They are highly toxic if ingested, but no, they won't harm anything in your garden, and they won't harm you provided you don't intend to make a salad with the leaves, which is something I'd also say about Rhododendron and Prunus varieties. Watch the sap when pruning though, that can be highly irritant to the skin. They are though, not entirely hardy, may need winter protection, specially in a very cold one.

Thanks bamboo, No I won't be making any salads with the leaves, but I do appreciate your advice on pruning, which is down to Mrs treetop lol. Seriously much appreciated my friend.

Hi, I agree with Bamboo, but there is 1 variety of Nerium oleander that is hardy down to 10f, and that is 'little red', I mentioned this in a comment to a question asked on 2 may by Dianedave, I didn't name the variety on there, but if you care to take a look, I have given some cultural advice as well, Derek.

Nerium Oleander is not like a Rhododendron. It is in the dogbane family Apocynaceae and is one of the most poisonous plants known. It's lethal. Rhododendron is in Heath Family (Ericaceae), no relationship. All parts of Nerium Oleander are poisonous and contact with the skin can cause dermatitis. Honey made from this plant should not be eaten and smoke from burning is toxic. Be extremely careful with pets and small children.

There's an interesting story about this plant being used to commit murder at the Myrtles Plantation, Francisville, Louisiana. An entire family was wiped out, but their ghosts is said to haunt the place to this day, which is now a 'Bed & Breakfast. This story has been peddled for ages.

Thank you folks, this complete amateur really does appreciate all your advice and comments.
Okay, I said in my original post "Am I being paranoid". This morning I have developed a very serious rash on the inside of my thigh, I also have a tummy upset this morning, is it possible the rash and me handling the Nerium Oleander could be related? I did immediately take a long shower afterward.

No, Treetop, not unless you chewed on a leaf, or managed to smear the sap on the inside of your thigh, or broke a leaf or stem, got the sap on your fingers and put your fingers in your mouth, at the same time managing to smear it on your thigh. I've planted several of these over the years and never had a problem of any sort - I've also pruned them, I just wear gloves, never had a problem then either, and if anyone was going to have a problem with a plant, it'd be me - I can no longer cut ivy back because I can't breath if I do, its a full breathing mask job these days, for instance. And I get contact dermatitis from brushing against conifers.... plus a few other reactions to other plants.

If all you did was take the plant out of its pot and place it in the soil, without damaging any of it, including the roots, and wearing gloves, whatever you're experiencing now has some other cause, so go to the docs...

I'd just add here that other plants are also toxic if consumed, and which family of plants they belong to is largely irrelevant. For instance, Aconitum (Monkshood) belongs to the Ranunculacaea and is highly poisonous, one of our most poisonous plants in fact - but buttercups also belong to the same family, and aren't toxic, so which family a plant belongs to is not a useful guide to toxicity. Prunus laurocerasus, which occurs frequently in our gardens, can kill people if you use the stones from the fruits, the leaves are toxic, Rhododendron is toxic, daffodil bulbs are toxic, and Monkshood (as already mentioned) is highly poisonous, rhubarb leaves are toxic, you can kill someone with lily of the valley, and so on, so don't panic Mr. Mannering! If you want to find out more about poisonous or toxic plants in general, including nerium oleander, and for the sake of sensible perspective, have a look a these two websites

http://www.thepoisongarden.co.uk/default.htm

and for a list of plants regularly grown here which are potentially harmful (including oleander) see here

https://www.rhs.org.uk/advice/profile?pid=524#section-4

Of course the sap runs through the entire plant, root to crown. Oleander is one of the most poisonous plants known. I'm not trying to win an argument here and I won't belabor this any further. I'm simply trying to caution you to be extra careful.

Of course the way it affects you, is different from how it affects me. It depends on your own immunity, genetic make up and allergies. This plant contains many toxic compounds some will slow your heart.

Here is an exert from "Plant Encyclopedia" about oleander:

'The toxicity of oleander is considered extremely high, and it has been reported that in some cases only a small amount had lethal or near-lethal effects.[16] The most significant of these toxins are oleandrin and neriine, which are cardiac glycosides.[16] They are present in all parts of the plant, but are most concentrated in the sap, which can block out receptors. High-risk circumstances of exposure include children playing with the ornamental shrub, as well as adults or children tasting, chewing, and ingesting portions of the plant [2], and inappropriate medicinal use of plant infusion.[8] Oleander bark contains rosagenin, which is known for its strychnine-like effects. The entire plant, including the nectar,[17] is toxic, and any part can cause an adverse reaction. Oleander is also known to hold its toxicity even after drying.

Here's the link: take care

http://www.theplantencyclopedia.org/wiki/Nerium_oleander

Thanks Bamboo and Bathgate. It must be my age then, the only other alternative is, I must be falling apart. Oh, the joys of getting old. Seriously though, thanks folks. You have helped put my mind at rest.

It may be everything bad stated above but Kew Gardens' website also states the medicinal uses:
"Oleandrin is used for treating cardiac conditions in patients who cannot tolerate digitalis. In traditional medicine, the leaves have been used for a variety of medicinal purposes, including the treatment of heart diseases, as a diuretic, antibacterial, and against snake-bite. The roots have been used externally in traditional medicine for treating cancer, ulcers and leprosy."

I'm not convinced about planting it out - I grew one once but in a pot so that it could be brought in over winter. They are (generally) Mediterranean plants - grow like weeds in (former) Jugoslavia.

Interesting info, Urbanite, I've never looked that up. I'm sure many 'poisonous' plants have been used in medicine, in small amounts - Yew is what tamoxifen (cancer drug) was originally created from...