Idaho’s potato gardens are legendary for good reason – our growing techniques have been perfected through generations of trial and error. As summer winds down, what you do in these crucial weeks can make or break your potato harvest.
I’ve spent twenty years growing potatoes in Idaho’s variable climate, and I’ve learned that late-summer care is where the magic happens. The difference between an average crop and a spectacular one often comes down to these final weeks of attention.
These nine techniques represent the collective wisdom of Idaho’s most successful potato gardeners – myself included. I’ve seen firsthand how these small adjustments can double the size of tubers just when many gardeners mistakenly think their work is done.
1. Strategic Watering Adjustments
Many gardeners make the critical mistake of maintaining the same watering schedule all season long. During late summer, potato plants need a more calculated approach.
I reduce watering slightly about two weeks before harvest to toughen potato skins. This prevents the disappointing scenario of damaged tubers during digging. But don’t cut back too drastically – a gradual reduction works best in Idaho’s dry August heat.
2. Final Hilling Before Harvest
One final hilling session in late summer can dramatically increase your yield. This technique prevents those frustrating green potatoes that form when tubers get exposed to sunlight.
Using loose, well-draining soil, I carefully mound an additional 2-3 inches around each plant. The timing matters tremendously – I do this when plants are still green but have finished flowering. Many Idaho gardeners skip this final hill and miss out on protected, larger potatoes.
3. Mulch Management Magic
Late-summer soil temperature regulation is crucial for continued tuber development. Mulch acts as a natural insulator against Idaho’s temperature swings.
I apply a fresh 2-inch layer of straw mulch in August, keeping it away from direct contact with stems to prevent rot. This simple addition maintains consistent soil moisture and temperature. Without proper mulching, extreme temperature fluctuations can halt tuber growth prematurely.
4. Pest Vigilance Intensifies
Late summer brings unique pest challenges just when many gardeners let their guard down. Colorado potato beetles often launch their final offensive now, and aphids can suddenly multiply in August.
I inspect the undersides of leaves twice weekly, using a strong spray of water to dislodge aphids. For more serious infestations, insecticidal soap works wonders without harming beneficial insects. This vigilance in the final growing weeks preserves plant energy for tuber development rather than pest defense.
5. Balanced Late-Season Fertilizing
The fertilizer equation changes dramatically in late summer. Excess nitrogen now causes lush foliage at the expense of tuber development – a mistake I made for years.
I switch to a low-nitrogen, higher-phosphorus and potassium fertilizer about 60 days after planting. This encourages plants to focus energy on underground tuber growth rather than unnecessary foliage. A simple 5-10-10 fertilizer applied lightly works perfectly in Idaho’s mineral-rich soil.
6. Strategic Top Cutting
Cutting potato tops isn’t just folklore – it’s a strategic move that signals plants to finalize tuber development. I trim tops when most plants have yellowed and about two weeks before planned harvest.
Using clean shears, I cut stems about 2 inches above soil level, which helps toughen potato skins. This technique prevents the disappointment of immature skins that scrape off during harvest. The timing is crucial – too early and you’ll reduce yield, too late and you miss the benefit.
7. Harvest Timing Indicators
Reading your plants for perfect harvest timing is an art form most Idaho potato veterans have mastered. The classic sign – waiting until tops have been dead for 2-3 weeks – isn’t the whole story.
I dig a test potato when tops yellow significantly. The skin should resist scraping with my thumbnail. In Idaho’s climate, morning harvesting prevents tubers from heating up and deteriorating quickly. Many beginners harvest too early, missing out on that final size increase and proper skin setting.
8. Soil Temperature Monitoring
Few gardeners realize that soil temperature dramatically affects late-season tuber development. Potatoes essentially stop growing when soil temperatures rise above 80°F or drop below 50°F.
I use an inexpensive soil thermometer to track temperatures, adding extra mulch when needed to moderate heat. Idaho’s cool nights can help, but afternoon sun can still overheat soil. This simple monitoring prevents the disappointment of stunted growth during what should be the final bulking phase.
9. Curing Setup Preparation
Preparing your curing area before harvest ensures potatoes transition seamlessly from ground to storage. Many gardeners overlook this critical step and wonder why their potatoes don’t store well.
I set up a shaded, well-ventilated space with temperatures between 60-70°F and humidity around 90%. Simple supplies like clean cardboard and fans make all the difference. In Idaho’s dry climate, placing containers of water nearby helps maintain humidity during the crucial 10-14 day curing period.