Just had 25 plants delivered and need to get planting. The soil I'm planting into is predominantly clay. I have been advised to mix in gypsum and fertilizer. I have several bags of putting mix that I haven't used yet and was thinking of adding that into the mix rather than gypsum and fertilizer and so mixing the potting mix and clay together. I'm planting viburnum only small, 140mm pots and gardenia 140mm pots.
Do you think I'll be safe going this way with my earth as don't want them dying! Also I.only get morning sun and the area is usually damp.
Thanks for your help!
You'll definitely want to use gypsum to break the clay. Part of the reason clay doesn't drain is because the mineral particles are so tiny and pack themselves together so tightly that water can't pass through. Gypsum actually binds clay particles into irregularly shaped "crumbs". The gaps between the crumbs are big enough for water to pass through.
But if the area is usually damp the clay might be too big a problem to fix with a few bags of gypsum. In a worst-case scenario you might also need to install some drainage and/or replace some of the clay with new soil.
One way to get a sense of things is to dig a hole 30cm x 30cm wide and 30cm deep, fill it with water and let it drain overnight. Then fill it again and see how long it takes to drain. If the hole drains within half an hour to an hour that's good. If the water stays there for hours you have a problem.
Potting mix is formulated for potted plants and is not suitable for garden beds. Luckily, you can also get bagged garden soil and organic compost. It's easy to remember: potting mix for potted plants and garden soil for garden beds.
To break the clay properly you will need to mix the gypsum through thoroughly to a depth of at least 10-15cm, and then mix through the organic matter and leave it for a few to several weeks for the gypsum to take effect. Garden soil or compost won't break the clay by itself (and neither will sand).
If the clay ends up proving too difficult or expensive to deal with you can always cover it with some nice pebbles or river stones and put your plants in nice big pots on top of it. Let's hope it doesn't come to that!
Welcome to the Bunnings Workshop community. Thank you so much for joining us and sharing your question about what are the best planting conditions for your new plants.
It's great that you've received amazing advice from @BradN on how to treat and prepare clay soil. I totally agree with the recommendations that have been made. Doing a soil drain test is one of the best ways to find out if you have too much clay in your soil. I'm afraid adding potting mix will not make much of a difference if the soil is waterlogged.
Please keep us updated with your progress, we are keen to know if the water will drain away.
If you need further assistance, please let us know.
Thanks very much Brad I'll take those factors into consideration and do the drainage test.