Ah yes, May 15. The unofficial gardening new year. Frost is (hopefully) gone, your plants are either in or about to be, and the sun has started cooking anything left in a black plastic pot.
But while this feels like the “go go go” moment of the season, it’s also when people start making classic mistakes—some minor, some unforgivable (looking at you, person who just pruned the lilacs).
This is your unofficial guide to what not to do in the garden after May 15. Whether you’re in USDA zones 4–8 or just pretending your backyard is a vineyard in Provence, you’ll want to read this before you go near your shears, hose, or seed packet.
Let’s get into it.
1. Don’t plant cool-season crops (unless you enjoy lettuce soup)
Spinach, lettuce, arugula, and peas had their chance. It was called March. By mid-May, planting them again is like sending a snowman into a sauna. They’ll bolt faster than a toddler with a juice box. If you missed the cool-weather window, chalk it up to experience—and plan for a fall crop instead.
2. Don’t prune your spring-flowering shrubs
Lilacs, forsythia, azaleas—if they’ve already bloomed, put the pruners down and back away slowly. These plants set buds for next year’s flowers almost immediately after blooming. Cut now, and you’re snipping off next year’s show. It’s like deleting your vacation photos before you take the trip.
3. Don’t forget the mulch… but don’t bury your plants either
This is your mulch deadline. Lay it down now, or you’ll be playing weed whack-a-mole in June. But don’t make mulch volcanoes around your plants. Smothering your perennials like overprotective parents won’t help anyone. Keep the mulch a few inches away from stems and trunks, or risk rot and bugs having a housewarming party.
4. Don’t transplant during high noon unless you’re into crispy seedlings
You know that moment in Westerns where the gunslinger squints into the sun at noon? That’s what your plants are doing too—only they don’t survive the duel. If you must transplant, do it in the late afternoon or early evening. Your baby tomatoes will thank you by not collapsing into a tragic heap.
5. Don’t keep ignoring weeds “just a bit longer”
After May 15, weeds go full Hulk mode. You leave them for a week and suddenly they’re taller than your toddler and angling for a spot on the HOA board. Get them out while the soil is still soft and the roots haven’t formed an underground union.
6. Don’t start fertilizing everything like you’re Oprah
“You get fertilizer! You get fertilizer! Everyone gets fertilizer!” Slow down. Some plants (especially natives and drought-tolerant varieties) don’t want or need the boost right now. And overdoing it can burn roots or send your plants into weird leafy overgrowth mode without flowers.
7. Don’t rely on your frost covers anymore
Unless you’re gardening in the Arctic Circle or a particularly temperamental mountain town, your row covers and frost blankets should be off by now. Leave them on and your plants may steam themselves into oblivion. Save those covers for late fall—when the frost fight begins again.
8. Don’t go overboard on watering
Yes, it’s warmer now. No, that doesn’t mean your plants need daily baths. Stick your finger in the soil. If it’s still damp a few inches down, skip the watering. Overwatering is sneaky—it invites fungus, root rot, and general plant depression. Trust your dirt.
9. Don’t delay pest patrol
Aphids. Cabbage worms. Powdery mildew. They don’t take long weekends. After mid-May, bugs and fungi shift into fifth gear. Check under leaves, look for nibble marks, and don’t wait until your kale looks like Swiss cheese. Early intervention = fewer tantrums later.
The Garden Has Entered Its Chaos Era
May 15 is when gardening goes from “cozy hobby” to “real-time strategy game.” Your plants are growing fast, the weather is getting pushy, and your decisions now can make or break your season.
So breathe deep. Drink water (yourself, not just the plants). And for the love of all that is green, don’t prune your lilacs.
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Daniel has been a plant enthusiast for over 20 years. He owns hundreds of houseplants and prepares for the chili growing seasons yearly with great anticipation. His favorite plants are plant species in the Araceae family, such as Monstera, Philodendron, and Anthurium. He also loves gardening and is growing hot peppers, tomatoes, and many more vegetables.