How to Reuse or Amend Old Potting Soil
Recently, I revitalized the pots from last year’s spring bulb display. As I was completing this task, it occurred to me that there might be some of you who wondered if it is okay to reuse potting soil? As it happens, the answer is emphatically ‘yes!’ and today I’ll share how I reuse and amend my old potting soil so your plants can continue to grow happy and healthy.
Would you believe that these bulb pots sat on my bench all year without any water or care? After all my daffodils and Spring bulbs bloomed last year, I simply left the plants to die back, and it wasn’t until this week that I decided to check and see if anything was sprouting again. Plus, I knew that the soil would be in desperate need of some nutrients before it could support another round of blooming plants. Rather than toss out and waste this old potting soil, I proceeded to amend it and reuse the potting soil for this new season.
There’s something magical about bulbs. Those brown, unsuspecting little packages hold so much floriferous power! Even as an experiences gardener, it was thrilling to rifle through each bulb container and see what bulbs were sprouting and coming back again. In fact, if you’re curious what types of bulbs you can plant now, head on over to my YouTube Fall Planting Extravaganza to see what I planted this year.
About Potting Soil
Potting soil is different. It is specifically created to stay fluffy, un-compacted, and drain well. Because of these specific characteristics, many mixes have additions like perlite, rice hulls, and peat moss that don’t really provide nutrients, but are necessary for texture. Therefore, when you go to reuse potting soil, you might find that some ingredients (like perlite for example) don’t decompose, so you don’t need to add anything to create a lighter texture! On the other hand, ingredients like compost or manure will have decomposed and the nutrients will have been used up from that season or washed out from rain. This is why I tend to amend old potting soil with compost or worm castings—-things that are nutrient rich—-but don’t necessarily add new drainage or aeration components.
Over time, if you do notice your old potting soil starting to get super compacted and not draining well, you might want to consider adding some perlite, rice hulls, pumice, or even just grab another bag of potting soil to keep the proper texture for your container-grown plants.
When Should I Not Reuse Potting Soil?
Before we go on, there are some instances where it would not be wise to reuse your old potting soil. For example, if the plants succumbed to disease or a soil pest that you do not want to have in your garden anymore, I’d get rid of the soil. Admittedly, you could attempt to sanitize the soil through solarization—essentially using extremely high temperatures from sun exposure to eradicate soilborne pests—if you really are opposed to disposing of your old potting soil. I mention solarization because it is a non-chemical means to eradicating soil pests, and it would most likely be the route I would take in my own garden. For a rundown on how to use solarization in the home garden, check out this resource by UCANR that shows the step by step process. Although they don’t specifically address containers and potting soil, these same principles could be applied to container soil on a smaller level. Just some food for thought….
Supplies Needed to Amend or Reuse Potting Soil
My go-to amendments for adding to old potting soil are as follows:
Targeted, Organic Fertilizer *optional
Worm castings *optional
When I say “targeted” organic fertilizer, I am referring to using a fertilizer specifically made for whatever you plan on adding to your pot or container. For example, this week I potted up my daffodil bulbs, and so I used a flower and bulb fertilizer to amend the old potting soil.
In many ways, I treat my pots and containers the same way I treat all of my garden soil. If you haven’t yet read about how I amend my raised bed and garden soil organically, you can read about my process HERE.
How to Amend Old Pots & Containers
When you’re ready to refresh an old pot or container, you have a few options. First, you could choose to simply top with compost and slightly mix it into the soil below. This scenario is best for large grow bags that you might treat more like a raised bed. For instance, if the container is so large that the volume of soil is a lot like a raised garden bed you could simply top with compost— mixing it gently into the top layer and then transplant.
A second option for reusing old potting soil and refreshing a container is to empty out the whole thing and remix the soil. This is my preferred method. Also, this is the option I used for my potted Spring bulbs because I hadn’t watered them in so long that the entire pot was super dried out and I could tell that the soil wasn’t super healthy and teeming with life. In this case, it would take a long time for the compost to get mixed in, and the whole container might even be slightly hydrophobic (aka reluctant to absorb water) so it’s best to just recreate a soil mixture for those pots.
To reuse this potting soil, I simply dumped out the contents and added compost and some organic flower and bulb fertilizer before refilling my container. In regards to how much compost, I usually eyeball it, but approximately a ratio of 1 part compost to 3 parts potting soil will work just fine. Additionally, if you want to sprinkle worm castings into the mix as well, go for it!
Can I Add Old Potting Soil to My Garden?
Lastly, this is one question I get a lot as well. As long as your potting soil was healthy, feel free to just dump it in your raised bed or garden instead of reusing the old potting soil. This does not mean you are amending your soil, but simply that it won’t harm your garden. In raised beds specifically, you will find that the drainage/aeration components of potting soil will also help with your raised bed soil. But don’t forget, you’ll still need to amend your raised beds and garden per usual!
Even though I have raised beds and in-ground garden areas, I love growing in containers and pots. Container gardening allows us to truly control soil health and composition, while also helping gardeners everywhere maximize space! In some instances, like my blueberries, container gardening gives me the edge on creating an acidic soil environment for the most success. Even though certain aspects (like watering and amending soil) can take some trial and error in containers, I hope you find this information helpful! Thanks for reading!
If you’re curious what the garden looks like here in December, please join me for a quick tour over on YouTube.