Several vegetables don't like compost or need far less than you'd expect. Root crops like carrots and parsnips top the list. Herbs like lavender and rosemary also do worse in rich soil. These plants grow better in lean, well-drained ground with little or no added compost.
I grew carrots in a bed loaded with fresh compost two seasons ago. Every single root came out forked and covered in tiny hair roots. They looked like little monsters. The next year I planted the same seed variety in a sandy bed with just a thin dusting of old compost. Those carrots grew long, straight, and smooth. The difference was night and day.
Too much nitrogen is the main problem. Rich compost floods the soil with nitrogen that pushes plants to grow big leafy tops. That sounds great until you realize the plant puts all its energy into leaves instead of roots or fruit. Tomatoes in a too much compost garden grow tall and bushy but set fewer fruits. Carrots fork because the rich soil gives the root no reason to dig deep for food.
Radishes run into a similar issue. They get woody and bitter in soil that's too rich. The plant rushes to produce leaves and flowers instead of building a nice fat root. Beans and peas are another surprise. They fix their own nitrogen from the air through bacteria on their roots. Adding compost gives them nitrogen they don't need. You end up with vines full of leaves and very few pods.
Plants that prefer lean soil share a few traits. They come from areas with sandy, rocky, or dry ground. Rosemary, thyme, and oregano produce their strongest oils when they struggle a bit in poor ground. Give them rich compost and they grow leggy with weak taste and soft stems. Native wildflowers and drought-hardy plants follow the same pattern.
You can spot the signs of a too much compost garden pretty fast. Look for dark green, floppy leaves that won't stand up on their own. Watch for lots of foliage but few flowers or fruits. Root crops that come out short and twisted are another clear signal. If you see any of these signs in your garden, cut back on compost for that bed next season and let the soil rest.
The fix is simple. Give your heavy feeders like squash, corn, and cucumbers a thick 2-inch (5-centimeter) layer of compost each spring. Use just a thin 0.5-inch (1.3-centimeter) layer for your root crops like carrots and beets. Skip compost for herbs that prefer dry, poor soil. This way every plant in your garden gets what it needs.
You can also test your soil before you add anything. A basic soil test from your county extension office costs about $15 to $25. It tells you your nitrogen, phosphorus, and potassium levels. If your beds already test high in nitrogen, you know to skip the compost on those plots. This takes the guesswork out of your garden planning.
Match your compost to the plants that want it most. Your squash, corn, and tomato beds will eat up every bit you give them. Your carrot rows and herb patches will thank you for holding back. Once you learn which crops want rich soil and which ones don't, your whole garden will produce better food with less waste. You'll save time and compost in the process too.
Read the full article: Compost Tumbler Guide for Beginners
