How to Prevent and Manage White Rot on Onions and Garlic

There’s nothing more gutting than gently pulling up what you thought was a perfect garlic bulb, only to find it mushy, mouldy, and riddled with fluffy white fungus. White rot is a soil-borne fungal disease that targets alliums, especially onions and garlic and once it sets in, it can linger in the soil for years.But don’t panic! With a few proactive steps, you can prevent and manage white rot on onions and garlic to safeguard our future harvests.

What Is White Rot?

White rot is a fungal disease that specifically attacks the roots and bulbs of allium crops. It’s one of the most serious diseases for onion and garlic growers because:

• It lives in the soil and can survive for up to 15-20 years
  
• It spreads easily through infected sets, soil, compost, and tools
  
• Once present, there’s no chemical cure, only prevention and good garden hygiene

Symptoms include:

• Yellowing, wilting, or stunted growth
  
• White, fluffy fungal growth around the bulb
  
• Small black dots (sclerotia) in the soil or on roots
  
• Rotting of the bulb, often before it fully matures

Start with Clean Sets and Seed

We always start with certified disease-free onion sets and garlic cloves from a trusted supplier. Avoid:

• Swapping sets with other gardeners unless you’re sure they’re clean
  
• Replanting cloves from a previous year’s crop if white rot was suspected

One bad bulb can introduce thousands of spores into otherwise clean soil.

Rotate Crops (Religiously!)

White rot spores are highly persistent. That’s why crop rotation is absolutely essential:

• Try not to plant onions, garlic, leeks, or shallots in the same bed for at least 4-6 years
  
• Use a rotation plan that separates alliums from other crops like brassicas, roots, and legumes

Also avoid planting alliums where ornamental alliums (like chives) have been grown.

Maintain Impeccable Soil Hygiene

If there’s one place to be a garden neat freak, it’s your allium bed. You can:

• Clean tools and gloves thoroughly between uses
  
• Avoid walking on or moving soil from infected areas to clean beds
  
• Never compost infected material, burn or dispose of it off-site

Keeping soil clean prevents unintentional spread of spores from one bed to another.

Use Natural Deterrents

Although there’s no cure once white rot is in the soil, you can make life harder for it:

• Apply sulphate of potash in the autumn before planting, it strengthens cell walls and can reduce susceptibility
  
• Mix garlic powder into the soil in late summer to trick dormant spores into germinating before planting season, when no host is present (known as “suicide germination”)
  
• Maintain well-drained soil, white rot thrives in wet, heavy conditions

Raise Your Beds and Improve Drainage

White rot is more aggressive in wet conditions. To keep things dry underfoot, you can try:

• Grow onions and garlic in raised beds or well-drained rows
  
• Mix grit or sharp sand into clay soils
  
• Avoid watering too frequently once bulbs begin to swell

A drier soil environment makes it harder for the fungus to thrive.

Remove Affected Plants Immediately

If you see signs of white rot mid-season:

• Pull up infected plants right away, don’t leave them to rot in place
  
• Remove a generous scoop of surrounding soil
  
• Clean tools immediately
  
• Consider quarantining that bed from alliums for future seasons

Early action can help limit the spread within a single growing season.

Grow in Containers or Clean New Beds

If your soil is infected, all’s not lost! You can still grow alliums by:

• Using large containers or grow bags filled with fresh, sterile compost
  
• Building new raised beds with imported topsoil and compost
  
• Trying ornamental alliums in infected soil, just don’t eat them!

These methods let you enjoy growing garlic and onions without risking reinfection.

White rot is one of the more frustrating garden challenges, but it’s not unbeatable. With careful planning, clean planting, and a solid rotation system, you can prevent and manage white rot on onions and garlic and still enjoy plump bulbs and fragrant harvests for years to come.