How to fix a veggie bed that won't drain
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How to fix a veggie bed that won't drain
A bed that turns into a puddle after decent rain and takes days to come good is a drainage problem, and it matters more than most people think, because roots need air as much as they need water and soil that stays saturated has no air left in it. That's where yellowing leaves, stunted growth and root rot come from, and you can feed a waterlogged bed all you like without any of it helping.
Test it first, so you know what you're dealing with
Dig a hole about 300mm deep and 300mm wide, fill it with water and let it drain away completely, then fill it a second time and watch that one. Soil that's draining properly will drop somewhere around 25 to 50mm an hour. If the second fill is still sitting there hours later you've got a real drainage problem, and if it drains before you've put the shovel away you've got the opposite one and the bed will be drying out too fast.
Do the test when the ground is neither bone dry nor already sodden, because both will give you a misleading answer.
What actually helps
Organic matter is the one that does the work. Compost, aged manure and leaf mould all open heavy soil up as they get worked through it and as the worms move it around, and it's a slow fix rather than a weekend one, but it's the only one that keeps improving instead of wearing off.
Gypsum is worth trying if your soil is genuinely clay, because it makes the clay particles clump together into crumbs that water can move between. It's slow, it doesn't suit every clay, and the honest test is to drop a dry lump of your soil into a glass of water and leave it overnight. If it collapses into a cloudy mess, gypsum will help. If it stays as a lump, it won't, and you're better off spending the money on compost.
The one thing not to do
Do not add sand to clay. It gets recommended constantly and it's the advice that does the most damage, because a bit of sand through clay fills the gaps between the clay particles and gives you something much closer to concrete than to soil. You'd need to add sand at something like half the volume of the bed before it started behaving like a sandy loam, and at that point you've bought more sand than soil and you'd have been miles ahead building a raised bed instead.
When to stop amending and build up
If the bed sits at the low point of the block, or there's a hard layer under it you can't get through, no amount of compost is going to beat the water arriving from uphill. Build a raised bed, give it at least 300mm of depth, and fill it with good garden soil and compost so you're growing in something you chose rather than something you inherited. We cut treated pine sleepers to length at the saw bench, so the frame is the easy part.
Keep it mulched once it's planted, because a raised bed drains well by design and that cuts both ways in a dry summer.
Shop related products
- Naturally Good Garden Soil, 50L. For filling a raised bed rather than reusing the wet stuff.
- Brunnings Ultimate Dig It In Compost 30L. The one to work through heavy ground.
- Naturally Good Mushroom Compost 25L. Gentler, good for topping up between crops.
- Neutrog Whoflungdung Mulch 20kg. Goes on top once the bed is planted.
Did you know we also keep bagged gypsum in the shop and cut treated pine sleepers to length at the saw bench, and neither is on the website, so give us a ring on (08) 8536 4333 to check what's on the shelf.
The bagged soil and compost is in our garden centre, and if you want a second opinion on whether it's a clay problem or a water-arriving-from-uphill problem, come and describe the bed to us.
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I still reckon the bed at the bottom of the block is the one that teaches everybody this lesson.
Cheers,
Candeece
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