How much gardening is too much for chronic pain?

I did two things in the garden today. The first one was that I clipped one of the box trees in the front garden. That's the clippings you can see in my upside-down compost bin. The compost bin is currently upside down because it got moved out of the way like that when our fence was replaced. In an ideal world, I wouldn't have just tossed them on the top of the bin and left them there, I'd have mixed them in with the rest of the bin's contents. Unfortunately, between clipping the hedge and clearing up the clippings, I did one other thing in the garden:

I re-dug the vegetable patch because it had been flattened when the fence was put up. I didn't even do a particularly good job of it. I left most of the chunks of earth large and unbroken and it only took me about 5 to 10 minutes - or at least, that was my perception (time does fly when I'm gardening). But by about three quarters of the way through, my lower back was using twinges to tell me it wasn't happy. I should probably have stopped the moment it started to hurt, but I really wanted to finish what I'd started - also, I have no guarantee that the damage wasn't already done at that point and that I'd have any fewer twinges bending down afterwards or would heal quicker if I stopped the moment the trouble started. Also, I really didn't want to leave clippings all over the front garden for yet another day, so I carried on and cleared those up.
My desire not to leave things unfinished so I don't have to do them later is clearly higher than my desire to look after my chronic pain.
It's tricky though. Mindfulness meditation suggests that I should be kind to myself. But what is kind to myself? Is it kind to myself to stop doing something the moment it starts hurting? If so, I wouldn't work at all (mind you, I'd have no issue with that if I had the money not to work). Or is it kind to myself (my usual approach) to make sure future Laura has an easier life because present Laura has thoughtfully planned and done things for her? I often find myself pleasantly surprised to discover that past Laura had done things for future Laura, that present Laura had forgotten all about and is now benefiting from, and it comes as a pleasant surprise to discover how organised and thoughtful I was (that particularly applies to filing things properly when I get them).
Of course, the downside of this is it means I have a tendency to battle on through pain - for instance I continue to work and save for my pension and my future despite the fact that, as a rough rule of thumb, every minute I spend working adds to my pain (it doesn't necessarily increase it up and up, but it does cause me repeated pain which I wouldn't necessarily be in otherwise and which stays with me and causes me problems after I've finished). It also means that I look like I cope brilliantly - or possibly that there's very little for me to cope with in the first place, which often means I end up doing more and more, including things I probably really shouldn't be, like the washing up (that causes me a lot of problems).
Anyhow, the key point is that I gardened until about quarter or an hour beyond the point at which it started hurting, and that's very definitely me done gardening at least for the day and quite possibly for the weekend, or even the week. There's another bush I'd have liked to take down:

It's not happening today though.
So, how much gardening is too much? I've been thinking about it while I was writing this, and I've come to the conclusion that for me it's like this:

Know your chronic pain. Observe what happens to your body when you do things. Then make choices about what trade-offs are worth it to you. Also, if you can split a job up so you do a bit of one physical activity for a while followed by a bit of a different one, that helps. For instance, if you need to spend an hour weeding, an hour mowing the lawn and an hour clipping bushes, it can help to do 30 minutes of weeding, followed by 30 minutes of mowing, followed by 30 minutes of clipping, then start the cycle again (or 15 minutes or 10 or even 5 if that's how your back works and you can bear to switch tasks every five minutes). I've now discovered that even 5 - 10 minutes is too much digging for me at the moment (although I have joined the gym, so if I'm lucky, that may change as my body gets stronger). In retrospect, I should have started with a couple of minutes of digging and interspersed my digging with clipping (which I can do for quite a long time without pain). But it didn't occur to me that I wanted to dig until I'd pretty much finished clipping. Also, I had no idea that 5 - 10 minutes was too much. Then, on top of that, I like starting gardening without thoroughly planning everything I'm going to do. I also like concentrating on a single task for longish periods, so constantly switching is quite irritating for me. On the other hand, perhaps switching about would have kept me going longer, which would have been good for my goal of doing more gardening than I got through today, but might also have upped my irritation levels (having to switch about instead of doing it in my preferred style). 

Update from the following day (Sunday): I should have stopped earlier. I should have done no more than 2 minutes of digging. I'm still in a lot of pain (in different places from where I had the problems yesterday), and digging the veg patch wasn't worth it. I will try and remember to limit myself to two minutes a day when I get better again (possibly with an alarm, so I don't just keep going). How I feel today was not worth 10 minutes of digging.