Which Plants Don't Like Compost? UK Gardening Guide

If you’ve ever dumped a wheelbarrow of rich, dark compost into your flower bed and watched your plants wilt instead of thrive, you’re not alone. Compost is often called black gold-but it’s not magic for every plant. In the UK’s damp, cool climate, some plants simply can’t handle the extra nutrients, moisture, or altered pH that compost brings. Knowing which plants don’t like compost can save you time, money, and a whole season of failed growth.

Why Some Plants Hate Compost

Compost is packed with nutrients, holds water like a sponge, and slightly lowers soil pH over time. That’s great for tomatoes, cabbages, and most perennials. But plants evolved in poor, rocky, or sandy soils don’t need-or want-this kind of attention. They’re adapted to low-nutrient environments. When you feed them compost, it’s like giving a fasting person a five-course meal. Their roots get overwhelmed, leaves turn yellow, and growth stalls.

In the UK, where rainfall is high and drainage can be poor, compost can make things worse. It retains moisture, which leads to root rot in plants that prefer dry feet. It also boosts nitrogen levels, which can cause leggy, weak growth in species that bloom best under stress.

Plants That Don’t Like Compost

• Heathers (Calluna vulgaris) - These classic UK garden staples thrive in acidic, sandy, low-nutrient soil. Compost, especially if it’s made from food waste, often contains too much nitrogen and can raise pH slightly. That’s enough to kill them. Plant heathers in pure ericaceous compost or sharp sand mixed with peat-free loam.
• Lavender - Lavender needs sharp drainage and low fertility. Too much compost leads to spongy soil, root rot, and leggy stems that flop over. In Brighton’s coastal gardens, where rain is frequent, compost-heavy soil is a death sentence for lavender. Stick to gritty, chalky, or stony soil. A handful of horticultural grit at planting is better than a bucket of compost.
• Succulents and Sedums - Even hardy varieties like Sedum spectabile or Sempervivum tectorum hate rich soil. They store water in their leaves and evolved in rocky crevices. Compost holds too much moisture. If you’ve seen your sedum turn mushy in spring, compost is likely the culprit. Use a mix of 70% loam and 30% sharp sand or perlite.
• Rock Roses (Cistus) - These sun-loving shrubs are native to the Mediterranean. They need alkaline, free-draining soil. Compost, especially leaf mould or manure-based, increases acidity and water retention. In wet UK winters, this combination kills them. Plant rock roses on a slope or raised mound with crushed limestone added to the hole.
• Wildflowers - Many native UK wildflowers like Orchis mascula (early purple orchid), Campanula rotundifolia (harebell), and Lotus corniculatus (bird’s-foot trefoil) grow naturally in nutrient-poor grasslands. Adding compost encourages aggressive grasses and nettles to take over, crowding out delicate wildflowers. For a wildflower meadow, start with bare, low-fertility soil. Don’t fertilise. Don’t compost. Let nature do the work.
• Alpines - Plants like Draba, Phlox subulata, and Thymus serpyllum are adapted to thin soils on mountain slopes. Compost turns their perfect drainage into a swamp. Use a mix of equal parts loam, grit, and perlite. Avoid any compost unless it’s specifically labeled as ‘alpine mix’.

What About Roses? Do They Like Compost?

Roses are often confused here. They do benefit from compost-but only if it’s used right. A thin layer (1-2cm) of well-rotted compost around the base in early spring helps retain moisture and feeds slowly. But digging compost into the planting hole? Bad idea. It encourages roots to stay in the hole instead of spreading into the native soil. That makes them vulnerable in drought. Instead, dig a deep hole, backfill with native soil, then top-dress with compost. This mimics how they grow in the wild-roots deep, surface mulched.

Soil Testing: The Simple Way to Know

Not sure if your soil is too rich? A simple test takes five minutes. Dig a small hole about 30cm deep. Take a handful of soil and squeeze it. If it forms a tight ball that doesn’t crumble, it’s heavy and likely rich in organic matter. That’s a red flag for compost-sensitive plants. If it crumbles easily, you’re probably safe.

For a more accurate check, use a home soil test kit (available at garden centres). Look for nitrogen levels above 20 ppm and organic matter above 5%. If both are high, hold off on compost for plants that prefer lean soil.

What to Use Instead of Compost

You don’t need to leave these plants hungry. Here’s what works better:

• Grit or sand - For lavender, rock roses, and alpines, add 30-50% horticultural grit to the planting mix. It improves drainage and mimics natural rocky soils.
• Leaf mould - If you must add organic matter, use leaf mould (decomposed leaves, not kitchen scraps). It’s lower in nutrients and better for acid-loving plants like heathers. But even then, use sparingly.
• Straw or wood chip mulch - These break down slowly and don’t boost nitrogen. Great for suppressing weeds without feeding the soil too much.
• Coarse bark - Useful for acid-loving plants. Avoid fine bark dust-it compacts and holds water.

Common Mistakes UK Gardeners Make

Here’s what goes wrong in real gardens:

• Adding compost to a wildflower meadow because ‘it’s good for the soil’-ends up with nettles and docks instead of orchids.
• Planting lavender in a border full of mushroom compost-plants die within a year.
• Using bagged ‘all-purpose compost’ for succulents bought from a supermarket-root rot by July.
• Assuming ‘organic’ means ‘good for everything’-compost isn’t a universal cure. It’s a tool. Use it wisely.

The biggest mistake? Treating compost like fertilizer. It’s not. It’s a soil conditioner. Some plants need conditioning. Others need starvation.

When in Doubt, Go Lean

It’s easier to add nutrients later than to remove them. If you’re unsure whether a plant likes compost, plant it in poor soil first. If it struggles, then add a tiny bit of compost the next year. Most compost-hating plants will reward you with stronger stems, better blooms, and longer life if you give them less, not more.

In the UK, where rain and cool summers make soil naturally fertile, it’s easy to overdo it. The secret isn’t adding more compost-it’s knowing when to leave it alone.