How do you know when a plant is really dead or just needs reviving? (I'm a real novice!)

[Lalaland50]

I've got a few plants that aren't springing back to life...I've attached a couple of photos - one is a hebe and the other is a Nandina Domestica (sacred bamboo)...(this one's been in the shade and I'm wondering if it hasn't had enough sunlight and has just withered away...I really want to save it but not sure if that's possible)..just wondered if there was anyone with some experience that could shed some light (ha!) on my dilemma...
thank you.

The Hebe seems alive, a bit scraggly, but not dead. The Nandina appears to have a few green leaves, so maybe all is not lost. You could cut back the dead branches and see if it sprouts out anew.

Thanks. Should I do anything with the Hebe?

All the branches seem a bit dead on the nandina - do I literally cut them all off so I'm left with just a tiny bit at the bottom?
(sorry, complete novice here and learning very slowly)

Cut off most of the brown bits of the nandina leaving the few green leaves. I would say the pot it's in is too small and possibly a combination of the late frosts we've had and underwatering when we had those few very weeks have done the damage. Cut it back and see how it fares for a few weeks and if it seems to be reviving then look to re-pot it.

I've got some nandinas I put in earlier this year and they've got some frost damage as they aren't yet fully established.

To answer your original question:

A plant is really dead when:

brown stems are brown all through, or break with a sharp snap. You can scratch the bark to see if there's a green layer underneath.

there's no sign of life above ground, and the roots are soggy and rotten

If it's a bulb , the bulb is rotten and squashy.

If it's a cactus, it's hollow inside

If it's a seedling, all the leaves have dried up to straw texture.

Thanks for this, that's really helpful. Can I put the nandina in the ground? would it be happier there?

I'd see if it revives in the pot first once you've cut it back. Ideally you want to plant shrubs out when they're dormant. If it revives you could plant it out in the autumn. Having said that I once overhauled a large bed and planted it up in August - used a sprinkler in the evening to water thoroughly as it was really hot during the day.