It is possible to add too much compost to your garden which can increase the phosphorus and potassium levels, dry out the soil or even cause reabsorption of nitrogen if the compost is not completely broken down.
You can fix your soil if you have added to much compost and get your garden producing well in a short time.
Problems caused by too much compost in your garden
There are some problems that can be caused by too much compost in your garden. Here are the top problems that can be caused by adding too much compost to your garden.
1. The soil is too dry
Strangely enough while some compost is great for water absorption, I have found that too much compost can actually have the opposite effect. The compost will not hold as much water as mix with a higher soil content as soil contains clay particles which hold the water.
You may notice that if you top dress with compost it can dry out quickly. The combination of soil and compost will hold water well but too much compost without soil can dry out.
2. Phosphorus and potassium
The addition of too much compost can affect the nutrient levels in the soil. Compost contains higher amounts of phosphorus and potassium than normal soil levels which can be too much for some plants including root vegetables.
3. Weak plant roots
The addition of too much compost can cause plant roots to become weak. As the soil will be very soft and higher in nitrogen, the grow growth can be affected and the plant may not be held as solidly in the ground.
Larger vegetables like broccoli and cauliflower need a strong root system to hold up the heavy heads. Too much compost can cause them too fall over.
4. Problems with unfinished compost
Another problem with too much compost can occur if the compost is not completely broken down. As the compost continues to break down it will temporarily reabsorb some nitrogen taking it away from plant roots.
Soil bacteria move in to break down the organic matter in the compost and will break it down and will slowly re-release nitrogen in the soil for the plants. In the short term however nitrogen levels decrease.
How much is too much compost?
Mixing through more than 50% of your soil content with compost can be too much. As a general rule adding up to 30% compost to your soil will add a good amount of nutrients and help the soil to hold water.
Make sure the compost is fully broken down, looks dark and similar to soft soil. This is the perfect ingredient for your vegetable garden, flower beds or as a top dressing for citrus trees.
Top dressing with compost
Another great way to add compost to any established plants including large trees, shrubs, fruit trees and vegetables is the process of top dressing.
Using a rake, move the mulch back from the soil. Add around a 2-3 inch layer of compost on top of the root zone of the plants taking care not to disturb the soil and damage any surface roots.
Cover the compost with a 2 inch layer of mulch to keep it moist and avoid any weed growth.
Top ways to fix too much compost in your garden
If you have added a lot of compost to your garden and feel like there might be too much there are 3 easy steps to help to fix your soil.
1. Let the garden rest
The first step is to let your garden rest. This will give your compost time to break down, for the soil bacteria and worms to move in and start to bring back the balance of nutrients.
You can dig the soil over and even add some garden soil from another are of your garden. Mix this all through and allow the garden to sit for around 4 weeks. Water it in well and leave the garden to rest well.
2. Add a green manure crop
To protect your vegetable garden soil you can grow a green manure crop over the top. The simplest crop to crow is mustard. These seeds grow very reliably are larger and easy to deal with. You can even take mustard seeds from your cupboard and plant them across your soil.
Wait for around 3-4 weeks for the crop to cover the top of the soil and then dig it through. This will help to balance the soil nutrients and even add back some nitrogen. Let them break down in the soil for 2 weeks before planting anything else.
3. Mulch the soil
Adding mulch on top of the soil is the best way to protect the soil while you let it break down, settle and naturally incorporate the compost. For vegetable gardens, add a 2-3 inch layer of straw or sugar cane mulch to the top to protect the soil from drying out.
Top tips for adding compost to your garden
It is very difficult to add too much compost to your garden as it breaks down quickly and will naturally mix through your garden soil. If you are adding up to 30% of the soil content with compost once per year will not be too much for your garden.
- Add a small amount of compost in spring and fall
- Mix through the compost thoroughly with a garden fork
- Cover the compost with mulch, even if you are not ready to plant yet
- Add completely broken down compost
- Add small amounts of aged manures to your soil, this will add extra nitrogen
How to fix too much compost in your garden | Summary
If you have added too much compost to your garden it can make the soil dry, unbalanced and it may not grow the healthy vegetables you would expect. You can fix the balance by adding some soil from another area of your garden and planting a green manure crop over the top. Let your soil rest and in 4 weeks it will have settled and soil bacteria will have started to incorporate the compost.
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.