Old mulch does not need to be removed before you top your garden beds up with new mulch. Old mulch is a fantastic addition to your soil slowly breaking down to add extra organic matter to the soil. Feeding worms and soil bacteria and helping the soil to hold water.
Here are the top things to know about removing old mulch and the benefits of leaving it on the soil.
Best reasons not to remove old mulch
Leaving old mulch on top of the soil has many benefits for your plants and soil so check out my top 5 reasons to set and forget mulch.
Old mulch breaks down into humus
Old mulch is the beginnings of compost and if left on top of your soil will break down to a rich amazing humus. Humus is a fantastic soil component which is made up of the organic matter from mulch that has been broken down anaerobically.
Soil bacteria breaks down the mulch and worms come to eat the bacteria and organic material. Leave old mulch and top up with new mulch to get the benefits of humus.
Old mulch improves the soil
Compost and humus hold water, add nutrients to the soil and improve the organic matter levels of your soil. Over a number of months and years, humus will improve your soil and you will grow bigger and healthier plants.
For more on the difference between humus and compost, check out my article here: Difference Between Humus and Compost | Top 5 Key Differences.
Old mulch feeds worms
Old mulch will break down over time by soil bacteria which is one of the favorite foods of worms. The cycle of soil bacteria coming to break down old mulch and then worms coming to eat the soil bacteria breaks down and releases nutrients from the mulch.
The nutrients released are then made available for plants which helps them to grow larger, stronger with more leaves and strong stems. Nutrients include nitrogen, potassium and phosphorus and minerals such as calcium.
Old mulch keeps water in the soil
The soil under old mulch will hold more soil for your plants meaning that you will need to water less often. The mulch will form a blanket which reduces water evaporation but will also have the benefit of adding humus to the soil over time which adds to the water holding capacity.
Leaving old mulch avoids plant root damage
Leaving old mulch on the soil will avoid any root damage that might happen if you attempt to rake mulch away from the surface. Some plants, including citrus trees have delicate feeder roots near the surface of the soil which are easily damaged with rakes or shovels when you try to remove mulch.
Leaving old mulch on top of the soil and topping up with new mulch is the easiest option and you can make sure that you don’t accidently damage plant roots.
Removing old mulch from vegetable gardens
Vegetable gardens will benefit from leaving old mulch on the soil and mixing it in to build it up for your next growing season. Removing old mulch can be a waste as at the end of the growing season, either summer or winter you will be left with some old, partly broken down mulch.
Old mulch should be ¾ of the way to turning into compost and digging it into the soil and waiting 2-4 weeks can be an easy way to finish the composting process.
To achieve the best results, dig light mulches like straw, hay or sugar cane mulch through the soil when your vegetables have finished for the season. Remove old plants like tomatoes and dig the old mulch through the soil.
If you have used bark mulch around your vegetables it is likely that this will not have broken down completely by the end of the season. You can remove vegetables that have finished growing and instead of digging the mulch through the soil, leave it on the soil and plant straight into the soil instead.
Removing old mulch from flower beds
Flower beds that have been mulched with bark mulch are perfectly fine if you leave the old mulch on the surface and top up with new mulch. Bring the mulch level back up to 2-3 inches to keep soil moisture in while still allowing the rain to penetrate through to the soil.
The bottom layers of mulch will break down into the soil and the top, fresh mulch layers will help to prevent weeds and disperse large amounts of rain.
Removing old mulch from around trees
Old mulch that has been placed too close to large tree trunks can be raked back and removed from the trunk area. Use a rake to expose the trunk and leave a larger gap, up to 3-5 inches to avoid mulch falling back and sitting against the tree trunk.
The best mulch for established trees is a tree or bark mulch which will help to keep water in, protect the roots and improve soil.
For more on how to mulch mature trees, check out my previous article here.
Removing old mulch from herbs
Mediterranean herbs will benefit from a top up of bark mulch every 3-6 months rather than removing any old mulch. Rosemary, thyme, oregano and marjoram all benefit from bark mulch which will break down over time and keep these perennial herbs growing strong.
When old mulch should be removed
The time where old mulch should be removed is when the layers have built up to be above 3 inches thick. Mulch that has been laid too thick can grow mold or fungus and can stop water from reaching the soil.
For mulch layers that are thicker than 3 inches, remove some gently with a rake and place the mulch in another are in your garden or add it to your compost bin to break down.
What to do with old mulch
Excess old mulch that has been left in a pile or has built up to thick on your garden beds can be reused in some fantastic organic ways including composting, adding them to a worm farm or making compost tea. Check out these great ways below.
Compost
Old mulch can be added to compost bins to break down over time. Old mulch will already be partly broken down so will need a shorter time to break down and will quickly break down and be ready to be dug into your soil.
Wait until the mulch breaks down resembling a dark soil before digging it into your garden beds.
Check out my previous article here for more on how to add mulch to a compost bin.
Worm farm
Old mulch can be added to the top of your worm farm and works as the perfect worm bedding. Add old mulch including straw, bark chips or sugar cane on the bottom layer to set up your worm farm or as a top up to cover food scraps and deter ants.
Make mulch tea
Mulch can be left in a bucket of water with a lid to break down and make mulch tea. Use a 4 gallon bucket and add 4-5 handfuls of mulch. This can be added into an old pillow case to allow the nutrients to release into the water.
The mulch tea can then be added onto your garden beds as a gentle fertilizer and soil conditioner.
Old Mulch FAQ’s
Add new mulch on top of old when the level gets below 2-3 inches thick. Mulch layers less than this will not stop weeds from growing through. Top up the mulch to this level which will likely need to occur every 3-6 months for bark mulch and every 2-3 months for straw, hay or sugar cane mulch.
There is no need to replace mulch, instead top this up with new mulch to reach a 2-3 inch level to protect your soil. Only replace mulch if you feel like you want a fresh look, which might be a great idea if you are selling your house. It is worth noting however a thin layer of new mulch can hide old mulch colors easily and save you time.
You should mulch all soil that is exposed. Mulch as soon as you have planted, after rain, after planting flowers, vegetables and herbs and when you have planted a new tree. Always cover the soil with mulch to prevent weeds and build up the organic matter slowly.
Do not till new mulch into soil or bark mulch that still resembles pieces. Old straw or sugar cane mulch that has turned brown can be dug into the soil and left to finish the break down process before planting. Old mulch that is still in large pieces will take nitrogen from the soil and your plants and can slow their growth or kill them.
The best time to mulch is after rain, after planting and before fertilizing. Cover vegetable gardens with straw mulch, add bark mulch under citrus and large trees as well as flower garden beds. If you can see heavy rain in the near forecast, wait for the rain and then mulch afterwards.
Should I remove old mulch? – Summary
There is no need to remove old mulch unless it has built up beyond 3 inches thick. Old mulch is part way to turning into compost, the best addition to your garden soil. Save yourself time and money by topping up old mulch with new instead of removing it.
Happy mulching.
I am an accredited practicing dietitian, experienced gardener and a dedicated cook. I love writing and sharing my experience so you can learn from my successes and mistakes.