Written by Dale Richardson - Updated: June 23, 2023
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It's always great to reuse glass jars, and they make an ideal container to grow carrots. Growing carrots in a jar lets you see your carrots grow, and it is a great way to grow a few carrots inside in a small space. Here's how to grow carrots in a jar successfully.
To grow carrots in a jar, choose a jar that is deep enough for the roots with a wide opening, such as a wide mouth mason jar. Put a layer of rocks in the bottom for drainage, and fill with soil. Plant 2 to 3 seeds in the jar according to the packet instructions. Keep them watered well until harvest.
Glass jars make very good pots for carrots. Since they are quite small and do not have drainage holes, however, there are a few things to consider. It also makes a great project to do with children.
It is important to choose a jar that is the right size and shape to properly grow carrots. You want a fairly tall jar to accommodate the long taproot, and a wide opening is ideal to allow space so the carrots do not crowd each other. A 1L wide-mouth mason jar is ideal for most varieties of carrots.
However, You can also use any jar you have on hand. Empty spaghetti sauce jars are a good size, as are any tall jars that are around 18cm to 20cm (7inches) tall for most carrot varieties. You can use a shorter jar if you plan on growing a shorter variety carrot, or if you want to harvest them as mini carrots.
Read Next: How to grow carrots in a greenhouse.
Most traditional planters or pots have drainage holes to allow excess water to drain away. This is important to keep seeds or plants from becoming waterlogged and rotting out. Glass jars do not have this (obviously!) so creating a space for the water to drain is important. This drainage space can be created by putting a layer of rocks or gravel in the bottom of the jar. The water will drain from the soil and into the rock layer, keeping the soil from becoming saturated if it is watered too heavily.
Image by Carmen Edenhofer
You want to put in enough rocks to provide adequate drainage, but not too much to take away valuable growing space for the tubers. 2cm to 4cm (3/4-1 1/2 inches) is usually sufficient for a 1L mason jar.
Any size of rock will work, but keep in mind that smaller rocks will create a more solid bed for the soil to rest on. With larger rocks, more soil will be washed through to the bottom of the jar when the plants are watered.
It is not recommended to drill your own drainage holes in the bottom of the jar. While it can be done, it is a fairly difficult and involved process. The jars often break or shatter, and can cause serious injury in the process. Besides, the point of using glass jars is so you have a ready-to-go growing container without creating a make-work project. If you want an upcycled growing container with drain holes, cutting holes in an empty yogurt container would be a good choice.
Now you can fill the jar with your desired planting medium. You can use purchased potting soil, make your own potting mix, or use soil straight from your own garden.
Carrots do not grow well in heavy or compacted soil. So if you do use soil from your own garden, make sure it is quite light and no too much clay. Mixing in a handful of compost will create a good texture while also feeding the carrots as they grow.
Whichever planting medium you use, moisten the soil before putting it in the jar. This will ensure all of the soil starts off at a good moisture level to facilitate an ideal germination environment. The easiest way to do this is to put your soil in a bowl and slowly mix in water until the mixture is damp but still crumbly. You should be able to form it into a ball in your hand, but it should not be sticky.
Do not pack the soil in too tight, but just lightly press it down to make sure there are no air pockets that could sink later on. Leave about a 2.5cm (1inch) space at the top of the jar. This will allow you to water your carrots without having the water spill over the top.
Plant 3 to 4 seeds in each jar. Carrot seeds are extremely small, so it is tricky to only plant a few seeds. However, most jars are only big enough to grow 2 or 3 carrots to maturity, so you don't want to put in too many seeds. Plant the seeds according to the instructions on the seed package.
Why put in 4 seeds when the jar only has space to grow 2? You generally want to plant more because most carrot seeds only have a 60% germination rate. This means that only 60 percent of the seeds you plant will actually grow. If you only plant 2 seeds, there is a good chance only one (or sometimes) none will grow, and you will be wasting valuable space by growing an empty jar.
Image by Carmen Edenhofer
When growing in a glass jar, it is very important how you water your carrots. Even with the drainage rocks, the soil can quickly become saturated if you apply too much water at a time. Lightly mist the top of the jar every day will often be enough to maintain a good growing environment. The nice thing about growing in a glass jar is that it allows you to see what is going on below the surface. If you see that the soil in the jar is drying out, add enough water to keep it damp.
Carrots in the field grow best when they receive 1 inch of water a week. However, this is a measurement of how much water falls on a given area in a certain time frame. This does not really apply to container gardening, since a jar or pot is a contained environment and does not process water the same as a garden. It is best to monitor the soil moisture as mentioned above.
Carrot seeds take 2 to 3 weeks to germinate, and it is important to maintain uniform moisture for that time. Carrot seeds germinate best between 7-30°C (45-85°F). They will germinate faster on the upper end of this scale, so it is beneficial to keep the jars in a warm spot. Carrots also grow best in full sun, so putting the jar on a window sill or sunny location will really help them grow and thrive.
Once you are sure that all the seeds have germinated, it is time to thin the seedlings. Choose which 2 or three seedlings you want to keep, and pull out the rest.
As your carrots grow, continue to provide adequate water so the roots will develop into a sweet, juicy snack.
Once your carrots reach the desired size, simply pull the carrots out of the jar and enjoy!
Growing carrots in a jar is an excellent project to do with children. It is easy to include them in all parts of the process. If you plant a seed right near the side of the jar, they can watch the carrot grow and develop.
One tip for making it easier for a child at planting time is to use pelleted seeds. These are seeds that have been coated in clay, making them bigger and easier to handle. But remember to teach that this is not what a carrot seed really looks like. It might be a good idea to break open one of the pellets to find the seed within.
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