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QUESTION: Can you grow vegetables in just compost?

ANSWER: When you first consider growing vegetables in just compost, it may seem like a good idea. After all, compost is so rich and has so many nutrients that if a little is good, a lot seems like it would be even better. But the truth is that plants really need a particular balance of nutrients in their soil, and going above and beyond the amount they need can be detrimental to their growth. 

The nitrogen level of compost is much higher than that of regular garden soil, and high levels of nitrogen can actually be toxic for plants. The same issue occurs when it comes to micronutrients. A small amount of a substance such as boron will help boost plant growth, but if they get too much, it can be harmful. And if your compost is made with a large percentage of animal manure, it can contain more salt than plants can handle if they’re planted in compost alone. 

Growing plants in just compost can also cause issues with the soil’s ability to retain water. When it’s mixed with regular soil, compost improves drainage—in clay soils, which tend to be heavy, it loosens the soil to allow water to drain more freely, while when it’s mixed with sandy soil, compost improves the soil’s ability to retain water. However, used on its own, compost is just too loose to retain enough water. It drains much too quickly, and as a result, dries out too fast to foster healthy plant growth. 

Because compost is looser and lighter than regular garden soil, if you attempt to grow your plants in compost alone, you’re also going to encounter problems with soil stability. Due to its lightness, the compost doesn’t give the roots of plants the support they need to keep from toppling over.

On its own, compost will also settle dramatically and become more and more compacted as time goes on. This problem is especially obvious in containers, which will seem to be losing soil as the days wear on and the compost settles to the bottom.

Ideally, the soil in your garden should contain no more than five percent organic material, which is what compost is categorized as. For best results, spread one to three inches of compost on top of your existing soil before you begin planting, then work it into the soil underneath by mixing it in to a depth of six to 12 inches,

QUESTION: Can you fill a raised bed with just compost?

ANSWER: For the same reasons you wouldn’t grow vegetables in compost alone when they’re planted directly in the ground, you also shouldn’t fill a raised bed with just compost. The ideal percentage of organic material garden soil should contain is five percent, and your compost counts as organic material.

Using too much compost or attempting to grow plants in nothing but compost will cause problems for your plants when it comes to nutrition, soil stability, and the soil’s ability to retain water.

Just like human beings can overdose on the vitamins our bodies need to thrive, plants can also get too much of a good thing. Compost has high levels of nitrogen, which can be toxic to plants when the soil contains an excess amount of nitrogen.

Similar problems present themselves with micronutrients in the soil. For example, a small amount of boron will help plants grow healthy and strong, but too much boron will have negative effects for your plants. Compost also tends to contain much more salt than is healthy for plants, and growing plants in compost alone can cause them to be burned by the excess salts.

When it’s mixed into garden soil at the proper ratio, compost can work wonders for the soil’s ability to drain or retain water, whichever is needed. In heavy, clay soils, compost will loosen things up and aerate the soil to allow for better drainage. When compost is worked into sandy soil, it improves the soil’s water retention, keeping moisture available for plants. But on its own, compost is too loose to properly retain water, allowing it to drain right through and drying out much too quickly for growing healthy plants. 

The looseness of compost can cause another problem if you attempt to grow plants in compost alone: issues with soil stability. It just doesn’t have the presence and solidity that’s needed in order for the roots of plants to find purchase and stay upright.

Compost alone will leave plants unsupported and prone to falling over. Compost used on its own will also settle dramatically, compacting more and more as time passes. For plants growing in containers, this can be especially problematic as it will seem like the soil in the container is disappearing as time progresses.

For all these reasons, it’s best to stick with mixing compost into the soil you already have. An easy rule of thumb to remember is to spread one to three inches of compost over the top of your garden soil before you plant. Then work the compost down into the top six to 12 inches of soil.

QUESTION: Can you use cardboard for compost?

ANSWER: Despite what you may have heard, it is perfectly fine to compost cardboard trash—even if the cardboard is shiny because it’s covered with a gloss coating. When you do include cardboard in compost, though, there are a few things you need to know—there are troubleshooting (or rather, trouble preventing) steps that you’ll need to take to keep the cardboard from causing issues in your composting. 

Cardboard tends to be less effective at maintaining the appropriate moisture level  than the rest of the components that people use in compost. Shiny cardboard especially has trouble holding onto its hydration because the glossy top layer that’s responsible for its sheen functions as a barrier to keep water from ever being thoroughly absorbed. 

In other words, cardboard is out of equilibrium with the other elements of the compost heap when it comes to moisture level from the very start, from the moment when the water is first applied. To restore harmony, you’ll need to take matters into your own hands and help the cardboard along by wetting it down generously right before you throw it into the mix. 

Cardboard (especially when it has that slick top layer) is likely to take a while longer than most of your other composting ingredients to complete the process of decomposition and fully break down. This is an easy puzzle to solve, though. You can bring things into balance without a fuss, and do it efficiently, while you’re adding the cardboard to your compost pile, just by tearing any cardboard you include in your compost into small chunks so it will be broken down by the microbes in your compost more quickly.

Warning! Cardboard is extremely carbon rich, so you can’t add too much or it will bring the composting process almost to a complete stop. Use limited amounts and make sure you have plenty of nitrogen rich materials to balance it out.

Can I put hair in compost?

Human or pet hair works well in composting. As with everything else, if you put too much of a single ingredient in a compost pile or bin, it will take a very long time to decompose. So easy does it and not huge amounts.

QUESTION: Can I put egg cartons in my compost?

ANSWER: Many egg cartons are made of paperboard, so they’re perfectly fine to include in your compost pile. Use egg cartons in composting just as you would paper, and count them as part of your brown ratio because of the carbon they contain. One condition, however, is that you should make sure the egg cartons are dry and clean before you compost them. Of course, don’t add the ones made of styrofoam or other plastic materials!

If the carton is wet, that more than likely means an egg was cracked along the way somehwere and leaked onto the cardboard of the carton. You wouldn’t want to include an egg carton that had gotten messy with egg because, like meat, fish, grease, and other dairy products, eggs can cause both smells and pest problems when they’re used as part of the composting materials. For the same reason, if you place eggshells back in the spot they came from in the egg carton whenever you crack an egg, you should skip the eggshell cartons when you’re adding items to your compost bin. 

As a side note, you’d need to throw our hypothetical sloppy egg carton into the trash can instead of using the recycling bin. Many people don’t realize that food products or even just food residue should not be included when you’re separating your trash to send things to be recycled.) If you want to recycle substances that are tainted from coming into contact with food, like the cans from your vegetables, the guideline is to rinse out the material you’ll be recycling.

Make sure to clean things well so they are completely cleared of all food residue before you add the trash to your recycling bin. When it’s impossible to separate the food residue from whatever you’re throwing away, as is the case with greasy pizza boxes, for example, or our soiled egg cartons, you should throw the trash that’s been contaminated with food into the standard garbage can  instead of recycling it.