If you’re a gardener, you’ve probably heard about the wonders of mushroom compost. But did you know some plants that dont like mushroom compost? This rich soil amendment isn’t a one-size-fits-all solution, and using it incorrectly can actually harm certain plants in your garden.
Mushroom compost is the spent growing medium from mushroom farms. It’s typically a blend of materials like straw, peat moss, and gypsum. After mushrooms are harvested, this leftover compost is pasteurized and sold. It’s prized for its ability to improve soil structure, retain moisture, and provide a slow-release of nutrients. However, its specific properties make it unsuitable for some plants. Knowing which ones can save you from stunted growth or even losing your favorite specimens.
Plants That Dont Like Mushroom Compost
This list covers common garden plants that often struggle in soil amended with mushroom compost. The primary reasons are usually related to high salt content, alkaline pH, or excessive nutrient levels.
Acid-Loving Plants (Ericaceous Plants)
Mushroom compost is often neutral to alkaline. This is a major problem for plants that require acidic soil to access nutrients properly.
- Rhododendrons & Azaleas: These shrubs will develop chlorosis (yellowing leaves with green veins) in alkaline soil, as they cannot uptake iron.
- Blueberries: They demand very acidic soil. Mushroom compost can raise the pH, leading to poor fruit set and yellow leaves.
- Camellias: Like rhododendrons, they thrive in acidity and will not perform well with mushroom compost.
- Heathers (Calluna & Erica): These groundcovers are adapted to low-pH soils and will struggle in alkalized conditions.
Plants Sensitive to High Soluble Salts
The composting process can leave behind soluble salts. Seedlings and salt-sensitive plants can suffer from “fertilizer burn,” where roots are damaged.
- Seedlings: Their tender roots are easily damaged by high salt concentrations. It’s best to use a finer, milder seed-starting mix.
- Ferns: Many native ferns are sensitive to salt and can develop brown, crispy fronds if the soil is too rich.
- Lupines: They prefer poorer, well-drained soil and can be susceptible to root burn from high salts.
- Potatoes: High salt levels can negatively effect tuber development and overall plant health.
Plants That Prefer Low-Nutrient or Specific Conditions
Some plants are adapted to thrive in nutrient-poor, sandy, or very sharp-draining soils. The richness of mushroom compost can cause lush, weak growth or root rot.
- Mediterranean Herbs: Lavender, rosemary, thyme, and sage need gritty, low-fertility soil. Mushroom compost retains too much moisture and nutrients, leading to root rot and woody, less fragrant growth.
- Succulents & Cacti: These plants require excellent drainage and low organic matter. Mushroom compost holds moisture, which will quickly cause their roots to rot.
- Native Wildflowers: Many are adapted to local, often lean, soil conditions. Introducing rich compost can allow more aggressive plants to outcompete them.
- Carrots and Parsnips: If the soil is too rich, these root crops may fork or develop excessive hairy roots instead of nice, straight taproots.
Specific Vegetable Garden Cautions
Even in the veggie patch, some plants need careful consideration. Tomatoes and peppers, for example, can sometimes handle well-aged mushroom compost, but fresh stuff may be too strong. It’s often better to use it in moderation for these. Beans and peas, which fix their own nitrogen, may produce more foliage and fewer pods if the soil is overly rich from mushroom compost.
What to Use Instead for These Plants
For acid-loving plants, use ericaceous compost or amend soil with peat moss (or sustainable alternatives like coconut coir) and sulfur. For herbs and succulents, create a mix with plenty of sharp sand, perlite, or grit. For seed starting, always use a dedicated, fine-textured seed compost. For native plants, try to mimic there natural soil as closely as possible, often using minimal amendments.
How to Safely Use Mushroom Compost in Your Garden
If you have mushroom compost and want to use it, follow these steps to avoid problems. A little care makes it a fantastic resource for the right plants.
1. Always Age or Leach It First
Fresh mushroom compost can be “hot” with salts. Let it cure in a pile exposed to rain for several months. Alternatively, you can leach it by thoroughly soaking it with water several times to wash excess salts away.
2. Test the pH
Get a simple soil pH test kit. If your compost tests alkaline (above 7.0), you know to avoid it for acid-loving plants. You can sometimes lower pH with sulfur, but it’s easier to just use it elsewhere.
3. Use It as a Soil Amendment, Not a Potting Mix
Blend it into your garden beds at a ratio no higher than 1 part compost to 2 parts native soil. It’s excellent for improving clay or sandy soils. Never use it as 100% of a planting medium.
4. Apply in Fall
Adding it to empty beds in the fall allows winter rains to leach salts and the compost to fully integrate with the soil before spring planting.
5. Great Plants for Mushroom Compost
Use it generously for lawns, most deciduous trees and shrubs, turf grass, and heavy feeders like squashes, cucumbers, and corn. Most ornamental flowers, such as daylilies and marigolds, also benefit from it.
Frequently Asked Questions (FAQ)
Why is mushroom compost bad for some plants?
Its high soluble salt content and alkaline pH are the main issues. Some plants are very sensitive to these conditions and will show signs of stress or nutrient deficiency.
Can I mix mushroom compost with other compost?
Yes, absolutely. Blending it with a more acidic compost (like leaf mold) or a lighter compost can balance its properties and make it suitable for a wider range of plants.
Is mushroom compost the same as mushroom soil?
Yes, these terms are generally used interchangably to describe the spent growing medium from mushroom production.
What plants benefit most from mushroom compost?
Lawns, most vegetable garden beds (except those for acid-lovers), many perennials, and trees or shrubs that tolerate a range of soil conditions love it. It’s fantastic for improving poor soil structure.
How can I tell if my plants are being harmed by it?
Look for leaf scorch (brown edges), yellowing leaves (especially on acid-loving plants), stunted growth, or wilting despite moist soil. These can be signs of salt burn or pH imbalance.
Understanding the needs of your plants is the key to sucessful gardening. While mushroom compost is a valuable tool, it’s not universal. By remembering which plants that dont like mushroom compost, you can allocate this resource to the plants that will truly thrive in it. Always observe your plants after amending soil and be prepared to adjust your practices. Your garden will thank you with healthier, more vigorous growth when each plant’s specific needs are met.