to bear. Odd that they also have great difficulty determining who is laughing at whom!

You're preaching to the choir. :-) Do you find you use 1 tsp in 1 gallon water equivalent?

Indoors, I confess to using an atomizer--4 oz, in which I use about 4 drops of soap. All things considered--yes, yes, I'm an untutored boor and fly by the seat of my pants--it's a fairly weak solution but seems to do the trick on most things.

I haven't had issues on anything I've personally tried it on (and I grow some whacky, whacky stuff, including succulents, ferns, palms, and ivies both indoors and out) in amounts up to 1 tsp in 1 gallon (a 0.13% solution of a sodium surfactant, not a soap).

I tend not to use soaps (even though I'm a soap maker) because the soap I make is sodium-based and, hence, a solid. I haven't bought a soap since...er...what decade is this? COVID-19 should fear me; I knocked together a high-stearate soap with a pH of nearly 10.5 and super-suds that I doubt it can survive for one second, much less the entire chorus of Spears' "Hit Me Baby, One More Time." ... Don't judge me. :-)

Similarly, I'm unafraid to pull out the Bayer when the trick isn't, as they say, well-turned. That's got to be an option, but I will say I'm not real happy using it indoors just because I tend to be extremely conservative with exposure to such things (I already spend time with cadmium, cobalt, and titanium on my hands).

I'd recommend that OP spray it outside if the temps are appropriate, or in the garage if that's above freezing, and bring the plant in once the spray settles--and rinse the plant before letting it hang around and evaporate. Yes, yes, it's not supposed to do that. A lot of things aren't supposed to happen, but do. It's why I even clean my cuticles with an old toothbrush before eating.

Let's not even discuss neem. There's been...a major issue when I pointed out it's an abortifacient and can cause spontaneous loss of pregnancy early on, or in cases where the pregnancy is not going well. Houzz moderators had to intervene. One guess who.

It's not a major issue later in pregnancy, and won't be at all an issue for most people (the dose being low)...but it's unwise to take chances, particularly in the case of difficult pregnancies, or early in any given pregnancy. File it under, "Better Safe Than Sorry," along with exposing yourself to anything made from elderberries, catching rubella, and playing tackle football when trying to become pregnant.

Some cats also show adverse reactions to neem, up to and including death. This is, fortunately, quite rare. But it's wise to keep neem away from both toddlers and cats.

So I think the issue here at least where I live in southern California is the aphid problem is really fierce. There seem to be an infinite number of them.

I did start outside with water - using the hose to spray them off plants they had infested. The problem here is that it is hard to do this with complete thoroughness because they can literally cover every leaf on a plant! I have them on my arugula outside, and they literally cover every leaf! The arugula is rather fragile so in spraying them I can damage the plant, as it takes a rather powerful spray to dislodge them. Then within one or two days they are back, covering every leaf as usual, and I spray again and the whole process starts over. At this point I've actually given up on the arugula, because despite my best efforts to get them off the plant, I think they have sucked so much life out of it that the leaves are no longer in a condition where they are edible.

I also sometimes try removing the aphids with tape on my thumb - this also works, but when their numbers are large, it gets tedious.

I purchased the neem hoping to find a more permanent solution that was also organic, and I had read some success stories with it. I have not yet read about any other organic solution that people reported success with.

But now, a few days later, after daily spraying my indoor plants with the neem/water/bonner's soap spray I mixed up -- sometimes two or three times! -- what I can say is that I have not yet noticed ANY effect!

The aphid are happily ignoring the neem and going about their business.

The thing about my indoor plants is that even if I can get all the aphids off the green, there are still flying aphids swarming around them at all times. If I tap the side of a container, the flying aphids get excited and suddenly come up in a cloud and start flying around. And just like the outdoor plants when I go back the next day, there is a new population on the leaves. They have now started to attach themselves to my dill, which I wasn't expecting - I guess they will attach themselves to anything! They are particularly hard to see on the dill, and also more difficult to remove without damaging the more fragile parts of the dill.

Neem does work, but...unlike posted above, it's not instantaneous. Give it a little time to work. I didn't say anything because, frankly, pointing out that poster is incorrect is an unpleasant experience in and of itself, worse than aphids.

It tends to take some time, but the numbers should decrease over a week or three. Neem will interfere with their ability to reproduce. And I really wouldn't quibble with adding soap in at this time already if you're having that severe a problem with them!

(No, phytotoxicity won't be a problem on most plants; use 1 tsp in 1 gallon water, spray the plant, let it sit for a minute or two, then rinse it off. That's not enough to cause a problem and removed too quickly to damage most plants--and would do far less damage than the aphids are doing anyway).

If you really do notice these not working then it's time to pull out some larger guns--insecticides safe for edible plants.

But it's likely they'll work fine and you won't have to.

I recently got a gallon pump sprayer to make life easier and love it. I have used dish soap (detergent) in the past with better results than I am having with real soap-I got ivory bar soap that appears to have the true soap ingredients and used about one tbsp and then two and still got plenty of aphids survive the dousing. I don't wash them afterwards either unless I am eating any part of it. I may have to increase the strength further or use Bayer.
I am not too concerned with the chemical. I spent years he in chemistry labs, including for PhD and in the industry at large scale. Our research labs had people running chromatography columns with Benzene. :)
As to neem, in our villages in India, people still use fresh twigs off the tree as disposable tooth brushes. That makes me think the fears of neem toxicity are greatly exaggerated. After all, people have centuries of experience using them and would know if it hurts. Just saying off the top of my head without any research..
Manic, I feel for you. I would suggest resorting to Bayer 3 in 1 based on my experience. I have even tried ladybird beetles, released small batches indoors and tried to make them eat the aphids. I had some success in that some even laid eggs which hatched into little larvae :) . Perhaps, you can try those. They are pretty cheap and considering you have a significant population of aphids, the ladybirds might just make it their habitat. I understand that lace wings are a more effective option but can't speak from experience on those.

Oh, honestly.....let's get over this childishness!! Previous poster should really get his facts straight before unnecessarily chiding others - and unnecessarily rudely - as making incorrect statements when his are the inaccurate ones.

Neem is a horticultural oil. Horticultural oils are contact insecticides when used to control soft-bodied or plant sucking insects (like aphids), their eggs and larvae. Contact insecticides kill by smothering so the insects must be present at spraying, coated with the oil and yes, the effect is pretty much instantaneous (within minutes), except for those that might be missed by the spray. Doesn't take a rocket scientist to research this and should be confirmed by the product label.

Neem also has an ability to kill other insect types by interfering with their digestive or reproductive processes but these are not soft-bodied, plant sucking insects.

manic_gardener, I would also suspect you have something in addition to aphids bothering your houseplants. Aphids rarely ever fly. Only females and then inconsistently - only late in the growing season or when food sources run low. And never to the extent that they would be present in a "cloud". That could be something like white flies or fungus gnats. If you can post of photo of your plants with the insects present, that could help to confirm an ID.

"dish soap (detergent) in the past with better results than I am having with real soap-I got ivory bar soap that appears to have the true soap ingredients and used about one tbsp and then two and still got plenty of aphids survive the dousing. I don't wash them afterwards either unless I am eating any part of it. I may have to increase the strength further or use Bayer."

You will. Most dish soaps are surfactants, and pretty solid ones like sodium laureth sulfate or sodium lauryl sulfate to go through grease (I'd have to look what ones Dawn actually uses), so the concentrations are fairly high.

Soaps aren't particularly easy to dissolve in water, and Ivory is usually sodium lardate (literally what happens when you make a salt of lard). It's not bad as soap (tallow is actually my personal preference for a bulking oil but they're not much different).

However, that doesn't disperse well in water and the saturation point is pretty low, so you won't get a good concentration.

Use the Dawn. It works better, you can concentrate it out to 10% or more easily, and 1% or less doesn't cause any issues.

https://homesteadandchill.com/emulsify-neem-oil-spray/

Most articles agree with this one and I'm not going to post a pile of articles just to post them or go with the scientific ones (they say the same in Science Speak). Proper emulsification is important, of course, and dosing. It's...going to interfere with reproduction where it doesn't kill outright, and it's not going to completely kill outright contrary to claims--particularly if the emulsion isn't perfect, and it's hard to do that at home in water.

No harm, no foul there as let's face it, it's a little hard to handle. It doesn't kill on contact, it's not that kind of pesticide, and even smothering to death takes time. Incomplete coverage means things take more time, or more applications. And eggs are not killed.

It's effective on soft-bodied insects and practically ineffective on many hard-bodied ones. Neem just isn't exactly what I'd call a hefty insecticide--or, why we use it indoors, as its minimal toxicity to pets and humans is helpful (again, keep away from cats).

If those are fungus gnats as well (I certainly have enough of the things), they're sturdy, but nothing to worry about. But we'd need photos to be sure. If they're fungus gnats...good luck with that. :-) As a general rule the average FG is reasonably harmless in small numbers, but not really something you want around in larger numbers as they can damage the plant if the number hits "droves." The only indoor plant you'd be likely to have that would be particularly susceptible to them, this time of year, is the pointsettia. I have several as general houseplants (I rather like them), have FGs, and don't have an issue with any real problems.

If it's something else, I'm sure we'll figure it out for you. Just send photos!

I think you're right the flying creatures are not aphids. After doing a little research I've become fairly sure they are fungus gnats. I've soaked the top layer of soil in a hydrogen peroxide solution - let's see if it has any results!

the good news I have to report right now is today I have noticed almost no aphids on my indoor plants. the fungus gnats appear to have become the main problem. haven't checked outside yet, and I imagine that will be a bit tougher.

I'm hoping within a couple of weeks maybe both pests will be gone on my indoor plants, if these methods work. I'll update here if I see results.

I don't want to enter into any controversies. I have something different to say about aphids. I have often had aphids in my greenhouse in winter. Eliot Coleman says, and I find it to be fairly true, that fertilising plants in winter brings much more aphids. To flush fertility out of the soil, it helps to water deeply once in a while, even if the winter conditions keep things damp so that you don't think watering is needed.

I go through and pinch aphids (my greenhouse garden isn't huge, and usually only one or two types of plants get big aphid infestations in winter). And then I spray them with a strong jet from the hose. These measures usually keep the aphids few and far-between enough that they can be washed off when harvesting.

Ants farm aphids. Sometimes getting rid of the ants with homemade boric acid and honey traps helps the whole situation. I think once the ants are not protecting the aphids, then spiders and little lizards eat more aphids. But they are not very active in cold conditions so this doesn't help as much in my winter greenhouse as it does in summer.

If I see cabbage aphids, I usually give up on the plant and pull it. These reproduce in dense yucky colonies that are just too much to squish or wash off, and ruin the plants.

I agree, nitrogen rich fertilizers promote new vegetative growth which aphids love to munch upon.