It hold tell you on the Growbag what the actual contents are if not do a Google search...

Hi Diane. Sand has no nutrients, and growbag compost won't have any drainage problems, so I don't understand why you're adding it. If you've been advised to put sand in raised beds for some reason, then you should be putting a shallow layer in the bottom of the bed (for drainage), not mixing it with compost.

For plants to thrive, your raised beds will need a lot more than growbag compost. Do an internet search to find the best mix. :)

it depends on the make Diane, some are purely peat others are a mixture of peat, humus and loam.
the peaty ones once dried out are a problem to rewet.

Agree with Rosierose you don't need sand... What you really need is lots and lots of compost, whether from your own compost bins or bought in. Organic matter is the key, and Growbags are designed to grow veggies and/or flowers in for a very short period. When Bulba created our raised beds, many years ago now, he put turned over turf in the bottom then so less than good soil and filled up with good soil full of organic matter. Given the way he/we were creating the beds the building of the actual beds had to be done as an organic exercise, as he built the bed up he had to keep adding the soil to support the dry stone walls and then building above the level of the soil and adding more soil... interesting process but it worked! Today you would never think the area where the different raised beds are was original grass and level!

Sorry folks, but these methods are all describing decent top soil and not the substandard clay stuff left here and other places in town, by builders who scrape off the top soil and sell it for £100 a lorry load to people who have been cheated in the same way.
Sand is essential for plant roots to spread and thrive on.
My Gerbil compost has given me excellent plant results in the 2 years I have been making it. I just ran out of old potting soil until the Tomatoes are finished, thats all.

Garden soil is ground up rock. It does not contain nutrients, these are fragments of plant residue that stick to each grain. My Growbag soil is ok in the compost making box now, I just had to add the essential nutrients, and lots and lots of water, giving it a good stir. People with good top soil dont know what its like, struggling like I have had to, for 16 years.

Diane when we moved here the top soil was little more than an extremely sandy loam... you simply have to work with it and feed it, now it is an extremely nutrient rich soil. Growbags are not going to do that! It isn't what they are designed to do, sorry.