Moist soil and planting

TheGardenerFromMars · March 2023

When planting new plants people often add compost to the planting hole, but what's the relationship between this added compost and moisture retention?

I'm planting some plants that like moist soil, so if I'm planting into a bed with moderately heavy clay soil, should I increase or decrease the amount of compost added when planting in order to help keep the soil moisture levels as high as possible?

punkdoc · March 2023

I wouldn’t think about moisture retention, just that compost improves soil quality.

TheGardenerFromMars · March 2023

Okay, thanks. So is a thick mulch the best option for keeping soil moist?

gardeningzilla9XtYVKec · March 2023

Adding compost to the planting hole can help improve moisture retention by increasing the soil's organic matter content.

For plants that like moist soil, adding more compost can be beneficial as it helps retain moisture. However, be sure not to overdo it as too much compost can make the soil too dense and waterlogged.

Fairygirl · March 2023

As @punkdoc says - compost improves structure @TheGardenerFromMars . It doesn't help drainage as such. Any organic material will improve the structure of clay and make it more open- leaf mould, manure, compost etc. It does that with any type of soil [improving structure] - it makes light sandy soil more retentive, but it all takes a bit of time - it isn't instant. Mulching with it is the method though.

I disagree with quite a lot of the previous post above. Compost won't make a soil more moisture retentive, unless it's one of the J. Innes types - which are soil based.
Your climate is also a factor. In wetter areas, it's even more important that the structure is good. Plants that like a moisture retentive soil still need some decent drainage. Even bog plants need that.

What plants are you considering?

punkdoc · March 2023

Adding compost will not make the soil waterlogged, @gardeningzilla9XtYVKec

Fairygirl · March 2023

Indeed @punkdoc. That was my view. Very misleading.

gardeningzilla9XtYVKec · March 2023

I said too much compost can make soil too dense and waterlogged.

Compost is a great way to add organic matter to soil and improve its fertility, but if it is added in excess, it can actually harm the soil structure and negatively affect plant growth.

Fairygirl · March 2023

gardeningzilla9XtYVKec said:

I said too much compost can make soil too dense and waterlogged.

But it doesn't. I'd have even heavier soil in every bed and border if that was the case, and so would lots of people who garden in clay in wet areas of the country.
I'm not sure how you're arriving at this conclusion, unless it's down to using loads of the type I mentioned, as they are soil based, and therefore heavier than multi purpose composts because they serve a different purpose.

You've also pressed the 'like' option on @punkdoc's post which is even more confusing.

Liriodendron · March 2023

I guess the problem here is that "compost" means different things to different people. As @Fairygirl says, if you mean commercial soil-based compost, that's not an appropriate material for a mulch. But a mulch of organic material like garden compost, or composted green waste, or leaf mould, or well-rotted manure, is bound to improve your soil's drainage and the health of your plants.

The problem of actually mixing compost in the planting hole is that, in clay soil, you are likely to be creating a "sump" round the roots of your new plant. Far better to dig in well-rotted organic matter over a much wider area, and/or to apply it as a mulch.

Perhaps that is what @gardeningzilla9XtYVKec means...

robairdmacraignil · March 2023

This discussion on adding compost to the hole that is being used for planting reminds me of advice I think I saw on gardeners world the TV program. The point was made in relation to planting trees and it was that adding too much compost to a planting hole can lead to the roots being happy in that planting hole because of the extra nutrients in the compost to such an extent that they are slower to reach out into the wider soil area and so take longer to properly establish the larger root structure required to support optimal plant development. I prefer to just add compost to the soil surface and let the worms do the work of bringing it deeper into the soil and improve its structure as they do so.

Happy gardening!

Moist soil and planting

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