Leave the roots of annual flowers with small roots in the ground as they will break down quickly and add organic matter to the soil. The roots of legumes like peas and beans can also be left in the ground as the nitrogen formed on nodules will be released into the soil. Remove roots of tomatoes and potatoes to avoid the spread of disease to other plants.
Leaving annual plant roots in the ground
Trimming to the tops off annual flowers and leaving the roots in the ground can be a great way to clean up your garden area without disturbing the root zones of other plants.
If you have planted annual flowers near citrus trees, trim them off at ground level at the end of the growing season. This will avoid disturbing the small feeder roots that grow near the surface of the soil.
What happens when plant roots are left in the ground
If plant roots have their stems removed, they will eventually break down in the soil. Thin, small root systems of annual plants will break down quickly. The root systems of Viola, Marigold and Dianthus will all break down in the soil at the end of the season.
Cover the root areas with cardboard, newspaper and mulch to encourage the root system to break down in the ground. Soil bacteria will incorporate the root system into the soil.
Removing tree roots from the soil
Many trees will re-sprout if the roots are left in the ground. This can include pine trees, citrus, and eucalyptus. These plants can re-sprout from stumps and grow new stems.
Tree roots can be left in the ground if you continue to remove new stems from the stump until the plant runs out of nutrients and it will eventually stop growing. The root system will rot away over time.
Citrus roots can grow back rapidly as they are often grafted onto fast growing root systems. The stems that sprout will not usually produce fruit as they will come from the root stock rather than the grafted stem.
When to remove roots from the ground
If you are planning to grow something else in the same spot as the plant you are removing it is best to remove the roots. This will allow you to loosen the soil structure, mix in some new compost and prepare the space for the new plant.
Grass roots with runners
Any grasses that have runners should be removed completely including the roots. Buffalo and Couch grass have long roots that can re-sprout easily. If you are removing large areas of lawn, dig down and remove the roots at the same time.
Grass can be killed off first by covering it with black plastic. Roots can still survive this process so dig them out before planting something else in the same spot.
Deep rooted weeds
Weeds with deep central root systems like thistles are best removed completely. The central root systems can re-sprout if left in the ground so dig them out with a weed remover.
Plants with diseases
Any plants or weeds with diseases should be removed completely including the roots. This will help to avoid reinfecting any new plants grown in the same place.
Leaving vegetable roots in the ground
Peas and beans
Leave pea and bean roots in the ground as they trap nitrogen in nodules formed on their roots. Soil bacteria will break down these nodules to make the nitrogen available to your next plants.
Remove tomato plants and their root systems to reduce the risk of diseases from staying in the soil and infecting other plants. Tomato roots can keep pests such as nematodes on their roots in the soil.
Broccoli, cauliflower and cabbage
Brassica root systems like broccoli, cauliflower and cabbage can grow large so they are best removed and placed in your compost bin instead. Although these roots won’t cause problems they are likely to get in the way when you plant your summer crops.
Remove all of your potatoes including the roots when they are ready to harvest. Potatoes left in the ground can re-sprout the next year. Rotate the crop location to avoid any pests or diseases living in the soil.
Herb roots like rosemary, basil, parsley, chives and coriander can be left in the ground. These roots are not invasive and will break down. Trim the plant down to the ground level and cover it with mulch to make it break down quicker.
Mint roots should be removed completely if you are planning to move the plant. Any root systems left in the ground can re-sprout from nodes and re-grow.
Leaving plant roots in pots
If you are removing a plant from a pot and want to re-use the soil it is best to remove the roots. The root system will make it difficult for the new plant to grow a healthy root system as the old roots are in the way.
Roots in pots will not break down quickly like those in the soil. They are not in contact with ground soil which is rich with microorganisms that break down organic matter. Roots in pots will break down over time but it can take much longer.
Top ways to deal with plant roots
Turn root systems into compost tea
Leave old roots from plants in a bucket of water and cover it with a lid. After 1-2 weeks, the nutrients and excess soil will be released into the water and it can be added to your garden. Dilute it in 1:4 parts water and add extra seaweed solution for a great root tonic.
Leave roots in the ground
Leave root systems of small, annual plants and legumes. These will breakdown quickly and add extra organic matter to your soil.
Add roots to your compost
Root systems will break down quicky in your compost. Shake off excess soil and chop them into smaller pieces. Mix them through the other compost ingredients and water them in well.
Leaving old plant roots in the ground – Summary
Leave the root systems of small annual flowers, peas, and herbs in the ground to avoid disturbing the soil and add extra nitrogen. Soil microbes will break down thin roots turning them into humus and enriching the soil with organic matter.
Remove tree roots to avoid them from growing back or trim off shoots that return and the root system will eventually stop growing.