You are currently viewing Is Compost Free Draining?

Is Compost Free Draining?

You may have noticed the soil in your flower beds becoming either too dry or waterlogged – and the solution may be to add in some ‘free draining’ compost.

Compost is free draining in that when it’s added to different soil types it helps to retain or drain water, keeping moisture levels regulated and optimum. So when your soil becomes too dry, compost can help lock in more water – and when your soil is boggy it can help water flow through it.

Let’s look at why the free draining characteristics of compost are important, how to get the mix right in your soil – and also discover some alternative materials to aid water retention and drainage in soil.

What is Free Draining Compost? (Also Called Well Draining)

Roots, oddly enough, can be too wet. In fact, overwatering is a real problem. Experts say that overwatering is the biggest issue in gardening and landscaping today.

The tricky thing is that plants that are overwatered look like they need more watering. Overwatered plants get brown, yellowed and wilty. The leaves fall off. But they don’t need more watering – they need more effective watering.

Compost is a great way to nurture root health. Compost provides a wonderfully diverse range of nutrients and microorganisms that promote roots and soils. The addition of compost helps clay-rich soils retain moisture and breaks up their hardness. Sandy soil doesn’t get hard, but water runs right through. Compost helps.

When you don’t have clay-rich or sandy soils, compost’s moisture-hoarding tendencies can be a problem. Too much compost in an already moisture-rich soil can turn your garden into a dark brown, soggy, mucky bog. Just when you think you are boosting plant health with black gold (compost), turns out you are actually drowning your plants.

Not to fear. Not all composts are created equal. There’s a solution – free draining, or well draining, compost. You can buy it, or you can make it.

Why is Having Free Draining Compost Important?

Plants grow everywhere, right? So how hard can it be?

Plants need nutrients, water and air. Plants growing in the wild are good at getting the mix they need to thrive. Humans planting plants in gardens and pots often get the mix wrong because not all plants have the same needs.

Most plants benefit from a soil that is half air space, almost half solid minerals and no more than 5% organic matter. 

Plants need oxygen. In soil, oxygen hangs out in the gaps between soil clumps, in between rocks or around root clusters. When you water, the water fills the gaps. When that water doesn’t drain, plants don’t get the oxygen they need, and they suffocate and die.

The age-old gardening challenge is getting the right mix for the right plants. Plants, and their roots, have different needs – some like moisture and some don’t. The solution is to mix up a soil that your plants can thrive in.

How To Improve Free Draining in Pots & Planters

If your flowerpots are getting soggy because water just hangs around, it’s easy – start over. Repot with a better potting soil mix.

Here’s a simple drainage test: water your pot thoroughly and start a timer. You should see water coming out the drain hole in one to two minutes.

Speaking of drain holes, if your perfectly coordinated, can’t-live-without-it pot doesn’t have one – get one!

If your pots fail the drainage test by draining too slowly, then repot your plant using more free draining ingredients, like mulch, perlite, vermiculite or sand. Here’s a link to potting soil recipes for different potted plants.

In the past, experts recommended adding rocks to the bottom of a pot to improve drainage. Not so anymore. Now, they recommend getting the potting soil mix right and putting a paper coffee filter on the bottom of the pot. The coffee filter, or a small piece of screening, will keep the soil from running out of the hole.

How To Improve Free Draining in Flower Beds

If you are just starting your flower bed adventure, then consider designing your beds and soil for good drainage. If you already have garden beds – there’s still hope. Read on.

Here’s a drainage test for flower beds: dig a hole a foot deep and a foot wide. Fill it with water and let it drain away. Fill it again and start timing. For soils with good drainage, the hole will empty in 10 minutes or so. A healthy rate is about an inch an hour. If your hole is still watery in an hour, you have poor drainage.

If you are starting a new flower bed, use a free draining mix. A good mix for most flower beds is: 40% garden soil, 30% peat moss (or 10 to 20% sand), and 25% compost. The remaining 5%, should be nutrients like bone mean, Neem powder or mycorrhizae powder.

When designing your beds, consider raised beds. Raising your flower beds helps improve drainage (your back can thank me later). 

Let’s say you already have flower beds and your drainage just needs a small nudge- try a tool called a broadfork on your planted beds. 

If your garden needs significant drainage improvement, try sheet composting, also called lasagna gardening. Lasagna gardening fights weeds and boosts flower bed health. Not to mention – one of the “lasagna” layers is newspaper or cardboard, so you are recycling too! Bam! Check it out.

Here’s a counter-intuitive drainage hack: don’t pull up your annuals or vegetables by the roots in the fall. Cut them off at soil level. The roots you’ve left will decompose and leave tiny water highways.

An old farmer’s hack is using a cover crop for a season. Cover crops (aka green manure), have deep, straight roots that are ideal for helping with drainage. Simply till them under in the fall and plant your favorite flowers next season. You may be thinking that cover crops are boring and ugly – but you’d be wrong. Check out this list.

Try to make adding free draining compost to your garden beds a yearly ritual.

Free draining compost

What Else Can You Mix With Poor Draining Soil To Improve Drainage?

There are many ways to amend gardening soil. Some are available in stores and some you can find in your own yard. 

When you are trimming bushes in the fall, keep the twigs and canes. Then, cut them into one-inch pieces and add the pieces to soil. Pea gravel makes a great non-organic but natural mulch. 

Keep the sawdust from building projects and add it to your garden soil. Or add: cocopeat, worm castings, straw, manure, kelp meal, cornmeal, or grass clippings.

The list below contains the most common soil amendments.


Mulch is a gardening catch-all term for many materials. Inorganic mulch, like pea gravel or pebbles, can be good in soil and they don’t decompose. Organic mulch can be made from bark, leaves, straw, newspaper, or pine needles. Mulch improves drainage and also adds bulk that helps plants access oxygen.

Organic mulch decomposes, so you will have to add more every season.


Sand goes well in clayey soil to provide some natural drainage. Look for sandbox, construction or river sand. Be careful that the sand you pick is not too fine, as it will become concrete. Also, no beach sand – it has too much salt. 

Generally, only 10% to 20% sand in gardening soil will increase drainage to healthy levels. Don’t use too much sand unless you are planting succulents. Too much sand will result in too much drainage.


Perlite comes from weathered volcanic glass – also called volcanic popcorn. Perlite is very porous, so it’s great for providing oxygen to those roots. 

Perlite is very soft and crumbly and will compact to powder if you mix it with heavier stuff. Or if you mix it too hard – you just get perlite dust.


Vermiculite holds lots of moisture, has a natural pH and contains some nutrients. Vermiculite will not mold and is light enough to be a good option for seeding. 

For seed starting, use the smallest vermiculite with peat moss or cocopeat. For garden beds or large pots, use a larger vermiculite, blended in one part vermiculite to every three parts soil.

Final Thoughts

Ultimately, the free draining properties of compost will help regulate the moisture levels in your soil by locking in more water when it’s parched, and aiding drainage when your soil is waterlogged.

Both soil scenarios are potentially damaging for your plants and flowers – so using compost (or one of the other soil additives mentioned), will help you grow healthy plants in healthy soil. 🙂

Mark H.

Homeowner and property investor Mark H. aspires to bring you the very best outdoor living content, based on his years of experience managing outside spaces. Read more >