05/25/2026
Some garden advice gets repeated so often it stops being questioned. These five sound right — and aren't. 🌿
MYTH 1 — GRAVEL IN THE BOTTOM OF POTS IMPROVES DRAINAGE:
What actually happens: adding a gravel layer creates a perched water table. Water doesn't move from a finer medium (potting mix) into a coarser one (gravel) until the finer zone is fully saturated — so the gravel layer raises the wet zone directly into the root area, not below it. A continuous mix of potting soil with perlite mixed throughout drains better than any layered pot. The fix is simple: drill more holes in the bottom and use perlite throughout the mix, not gravel underneath.
MYTH 2 — WATERING IN MIDDAY SUN BURNS LEAVES:
Water droplets on smooth leaves don't focus enough light to scorch plant tissue — this has been tested in controlled conditions and the burn simply doesn't happen at realistic droplet sizes on most plant surfaces. There are good reasons to water in the morning: less water is lost to evaporation, and foliage dries before evening when fungal infection risk is highest. Water early for those reasons — not because of a sunburn effect that doesn't actually occur. Exception: some waxy or hairy-surfaced leaves in certain succulents and ferns may respond differently.
MYTH 3 — EGGSHELLS ADD CALCIUM QUICKLY:
Eggshells are among the slowest-decomposing materials in garden soil. Coarse pieces tossed into beds sit there largely unchanged for two to five or more years before releasing anything plants can use. If you want eggshells to contribute calcium in one season, grind them to a fine powder. If you need rapid calcium availability — for blossom end rot or other acute deficiencies — gypsum or lime with a soil test is far faster. The main functional value of eggshells is as a physical slug barrier at the soil surface, not as a nutrient source.
MYTH 4 — USED COFFEE GROUNDS ACIDIFY SOIL:
Brewing extracts most of the acid from the grounds. Used grounds test close to neutral pH. They won't lower soil pH for blueberries, azaleas, or rhododendrons the way most gardeners assume. They are useful as a nitrogen source in compost. Don't spread them thick on the soil surface — they form a dense hydrophobic crust that repels water. Mix them into compost or work them into the soil instead of using them as mulch.
MYTH 5 — MARIGOLDS REPEL MOST GARDEN PESTS:
French marigold (Tagetes patula) roots release alpha-terthienyl, a compound that suppresses specific plant-parasitic nematodes in the soil. That is real and documented — but it's underground, it's nematode-specific, and the effect requires growing marigolds as a cover crop and tilling them into the soil at the end of the season for maximum impact. Marigolds don't repel aphids, beetles, caterpillars, or the vast majority of above-ground pests. The visual presence of marigolds among tomatoes is not a pest deterrent for anything except those specific soil nematodes. French and Mexican marigolds (T. patula and T. minuta) have the nematode-suppressing effect; African marigold (T. erecta) is much less effective 🌱
Five corrections. Same garden. Better decisions.
