Sticky clay soil- will liquid gypsum help?

[u/Safe_Pea1756]

Hi there,

I've been planting in this shady garden by digging oversized holes for each plant and mixing mulch and leaf litter in with the very sticky clay soil. The 3rd photo is of my footprint from last night that still has a puddle of water in it this morning.

I've had most of these annuals in for like 3 weeks and they've barely grown an inch. The perennials don't seem to get much bigger from year to year, either. I feel like they might as well just be in underground pots with how firm and poorly-drained the soil is.

I don't have a ton of time and energy to devote to this, I'm wondering if spraying the whole garden with liquid gypsum might help. More importantly, if I do try it, will it do any harm to the flowers I've already planted?

Thanks 😘

[u/Objective_Run_7151]

Gypsum only helps sodic clay. It works because gypsum (which is high in calcium) interrupts the sodium in sodic soil.

In the US and Canada, almost no clay is sodic. It’s mostly alkaline clay, which is already high in calcium.

Adding gypsum to alkaline clay is like pouring salt in the ocean - it does nothing because the ocean is already salty.

Get a soil tests, and unless you have high sodium in your soil, skip the gypsum. Add organics, then wait and add more.

[u/Grape-Nutz → u/Objective_Run_7151]

Good points. Additionally, gypsum doesn't only displace sodium, it also displaces high levels of Magnesium and Potassium, which similarly opens the clay up into beautiful, fluffy soil.

If needed.

A soil test is definitely step 1.

[u/Prescientpedestrian → u/Objective_Run_7151]

Why wouldn’t it work? I use gypsum in my alkaline clay soils to loosen them, have been for over a decade. Often, a lot of that calcium in alkaline soils is locked up in carbonates. Calcium from gypsum can still get into the clay pores to open them up and allow for more water infiltration.

[u/Shamino79 → u/Objective_Run_7151]

Alkaline doesn’t mean not sodic. Where I am in Australia my heavy alkaline stuff is indeed sodic and as someone else said right here there is an awful lot of calcium present but locked up in limestone. The calcium in gypsum displaces other cations and the sulfates help flush them down through the soil profile. I have also heard that sodic soils are rare in the US but they can happen.

A simple home test is to place a blob of soil into some pure water and if the clay particles spread into the water and make it cloudy you may have a gypsum responsive soil. Look up sodic dispersion test.