Apologies but I can't be at all positive about the aspirin fad bit and all its claims so I'll stick to just the issues of safe foliar feeding -

proper label instruction dilutions of only solutions approved and tested for foliar applications,

proper application methods (light misting, not drenching),

proper times of the day for applications (never in the direct sun or heat of the day),

and one mixture at a time (mixing often leads to negative interactions and the inability to determine which component did the damage). That addresses your question.

Failure to follow those guidelines can easily do more harm than good, even so far as to kill the plants.

Good luck with your plants.

Dave

PS: and for your experiment don't forget to have at least one or two control plants to support any conclusions drawn.

I have heard it before that supposedly ASPIRIN helps plants' immune system ( unknown way). Chemically Aspirin is some kind of acid and blood thinner. Some people also put it in cut flowers water along with little sugar. Again, I don't know the basis of it either.
We know that plants can absorb water via leave and thereby any thing that is fully dissolved in water can be absorbed. That has been said and advertised my MG for year.
But I thing the best way for the plant to uptake nutrients is via root system. I do , however,foliar spray Epsom Salt from time to time for fast action.

I cannot follow arguments for aspirin. It would seem to me that if one wanted to experiment one would try to find salicylic acid or a salicylate than aspirin.

Thank you, Dave and seysonn...

I will spray separately.

I am somewhat of a small gardener (aside from my stature =D) - I have 6 tomato plants (one Sweet Millions cherry, one Sungold cherry, one Cherokee Purple, two Pomodoro Pantano and a mystery plant - a gift from a friend - she said it was 'Cambodian') and some Thai basil, Greek oregano and a couple of Bell peppers. I have African Blue basil (to attract pollinators) and I also have let Fennel reseed itself (again, to attract pollinators).

This year, I have planted in my front yard which is a xeriscape (rotating away from the back and side yards - RKN problems)...since the only plant I have paired is the Pomodoro Pantano, I will use one of these as a control...Next year, I plan to build boxes in the driveway for the annual plants (3-4 boxes so I can rotate my crops).

As an old school computer programmer, I am aware of the perils of doing too many things at once and then wondering what change caused what result. ;-)

seysonn - When you say 'spray Epsom Salt from time to time for fast action', what are you referring to?

Note: As far as I can tell, aspirin (which breaks down to acetic acid and salicylic acid in water) has been researched and proven to be beneficial to tomatoes (and other crops as well)...here is one of the pieces of information I have gleaned from the ubiquitous Internet...

From the link below:

'CONCLUSION:
Salicylic acid is considered to be a potent plant hormone because of its diverse regulatory roles in plant metabolism. It is well-established fact that salicylic acid potentially generates a wide array of metabolic responses in plants and also affects the photosynthetic parameters which enhance plant growth and yield. It may, therefore be concluded that the sustained increase in the observed parameters expectedly culminated in maximization of the process of biomass accumulation leading to higher productivity, lycopene, vitamin C content of tomato fruit and as well as fruit Brix index.'

Here is a link that might be useful: Effects of salicylic acid on yield and quality characters of tomato fruit (Lycopersicum esculentum Mill.)

From human standpoint if aspirin was invented today it would not pass FDA. Anyone knows if plant and tomato itself does absorb it... i.e. will you be eating aspirin...