[Springlands]

I had a really bad infestation of white fly on my sweet peppers. To make things easier for the friend who was watering my greenhouse plants when we were on holiday I put the tubs of peppers on the floor of the greenhouse. On my return from holiday I discovered that the white fly had disappeared. Not complaining about that but just curious about why it happened.

[JayG]

Any Tagetes in the GH?

Perhaps your friend jet-washed the whitefly into oblivion?   

[Springlands]

Any Tagetes in the GH?

Perhaps your friend jet-washed the whitefly into oblivion?   

Probably the latter - I will have to get him back if I have any more problems. 

[JayG]

I've had my greenhouse for 4 years now, and have grown Tagetes at the base of some of the tomatoes each year and no whitefly seen at all - doesn't necessarily proves it works but given that I'm a bit sceptical about most forms of companion planting I'm happy to believe it does in this case! 

No greenfly either, but then again for the second year running I've barely seen a single one outdoors either (nor blackfly, nor indeed many ladybirds, perhaps not surprisingly.)

[Springlands]

We had lots of ladybirds at the start of the season and then they disappeared and the whitefly appeared!! The infestation did not seem to do the plants too much harm as I have a really good crop this year. They just look so unattractive.

[beesrus]

given that I'm a bit sceptical about most forms of companion planting I'm happy to believe it does in this case! 

I'm not sceptical at all, it's just a case of not expecting blanket success. After all, many chemical and barrier methods also fail on a regular basis with small scale growing. Other than for the planting of grasses like like sweet corn, part of the companion planting philosophy that is often not done properly, is not to plant crops in big mono culture blocks, and I'm often guilty of that. It's not just juxtaposition of other plants .. obfuscation and fog of war and all that.

I'm always amazed when I plant individual brassicas round and about, often inadvertently  , that they attract next to no attention from birds. What seems to work consistently well, say butterfly-wise, are nasturtiums and sparsely planted brassicas, but that does take room. What doesn't work at all, and gives companion planting a bad name is carrots and aliums, with the fly. I just don't think that can work at all on a well used allotment site where populations regularly over-Winter a few yards away. Unlike our gardens, allotments are a hot bed of disease, pestilence and marauding privateers
I think tagettes work better outside rather than in the greenhouse where barrier methods are so much easier. Put a net over the door, get the pollinating brush out, and that's that.

[JayG]

I think tagettes work better outside rather than in the greenhouse where barrier methods are so much easier. Put a net over the door, get the pollinating brush out, and that's that.

Surely there is nothing easier either in theory or practice than sowing a few Tagetes seeds in a pot (or in an oversize home-made planter to leave room for the toms in my case,) although I would have to reconsider the plan if and when the Tagetes 'trick' failed to work. 

There's very little science to support most of what are often extremely lengthy and detailed companion planting tables, probably because there is no money in it, but some of the suggestions at least sound feasible based just on common sense (attracting beneficial insects, repelling or confusing others, modifying the microclimate to suit the crops in question etc. - in many instances it's simply that avoiding monoculture, even on a small scale, improves the odds of at least some of your crops avoiding the attention of pests, as you mentioned in your reply.)

Some don't seem to have common sense on their side at all - nasturtiums may well be an aphid magnet but why deliberately create a flourishing breeding colony of them on your patch unless you intend to destroy the plants and their 'guests' before they actively start looking for your bean crop?

[Springlands]

I think I might have solved the whitefly mystery - lots of ladybirds and hover flies have re-appeared in the greenhouse. A benefit of keeping the doors open during the day!!. 

[beesrus]

Ah ... gardening logic, JayG. We all have our own logic
I don't see planting nasturtiums as deliberately creating a colony of pests. I see it as them happening to hoover up the pests that in reality will have been in the neighbourhood in any case, thus taking the pressure off one's veg. One could say that tagettes/marigolds, while having a beneficial effect, don't half encourage slugs who just love the younger plants.

How we then deal with the over-Wintering issue of pest colonies for the next year is all part of the process, and of course, we can't do anything about the practice of our near neighbours either.

I guess I could say I don't get the logic of neighbouring chemicals destroying the local colonies of good guys in the vicinity, but it's something I have to accept happens  on a site with many growers, and many of them swear by it. I have never understood that logic.
I don't see companions as a whole answer, just a small cog in a big wheel. Being chemical free, I still mainly have to rely on my barrier methods, along with companion/rotating/timing strategies that all add up.

[JayG]

That's the problem with having so little scientific research to back it up - logic alone can produce quite different conclusions! 

Agree with most of what you say, except that I still think that having 'hoovered up' the aphids the 'dust bag' needs to be emptied, either by destroying the plants and their visitors, or with suitable pesticides (which I accept you are unwilling to use.)

[snowdrops]

I plant Tagettes & or marigolds every year in my greenhouse around my tomatoes apart from this, guess what happened this year?