After harvesting the last of my onions, I’m always excited to plan what comes next. There’s still plenty of potential for the garden to grow more food for fresh eating in the fall.

Rotating plant families is important for garden health. For an in-depth look at this topic and how it benefits your garden, check out my detailed guide on Understanding Crop Rotation. Now, let me share what I've learned from my own garden.

Suggested Crops for Post-Onion Planting by Zone and Type

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Nitrogen-Fixing Plants

• Peas
• Fava Beans

Since onions significantly deplete soil nitrogen, consider planting crops that restore this vital nutrient.

Right after harvesting onions, peas are my go-to choice. These nitrogen-fixing plants not only grow quickly but also replenish nitrogen levels in the soil. I have an article that details the process that beans and soil microbes use to create nitrogen nodules - it’s fascinating!

Fava beans are also great for mild winters and will overwinter in zones 7+ for a June harvest.

Leafy Greens

• Lettuce
• Bok Choy
• Spinach
• Kale
• Chard

Picture a mix of vibrant pink radicchio lettuce and the deep blues, greens, and purples of kale leaves, adding a splash of color to your garden and plate.

Lettuce, bok choy, and spinach are perfect plants to follow onions. If you had tried sowing salad greens earlier in the season only for them to bolt, now’s your opportunity for a second go at it.

Kale and chard are hardy choices that keep growing even with light frosts. Add a fabric row cover and get cut-and-come-again harvests of fresh greens throughout the winter! I am usually able to harvest from this pair until December or beyond!

They have different nutrient needs and don't deplete the soil as much, adding a fresh, vibrant touch to your garden and meals.

Root Crops with Different Nutrient Needs

• Carrots
• Beets

Carrots and beets do well in soil where onions were grown, benefiting from different nutrient requirements.

A bit of frost doesn't bother these veggies; in fact, it makes them taste sweeter. So, there's no rush to harvest them before the first frost.

Overwintering Brassicas

• Purple Sprouting Broccoli
• All-the-Year-Long Cauliflower

Although brassicas are heavy feeders, you can grow purple sprouting broccoli and all-the-year-long cauliflower to reap rewards in early spring.

Provide a bit of organic nitrogen-rich fertilizer or composted chicken manure to these crops to help boost their performance.

Cold Stratification Scatter Garden

If you’re within a week or two of your first frost before heading into a long winter, you can try a bit of chaos gardening with flowers that require a period of cold in order to germinate and thrive.

You’ll essentially be replicating nature - dropping the seeds now, letting winter do its thing, and then you’ll have a bed full of germinating beauties in the spring!

Note that biennials typically won’t bloom until year 2 growing in your garden, BUT plants established early like hollyhocks might give you a year 1 bloom. It’s worth an experiment!

Great options for a late-summer flower scatter garden:

• poppies (annual)
• echinacea (biennial)
• hollyhocks (biennial)
• milkweed
• penstemon
• nigella (annual)
• calendula (doesn’t need cold stratification but its seeds are hardy enough to over winter)
• borage (doesn’t need cold stratification but its seeds are hardy enough to over winter)

Some herbs that need cold stratification:

• anise hyssop
• rosemary
• wood betony
• lavender
• thyme

For more on cold stratification, I’ve got a full list of flowers, herbs, and veggies that need cold in order to germinate.

Cover Crops

• Hairy Vetch
• Winter Rye

Cover crops are key in regenerative gardening. Certain cover crops replenish nitrogen and overwinter, protecting soil from erosion after an onion harvest.

Hairy vetch is a favorite of mine because it combats soil diseases and pests while adding nitrogen. Its purple flowers also attract bees in spring.

If you’re a big fan of mulch (and who isn’t!?), you can grow your own by sowing a crop of winter rye right now.

What NOT to plant after onions

• Garlic: Although it’s convenient to sow fall-planted garlic after onions to let them overwinter, I wouldn’t recommend this UNLESS you had a crop of peas or another nitrogen-fixing plant in between. Garlic is a heavy nitrogen feeder like onions, and the soil might be too depleted or leave you needing to fertilize more than you would if you planted your garlic elsewhere. If that wasn’t enough, garlic and onions are in the same family and so it’s not a good crop rotation practice to plant them sequentially.
• Tomatoes: While you likely aren’t planting tomatoes right now unless you’re in zone 10 or above - just in case, you should know that a study from the Union Scientists of Bulgaria found that onions had an allelopathic effect on tomatoes, stunting their growth.

Personal Experiences and Tips

1. Timing: Plant beans right after harvesting onions for best results.
2. Water: Since you’ve likely not been watering your onions for the last few weeks for longer storage time, be sure to water your seeds in well. I like to saturate the soil both before and after sowing in this situation.
3. Soil Preparation: While onions are a root vegetable, they don’t really go that deep into the soil. Use a broadfork to prepare your garden bed, especially if planting carrots and beets in soil that is less than idea.
4. Observation: Keep an eye on plant health and pests.

Additional Tips Based on Growing Zone:

• For Zones 1-2, focus on early spring planting of frost-tolerant crops as soon as the soil can be worked.
• For Zones 3-4, after onions, utilize cold frames or row covers to extend growing seasons for leafy greens and root crops.
• For Zones 5-6, take advantage of the cooler fall temperatures to plant a second round of leafy greens and root crops after you harvest onions.
• For Zones 7-8, overwintering crops can be planted in fall for spring harvests. Brassicas are a great choice for this!
• For Zones 9-10 and 11-12, manage heat by providing shade and ample water for leafy greens planted post-onions.

Supporting Soil Health After Onions

Compost is my garden’s multivitamin. It enriches the soil, improves its structure, and promotes healthy plant growth. I make sure to add a generous amount before planting.

Once your plants have grown to around 3 inches, mulch around them with weed free grass clippings or organic straw to help keep moisture in during the heat of August and September. Heavier mulch applications in the autumn (perfect timing with fallen leaves!) will help your veggies to last longer beyond your frosts and even overwinter.

Yield Goals

When planning your post-onion planting, it’s important to consider your yield goals. To maximize yield, choose crops that thrive in the nutrient conditions left by onions and grow quickly for a bountiful harvest. Nitrogen-fixing crops like peas and fava beans are excellent for improving soil health and setting the stage for high-yield plants in the following season. Leafy greens such as lettuce, bok choy, and spinach can offer multiple harvests, especially if grown using cut-and-come-again methods. Additionally, overwintering crops like purple sprouting broccoli can provide valuable harvests during the early spring hunger gap, ensuring a continuous supply of fresh produce.

Gardening Styles

Different gardening styles can influence what you might choose to plant after onions.

For organic gardeners, legumes like peas and fava beans are excellent choices because they improve soil fertility naturally without synthetic fertilizers.

In permaculture gardens, incorporating a variety of crops to create a polyculture can enhance biodiversity and resilience. For example, interplanting leafy greens and root vegetables with nitrogen-fixers can create a balanced ecosystem that supports each plant’s growth and the overall health of the garden.

Traditional row gardening might focus more on sequential planting, ensuring that each crop benefits from the previous one’s soil improvements.

What are you planting after your onion harvest?

Gardening is a journey of learning and experimenting. By thoughtfully planning what to plant after onions, you’ll not only enjoy a longer period of garden-fresh food, but also contribute to a thriving garden ecosystem. Now go on and check that your onions are curing properly so you can mix those into meals with your fall harvests.

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