heathers tend to prefer acidic conditions some will cope if neutral soil. dig some multipurpose compost into the soil before you plant them.
cant help with the salix sorry.

Salix (Willow) needs plenty of space, will grow anywhere.

Heathers best in large pots or containers, planted in
Ericaceous compost. Can be moved around to make a good show when in bloom.

Sorry Diane but mine do well in the ground and look great. If they the ones in flower now they will be ericas which are not as fussy about acid soil as the summer flowering callunas, but they still do prefer it. They prefer full sun and most varieties will make a clump of at least a foot across in a couple of years. They don't normally exceed a foot in height. (sorry I'm not very metric) If you want to put them in the ground dig a larger than normal planting hole and fill with ericaceous compost as Diane suggests.

The Salix you've bought is usually sold as a half standard, that is, on a straight stem with growth at the top. If that's what you've got, plant somewhere the soil doesn't dry out all the time, but where it will get some sun, and plan to allow for a spread of topgrowth up to 6 feet all round - although they can be clipped back just as growth begins to keep them tidier, less floppy and large.

Me now thinks its best if Trudje gets her garden soil
properly analysed, as she may lose plants expecting
them to grow in the wrong soil conditions.
We all fall into this trap when young !
Willow would be alright anywhere because it grows
on the banks of streams, anywhere.
Heathers only grow naturally in acidic soil.
I advised getting Ericaceous compost and putting it
into a container of some sort because thats the
right soil for the plant, and can be topped up with
the right food after 3 months.
Heathers are beautiful plants, - get neglected.

More thinking. Trudi when you look at plants to buy, think about them and where they originally grew in the natural state. I know its not easy.
Therefore the Primula family came from Primroses - some GCs actually still label some of them as 'Primroses'.
Primroses grow naturally in shady woodland, in ground that has had centuries of leaves falling on it.
Have you got an area in your garden that emulates these growing conditions ? If so Primulas will thrive in that place, and not in clay soil in blazing sunshine, where Rose plants are happy, as they are in the wild.
Heathers grow naturally on heathland hills, you can see them from coach trips. They are not at the seaside.
Old editions of RHS Plant Encyclopaedias can be found in charity shops for £4 ( New they are £35) Encourage your daughters to do the research, and they will remember when they have gardens of their own !