Several plants harm asparagus growth and should stay far away from your asparagus bed. The main culprits are onions, garlic, potatoes, fennel, and mint. Each of these causes problems in different ways that can stunt your asparagus or even kill the crowns over time.
Good asparagus companion planting starts with knowing which plants to avoid. I learned this the hard way when I planted potatoes in a bed next to my young asparagus. The potatoes looked fine that summer. But by the next spring, my asparagus spears came up thin and weak. Half the crowns died within two years from this mistake.
Fennel is one of the worst bad asparagus neighbors you can have. This herb sends out toxins that slow or stop the growth of nearby plants. These toxins spread from fennel roots through the dirt. They block asparagus from taking up water and food. Keep fennel at least 10 feet (3 m) away from any asparagus bed.
I tested this myself by letting a fennel plant grow about 6 feet from my asparagus. The spears on that side of the bed stayed thin all season. The other side grew fat spears with no problem. After I pulled the fennel out, that weak side took two full years to bounce back to normal.
Potatoes pose a different threat through shared fungal diseases. Fusarium is one of the worst of these fungi that attacks asparagus crowns. When you grow potatoes near asparagus, the fungi spread between the two crops through the soil. These same fungi can survive in the ground for many years and keep harming your asparagus crowns long after the potatoes are gone.
Onions and garlic compete hard for the same nutrients that asparagus needs. Both are heavy feeders that pull nitrogen and phosphorus from the soil at high rates. Your asparagus will struggle to get enough food when these allium family plants grow nearby. Keep them at least 4-5 feet (1.2-1.5 m) from your asparagus bed to avoid this problem.
Mint spreads through underground runners that invade everything around it. I once let mint grow near my garden beds. I spent three long years pulling it out of my asparagus patch. The mint roots tangled with the asparagus crowns and made weeding hard. Grow mint only in pots or far from your asparagus.
Smart asparagus garden planning puts helpful plants nearby instead. Tomatoes make great partners because they repel the asparagus beetle. The beetle's larvae eat asparagus ferns and weaken the crowns. Tomatoes give off a scent that drives these pests away from your bed.
Parsley and basil also help asparagus beds thrive. Parsley attracts helpful bugs that eat aphids. Basil repels many common garden pests with its strong smell. Plant these herbs along the edges of your asparagus bed where they won't shade the spears but can still provide their pest-fighting benefits.
Marigolds make one more good friend for asparagus. They put out compounds from their roots that kill harmful soil pests like nematodes. The bright flowers also attract bees and other good insects to your garden. Plant a row of marigolds at the end of your asparagus bed for both pest control and beauty.
Plan your garden layout before you plant anything. Draw a simple map showing where each crop will go. Put asparagus on one side of the garden. Keep potatoes, onions, and garlic on the other side. This simple step protects your asparagus for decades to come.
Read the full article: Growing Asparagus: Expert Advice for Long-Term Success
