g'day,

no side efects that i can imagine, outside of there is no need for peat, there are better products around, yes the potting mix isn't such a bad one but how about buying some composted organic material we have product bagged in retail outlets over here so imagine the same would be over there? maybe your local refuse transfer site has some recycled organic material? many do.

also most of us have clays that can be helped with a liberal dose of gypsum around the sides and the bottom of the hole. we ahve clay soils and when i plant trees/shrubs i use spent mushroom compost along with the gypsum, works for me.

len

Here is a link that might be useful: len's garden page

Peat moss is probabaly one of the worst soil amendments for clay soil since it holds too much water when wet, inhibiting good drainage and if it dries out, is almost water repellant thus creating dry pockets in the soil. Compost, aged manure, fine wood bark/pine chips, or shredded leaves or leaf mould is far superior to peat moss. To answer your question, "yes" any amount of peat moss in clay soil is too much. In sandy soil peat moss is a benefit, but not in clay.

I've found the opposite in my clay. I found mixing a good 3 inches of peat moss into the top 6 inches worked wonders for my garden. Root development and plant health was much better that year and subsequent years. I would top up about an additional inch every year after that.

2 things to keep in mind...

1)Peat moss has no nutrients for your garden. It is a great soil ammendment for clay soil but not a fertilizer. That may not matter since clay soil is supposed to be more fertile soil than sandy soil anyway.

2) Do not use peat moss as a mulch because it will be hard to wet. Always mix your peat moss into the soil.

I've seen people who dig a hole for blueberries, fill it with 100% peat moss and don't have a problem with it being water repellant. I don't know how they manage it but apparently it works. I've just never had luck with pure peat moss. In my experience, I have to mix it with the clay soil in order for it to work.

I have seen more plants die from peat moss in clay than almost any other soil amendment cause. I guess it may be how much you add and how well you mix it it, but still there are much better alternatives.

Gypsum really does nothing for soil texture unless the problem is because of sodium. Sodic soils become mucky...gypsum helps alleviate that, but it's a chemical process not a physical one. Gypsum's ability to work magic on most clay soils is one of those long lived gardening myths.

Adding soil amendments of any kind when planting woody trees or shrubs is discouraged when planting hole by hole. It is far better to dig a nice wide hole (basin shaped), set your plants high, and backfill with the native soil. Clay or otherwise. Unless your site doesn't drain or the clay is blue or gray colored, clay usually poses no problem for plants. Believe me, I know this for a fact, lol.

If you were to rototill a whole row, you could add some bark soil conditioner (found at the big box stores) as your amendment for the entire area, rather than just in the hole. That would be much better than peat.

One of the biggest problems with amending a planting hole with anything that will make that soil easier for water to get into, and not amending the rest of the soil is that water will just accumulate in that planting hole and drown the plants. You create a place that is easy for water to flow into and it cannot get out. If you live in an area that has lots of deciduous trees those leaves that fall every year are a much better source of organic matter than peat moss, which is a non renewable resource, has no nutrients, and creates the need for you to spend more money on the nutrients the plants will need to grow, if they don't drown.

I'm late to this and also not an expert on anything to do with gardening, all I know is what has worked for me.

When we first started gardening in this coniferous forest with little topsoil and clay soil I used topsoil, peat moss and old sawdust to try to create something that looked like soil rather than concrete. I also did a cover crop on part of the garden which DH tilled it in.

One of the problems with peat is the acidity which worried me at first because I thot the soil might already be too acidic due to the tree needles which formed most of the thin topsoil. Great for blueberries but not for everything.

I do not think the peat moss caused any problems and did improve the soil over time. I added some each year for several years along with a lot of other things such as mushroom manure, compost, wood shavings. We are limited as to what's available here in the sticks.

As others have said your problem will be with drainage so it's better to dig a trench than individual holes - the bigger the better.