It is worth doing a good job of putting supporting posts in, as it is such a nuisance if the raspberry canes fall down. Posts are needed in the kitchen garden to fix the wires along which fruit canes can be trained. When in full leaf the canes are quite a weight, (particularly if it rains & the leaves are wet) and if in a windy spot, a lot of pressure is put on the post.
Posts can usually be found in garden centres, but Amazon have some like these (it is an affiliate link):
To hold the post up, a long end needs to be firmly fixed in the ground as an anchor.
At least 2′6″ of the post, preferably 3′ , should be in the ground, depending on the soil type.
Dig the hole 3′ deep, shove the post in & back fill with a little soil at a time – 4 or 5″, then thump it down. Thumpers were made in the old days but they are hard to find now.
Use the blunt end of a stake to thump the soil down around the post, but it must be thumped evenly, or the post will keep moving. Let the thumper fall straight, & watch your hands – wear gloves. Put another 4″of soil in & thump again. Check the post is straight as you go, with a
spirit level. If not, thump a bit more on one side than the other, to straighten it up.
You can back fill with 1″ chalk or brick rubble (particularly at the bottom of the hole) instead of soil, but make sure it is small enough and that it breaks down as you thump, so that it goes tight.
berry support post
To fix a post in firmly, there should be a third more soil in the hole with the post, than you took out – if you have thumped it down well enough!