BLog

Summer in Minnesota is a rollercoaster. One day it’s 75 degrees and breezy. The next, it’s humid, muggy, and 90 degrees. The exhaustion we feel from that sudden heat? Our plants feel it too.

Heat waves stress plants in the same way they stress us — dehydration, energy depletion, vulnerability to illness. But unlike us, plants can’t grab a cold drink or retreat inside. They depend entirely on you to give them what they need to survive.

Here’s everything you need to know about caring for your garden during a heat wave — and the common mistakes that make things worse.

1. Planting When It’s Over 90°F

New plants are already vulnerable — they’re establishing roots, adjusting to a new home, and using all their energy just to survive. Add extreme heat to that, and they wilt, struggle, or die entirely. Seeds won’t sprout when temperatures are too hot either. The soil is too hot, the moisture evaporates too fast, and the seed can’t germinate.

Planting for success:

• Don’t plant or transplant anything when temps exceed 90°F: Wait until cooler days return. Early morning or late afternoon planting (when temps are cooler) are better in high temps.
• Perennials can be safely moved and divided once the heat subsides or in fall. If something didn’t work this year, mark it and move it when temperatures cool.

2. Fertilizing During High Heat

When plants experience extreme heat, they’re in survival mode. They’re focused entirely on conserving water, not pushing out new growth. Fertilizer — especially chemical fertilizers — can actually burn delicate root systems and stems when plants are heat-stressed. It’s like asking someone to run a marathon when they’re already dehydrated.

What to do instead:

• Skip fertilizing when temperatures are 85°F or higher: Wait for cooler days to resume feeding annuals, perennials, and anything else. You’re not wasting the fertilizer by waiting — you’re preventing plant damage.

3. Pruning During Peak Heat

Heavy pruning removes foliage (which the plant needs to photosynthesize and produce energy), reduces the plant’s ability to cool itself, and makes it more vulnerable to drying out.

When to properly prune:

• Don’t prune for aesthetics during a heat wave: Follow our pruning schedule when temps are below 90ºF.
• Exceptions: Remove branches that are diseased, dead, or damaged immediately. This is actually important during heat waves because Minnesota’s humidity (which often accompanies heat) creates perfect conditions for fungal disease. Getting diseased material off your property quickly prevents spread.

4. Watering Incorrectly (Too Much or Too Little)

Heat waves create a “Goldilocks” watering situation — too much is as dangerous as too little. Overwatering leads to soggy roots and root rot, making it even harder for plants to recover from heat stress. Under-watering leaves them with no resources to survive peak afternoon sun.

How to correctly water:

• Water deeply at the base of the plant, before 10 AM: Morning watering gives plants the hydration they need to survive peak afternoon heat.
• Check soil moisture before watering: Dig 1–2 inches into the soil. Does it feel moist? Wait. Is it dry? Water deeply.

Container plants may need watering 1–2 times daily depending on size, plant type, and heat intensity. Check daily.

Newly planted perennials, shrubs, and trees need water when the top 1–2 inches of soil feel dry. They’re still establishing roots and depend on consistent moisture.

Native plants (once established) need minimal supplemental water even during heat waves. Their deep roots find moisture deep in the soil. But new native plantings should be watered the same as other new plants — when top 1–2 inches are dry.

5. Watering in the Evening

Evening watering seems logical — less evaporation, more time for roots to absorb water. But it’s actually the worst time to water. Plants need water in the morning so they have hydration to survive peak afternoon sun. They can’t use water that arrives at 6 PM when the hottest part of the day has already passed.

Plus, wet foliage overnight increases disease risk. Leaves need time to dry during the day to prevent fungal issues.

What to do instead:

• Always water before 10 AM: This gives plants the hydration they need when they need it most.

6. Skipping Mulch

Mulch is one of the most powerful heat-wave tools you have. It retains soil moisture (preventing evaporation), keeps soil cooler, and suppresses weeds — all of which matter desperately during heat waves.

If you still need to mulch:

• Apply 2–3 inches of mulch around garden beds, perennials, shrubs, and trees: Leave space around the base/trunk of plants so mulch doesn’t trap moisture against the plant (which causes rot).
• In a pinch, any amount of mulch helps: It’s not too late to mulch in mid-heat wave. Every inch reduces evaporation and keeps soil cooler.
• Bonus: Fresh mulch also improves the appearance of your landscape.

7. Not Harvesting Ripe Fruit and Vegetables

Bearing fruit takes enormous energy and resources. Plants already stressed by heat can’t afford that extra demand. Leaving ripe fruit on the plant also attracts pests — and pests are more active during peak summer heat.

What to do instead:

• Harvest ripe tomatoes, peppers, squash, beans, and other produce regularly: This signals to the plant that it’s doing its job, encourages more production, and — importantly — conserves plant energy during heat stress.
• Ripe berries, stone fruits, and other produce should also be harvested promptly. This reduces pest pressure and keeps the plant focused on survival, not seed production.

8. Forgetting to Take Care of Yourself

You’re working as hard as your plants to keep them alive during a heat wave. Don’t neglect your own needs! Gardening in a heat wave is physically demanding work. You’re standing in the sun, carrying water, kneeling in hot soil, checking plants constantly. Heat exhaustion is real.

What to do instead:

• Drink plenty of water: More water than you think you need!
• Wear protective clothing or sunscreen: UV exposure adds stress on top of heat.
• Take breaks: Sit in the shade, cool down, rest. You can’t help your plants if you’re exhausted.
• Water in the early morning or evening when it’s cooler, not in peak afternoon heat.

Your plants need you healthy and present. Take care of yourself first.

The Heat Wave Mindset

Heat waves are temporary. They feel eternal when you’re in the middle of one, but they pass. Your job is to keep plants alive and relatively comfortable until cooler days return.

It’s not the time to try to improve or change your landscape during a heat wave. Just maintain. Water deeply. Mulch. Avoid stress. Remove disease. And wait for days below 90ºF.