Tomatoes and potatoes - inappropriate bedfellows?

[Kaiya]

I have a 1/4 allotment (6m by 9m) - dinky compared to some grapes but more than enough for us, work-wise. I've diligently set up five beds for rotation:

1 - potatoes
2 - legumes
3 - brassicas (and squash)
4 - onions etc. (we love them - need a whole bed!)
5 - root veg

I'd like to (attempt to) grow tomatoes on the allotment this year - determinates - using the polythene tent idea as blight got everyone last year, even the grafted trio I had in our garden (which backs onto the allotment). I don't have a greenhouse, and although I have two blowaways I also want to try aubergines so need one for that, plus they are my only cat-safe seed sowing space (all windowsills belong to cats, I've been assured!)

I know planting tomatoes next to potatoes is not a good idea (though not sure how risky it really is). However they are the same family, so rotation means they should be together, the soil there is already tomato-suitable and it's convenient as the rest of the plot already has stuff intended to go in it. Plus our space is so tiny they will always be within about six feet of each other regardless of where I put them. Putting the tomatoes at the other side of the plot will probably just put them closer to nextdoor's potatoes.

So really my question is - should I worry about my tomatoes in-a-tent being in the same bed as my potatoes not-in-a-tent? Or just do it and see what happens?

[RedThorn]

Always been told even as a kid never put potatoes and tom's together (actually was told never ever even in the same soil). Never done it and unlike me usually, never questioned it. Besides diseases, not sure why to be perfectly honest

[Alison]

I understood it was due to concern about risk of disease as they're both liable to get the same things (usually blight!). I don't bother growing tomatoes outside now but when I did I had them in the same rotation package as the potatoes although in a separate bed they were only a few foot away and both in the soil so I'm not sure what the difference would be. I do a 4 year rotation (ish) with spuds, beans, brassicas and roots which seems to balance OK for us.

[PAULW]

Tomato's and potato's are related so the same disease will affect both so if you plant them together you are doubling up on the risk.

[Potstubsdustbins]

As I grow in containers all the plants are in different compost but by virtue of the size of my garden my spuds and toms are very close together.

As to blight I think its airbourne and if so a few feet ar'nt going to make a difference. Perhaps you may think of growing your toms in pots/buckets then the close distance wouldn't be a problem realising if you get blight everything is going to get it anyway.

Colin

[snohare]

I think you have already answered your own question, haven't you ?
In potatoes you want to encourage the tubers, in tomatoes the fruit, so the soil will actually have very different ratios of nutrients taken out by the respective plants, and if you treat the plots they are in as being all the same afterwards, you may be in for a shock. That might be the origin of the old proscription, but frankly I cannot see it being disease.
The main disease you are worried about is blight, and there are literally thousands of different strains of that going about now that it reproduces sexually. So whatever you plant, it is in the lap of the Gods as to whether it will succumb or not. Given the untold billions of spores that might be floating about during a Smith Period, travelling hundreds of miles on the winds of a thunderstorm, a few yards difference are not going to make much difference.
What might make a difference is keeping the spuds somewhere they might dry off a bit quicker after rain - so maybe in a windier spot.

[Kaiya]

Ah I'd assumed they liked the same type of bed (being the same family) - so lots of organic matter. Where I'd read about not putting them together it did list just blight as the issue - in that potatoes get it and then decimate the tomatoes (whereas the potatoes might survive). I'd never heard of the soil being an issue, other than blight persisting in it.

So sounds like I shouldn't worry about how close they are (since 1 mile would be too close lol) but should perhaps give them their own tomato bed in the 'I don't know what to do with this bit' area of my plot.

[Two_Sheds]

I'd never heard of the soil being an issue, other than blight persisting in it.

No, blight doesn't persist in the SOIL. It can only survive on living plant tissue ~ theoretically it could survive on any volunteer spuds that remain in the ground, but tbh ... I always leave volunteers in the ground, and I've never had blight on my spuds (although I can't grow tomatoes outside as they ALWAYS get it).

You can compost blighted foliage too, because the spores only survive on LIVING tissue, not dead & rotted plant material

[alex-adam]

This link may be of interest:

List of companion plants - Wikipedia, the free encyclopedia

[snohare]

No, blight doesn't persist in the SOIL. It can only survive on living plant tissue ~ theoretically it could survive on any volunteer spuds that remain in the ground, but tbh ... I always leave volunteers in the ground, and I've never had blight on my spuds (although I can't grow tomatoes outside as they ALWAYS get it).

You can compost blighted foliage too, because the spores only survive on LIVING tissue, not dead & rotted plant material

No, this is one instance where I would go along with the old cant.
You fail to distinguish between the infectious, actively destroying structures of blight, and the dormant spores which are the end result, and which later give rise to another generation. Spores are basically seeds, with an extremely difficult to penetrate outer shell that protects against all sorts of bacteria and other pathogens. They are admittedly often rendered non-viable by UV and various chemicals, and I daresay maybe microscopic beasties - but why take the risk, given the potential outcome ? Buried in the soil at the right depth, dug up at the right moment, who knows when they may be lurking. Don't forget, spores are things that have been shown to survive the hard radiation of space, and the heat of re-entry.
What saves us in this situation is that spores, in being so incredibly resistant to stresses, are also vary hard to switch into active mode ("germinate", if you like), but I certainly wouldn't risk giving them a headstart. Cutting back on the numbers present is a no-brainer, risk is always a number game...
I'd bet a pound to a penny that you can get areas of a hot compost heap which might trigger spores into activity if there was enough blighted materiels there - albeit rarely.

[Two_Sheds]

You fail to distinguish between the infectious, actively destroying structures of blight, and the dormant spores which are the end result

"The fungus can also produce resting spores (oospores) in the plant tissues that can contaminate the soil. Little is known about their survival and their potential as a source of the disease. The investigations into oospores are continuing and more information may be available in a few years." Potato and tomato blight / Royal Horticultural Society

Garden Organic says this: "Infected potato haulms (foliage) may be composted in a good active heap. The likelihood of resistant spores being present is very slim. "

"Composting: Blight infected foliage can be composted. The blight fungus requires a living host to survive. When put in the compost bin potato foliage will die quickly and with it the fungus. Infected tubers should not be composted as they may re-grow"

Factsheet about potato blight

As with everything, read all the advice, and make your own mind up.

[snohare]

Granted, I am assuming that the spores, either sporangia or oospores, are like the spores of other species such as anthrax, with a wider envelope of survivable conditions than normally assumed. That's an assumption taken due to background context, and it may be wrong. You are right to call me on that one.
But I will bet you, now that there is sexual variation in the blight strains, there will be versions of the spores out there that will survive in conditions that previously were considered safe. Natural selection will do this. You just watch this space. It's like Bird Flu - it is out there in the environment, mutating, filling every possible niche, and just plain lurking, ready to wreak havoc once the right combination of conditions occurs.
Plain fact of the matter at present is that things are changing, and we don't know what is happening, or what nasty surprise may come next. Thank Heavens blight doesn't mutate as fast as flu !