Don't Throw Out This Kitchen Leftover: Turn It Into A DIY Fertilizer Perfect For Carrot Seeds

Due in part to the tiny size of their seeds, carrots can be a bit tricky to sow and grow. Too many seeds that sprout in a small area result in overcrowded carrots that require thinning. They're best planted about 2 inches apart, but it can be tough to spread them out evenly when distributing a packet on its own. Meanwhile there's the problem of fertilizer: Too much nitrogen in the soil can make the carrots grow unattractive, hairlike rootlets. For this reason, some popular fertilizers should be avoided when planting carrots. Fortunately, there's a fix for both issues: Used coffee grounds.

One common hack for dispersing carrot seeds evenly is to mix them into dry, fine, washed sand in a shaker. The tiny seeds get evenly distributed in the sand, allowing for a better spread when sowing. And while there's nothing wrong with sand, the beauty of using coffee grounds is that you're adding a biodegradable component with some soil amendment properties, and repurposing kitchen waste all at the same time.

While coffee grounds have a nitrogen-rich blend of nutrients, spent grounds are only around 2.3 percent nitrogen, .06 percent phosphorus, and .6 percent potassium. When mixed into a potting soil or potting compost, spent coffee grounds can help nourish the soil surrounding your carrot seeds and carrots, without overpowering them with nitrogen. As the grounds break down, they act as a slow-release fertilizer. 

To make a fertilizer out of coffee grounds, first spread the spent grounds out on a baking sheet or tray and allow them to dry. Drying them as soon as possible reduces the chance for mold growth. If you have more than you need for this project, save it: Coffee grounds help many garden plants such as cabbage, basil, and tomatoes.

When the grounds are completely dry, grab a lidded jar and blend roughly ¼ teaspoon of carrot seeds to ½ cup of coffee grounds (believe it or not, that's a lot of carrot seeds). Shake well, then stir in four times as much potting mix as coffee grounds. Since you're growing carrots to eat, an organic, additive-free mixture is a good idea. Shake it all again. Carrot seeds need a lightweight mixture to germinate and grow, and this mix serves that purpose, since potting soil is lighter and looser than regular garden soil.

Make indentations about ½-inch deep in loose garden soil to create planting furrows. The handle end of a rake or trowel works well. Sprinkle the seed-and-potting-mix combo lightly into the impressions (it won't seem like enough, but it is), then water regularly, as recommended on the seed packet. For an even simpler way to spread the seed-and-soil mixture, instead of a jar, repurpose old salt and pepper shakers to sow seeds. Ideally, you'll end up with about 1 seed per inch, which gives the carrots room to grow. You will probably still need to thin some seedlings, but not nearly as many, and you shouldn't have any dense clusters of carrots coming up.