You’re finally realizing that your favorite garden bed, one you’ve been tending for years, is really not doing as well as it used to. It could be that the soil in there is just getting old and not able to support plants the way it used to.
When Is Soil Considered Old?
This is a bit of a tough question to be specific about age when it comes to garden soil. The problem isn’t really a matter of how much time has passed, but rather how much has been growing in that spot without any new fertilizers added. In other words, age doesn’t matter as much as nutrient content.
Soil that has been growing heavy feeding plants for many years without any amendments is going to be exhausted. Things like fruiting vegetables (such as tomatoes or eggplant) or flowers that produce a lot of blooms. Petunias and roses are known to be heavy feeders.
How to Tell When Your Soil Is Depleted
Since we’re really talking about minerals and nutrients rather than age, it can be hard to figure out where your garden soil is at. At least not when you are just looking at it.
The first signs would be that your plants are not doing as well as they should be, and that it’s been years since you’ve done anything to improve the soil. Once you see there may be a problem, it’s time for a little more investigating.
If you are worried about the nutrient content of your soil, it’s time to get a good test kit, like this digital one, and see what you’re dealing with. They’re not complicated and you won’t need a degree in chemistry to understand them. Everything is conveniently color-coded.
Some kits are targeted for just one nutrient (usually nitrogen) but for this purpose, it would be smarter to get a larger product that lets you test for more compounds because you want to see the full spectrum of your soil’s contents.
Look for nitrogen, potassium, phosphorus, calcium, and magnesium. Check the pH (acidity) levels while you are at it. Relatively neutral is best, which is a pH of 7. When it gets lower, the soil is becoming acidic.
Obviously, you can just follow the directions in the kit, but here is a quick description of how these tests work. For each sample, you’ll need a few tablespoons of soil and some distilled water. In the provided container, mix the soil with water and let it sit.
When the dirt settles, add the testing reagent and see what color the water turns. There will be a chart to compare your samples with. This can tell you which of the common nutrients you are lacking.
Some kits may use a paper dip-strip instead. The overall principle is the same. You would just dip the tester in the soil water, and see what color it turns.
Ideas for Your Old Garden Soil
1 – Revive with Fertilizers
The best thing to do with old garden soil is to perk it back up with an infusion of fresh organic material and nutrients.
Basically, you have two choices when adding fertilizers to tired garden soil. Standard processed products that come in liquid or granular form, which have a specific quantity and blend of nutrients in them. You measure them out, dilute in a certain amount of water and apply to the garden.
These products will probably have 3 numbers on the package, known as NPK numbers. That stands for nitrogen, phosphorus, and potassium.
The other choices is to use more natural materials, though they are not going to be as precise. Two classic and very effective natural fertilizers are compost and animal manure. Both will add a lot of organic material as well as a whole spectrum of nutrients.
Just remember that any manure (other than chicken) needs to be aged for at least 4 months before you use it. Otherwise, it will be too high in nitrogen and will easily kill your plants.
If you need to target specific compounds that are lacking, you can try these materials:
- blood meal – nitrogen
- bone meal – calcium, nitrogen
- seaweed emulsions – potassium
- potash – potassium, raise pH
- alfalfa – nitrogen
- lime – calcium
- Epsom salts – magnesium
- used coffee grounds – nitrogen
- fish emulsions – nitrogen, phosphorus, potassium
After you take your sol tests and see what you need, any of these products can be found at a typical garden or landscaping store.
2 – Recycle as Potting Soil
Though houseplants do need nutrients in their soil as well, it’s a little easier to manage a small dose of fertilizer when dealing with potted plants indoors. So taking your old garden soil inside can be one option, as long as you sterilize it first.
Even tired dirt can hold plenty of pathogens or insect eggs. No sense bringing that into the house. You can sterilize old garden soil in the oven, and its very easy to do.
Take a few shovelfuls of earth, and pick out any large rocks or sticks. Add a little water so that it’s damp. Spread it out about 3 inches deep in a baking pan and cover up with aluminum foil. Poke a hole in the foil and stick an oven-safe thermometer in, making sure that the sensor is right in the dirt.
Set the oven to 180 F but don’t start the timer until the actual dirt is registering at that temperature. Keep it at that heat for half an hour, and then remove from the oven to cool on its own.
Now you can use your old garden soil in the house more safely. It is still going to be low in nutrients, but a houseplant fertilizer can take care of that.
3 – Change Plants
If you really aren’t inclined to do a lot of work, you can also just change up what you are growing in that area. Plants that can do well in poor soil would be many kinds of creeping ground cover plants like bugleweed or sedum, and larger vines like Virginia creeper can do well in your old spot as well.
Bleeding heart and some geraniums will also give you some flowering options too. Or you can go all the way and move the garden bed entirely, and use the area of old soil for a new water feature or a lovely outdoor sculpture.
Growing up with a mom who filled her home (inside and out) with all sorts of plants, Lisa got her start in gardening at a young age. Living now on her own with a home and yard full of plants (including an indoor greenhouse), she shares all the gardening tips she’s gained over the years.
Wednesday 21st of August 2019
" Just remember that any manure (other than chicken) needs to be aged for at least 4 months before you use it. Otherwise, it will be too high in nitrogen and will easily kill your plants."
Actually, chicken manure is the WORST. It must be composted, or made into "manure tea" (basically, a little chicken manure in a whole lot of water; search online for instructions). Cow manure doesn't actually need to be composted to avoid burning plants; rather, it's to kill off grass seeds. Same with horse manure. Rabbit manure, on the other hand, can be used as is--even instead of soil--because it's been digested twice (yup; look it up if you don't believe me).
Lisa | The Practical Planter
Friday 23rd of August 2019
Thank you for the useful information! I’ll definitely do some more research on that.