The herbs unsuitable for indoor growing are horseradish, fennel, lovage, and dill. These plants grow massive roots that pots cannot hold. Your windowsill garden will never give them the space they need.
I learned this the hard way when I bought a fennel seedling at the farmers market. The plant looked healthy for about three weeks. Then it turned yellow and stopped growing. When I pulled it out, the taproot had hit the pot bottom and started circling back on itself.
My neighbor made the same mistake with dill the following spring. Her plants shot up fast, then bolted to seed before making any usable leaves. She called them the worst herbs for indoors she had ever tried to grow. We both learned that some plants just need outdoor space.
Herbs that don't grow indoors share one thing in common. They need 12 or more inches (30+ cm) of soil depth to make healthy roots. Standard pots rarely offer this much space. Even your largest decorative containers fall short of what these plants need.
Penn State Extension lists large-rooted herbs as the main group to avoid indoors. Horseradish grows roots that reach two feet deep in outdoor beds. Fennel sends down a thick taproot that needs room to spread. Lovage becomes a massive plant that can hit six feet tall outside.
Dill has problems beyond just root depth. This herb bolts fast in warm indoor air and hates being moved. The shock of going from pot to pot often kills it outright. You will have better luck with dill seeds planted straight into outdoor soil.
You can find good swaps when you want similar flavors. Chives offer a mild onion taste that works in recipes calling for fennel. Tarragon gives you that anise-like flavor in a plant that grows well in pots. These herbs to avoid indoors have better options you can try instead.
Stick with compact herbs bred for container life if you want success. Basil, parsley, mint, oregano, and thyme all produce well in standard pots. You can grow them in six-inch containers and harvest fresh leaves all year long.
Save the large-rooted herbs for outdoor beds where they can spread out. Your indoor garden will thrive when you pick plants that fit the space you have. Focus on what works and you will enjoy fresh herbs from your kitchen windowsill every day.
Read the full article: Growing Herbs Indoors: Complete Guide for Beginners
