Idaho isn’t called the Potato State for nothing – our local gardeners have mastered the art of growing perfect spuds through generations of trial and error. Late summer marks a critical period for potato plants when the right care makes all the difference between a mediocre crop and a bountiful harvest.
These time-tested secrets from Idaho’s most successful home gardeners can help anyone maximize their potato yield during those crucial August and September weeks.
1. Strategic Hilling Saves The Day
I’ve found that adding one final hill of soil around potato plants in late summer provides crucial protection. The extra soil layer shields developing tubers from sunlight that would turn them green and toxic.
Most folks stop hilling too early, but Idaho gardeners know better. We continue this practice through August, especially after heavy rains that might have washed away protective soil.
Use loose, well-draining soil for this final hill. Avoid compacting the mound, as potatoes need room to expand without resistance during these final growth weeks.
2. Morning Watering Schedule
Switching to morning-only watering helps Idaho potato plants thrive during late summer’s temperature swings. Early watering gives plants moisture before the day heats up while allowing foliage to dry completely before evening.
My neighbor lost half his crop to blight last year from evening watering. The moisture sitting overnight on leaves created perfect conditions for fungal diseases that spread rapidly through his garden.
Aim for consistent soil moisture – about an inch of water weekly. Irregular watering causes misshapen tubers and growth cracks, ruining otherwise perfect potatoes.
3. Mulch With Straw, Not Hay
Clean straw mulch works wonders for late-season potato beds here in Idaho. A 2-3 inch layer helps maintain soil temperature and moisture levels when August brings those scorching afternoons.
Last summer taught me a hard lesson when I used hay instead of straw. The hay contained weed seeds that competed with my potatoes, significantly reducing my yield.
Straw also creates a barrier against potato-loving insects that might otherwise make a home in your garden soil. Just keep it away from direct contact with stems to prevent rot.
4. Stop Fertilizing At The Right Time
Contrary to what you might think, Idaho potato experts actually stop fertilizing completely by mid-August. Continuing to add nitrogen encourages leafy growth when we want the plant’s energy focused underground on tuber development.
My grandfather always said, “Feed early, rest late” about his prize-winning potatoes. He’d apply a balanced fertilizer until flowers appeared, then let the plants redirect their energy to the tubers.
If your potato plants still look hungry in late summer, add only a small amount of phosphorus and potassium – never nitrogen – to support tuber growth without stimulating more leaves.
5. The Cut-Leaf Technique
Some Idaho gardeners swear by trimming about one-third of potato plant foliage in late August. This old-timer technique forces the plant to focus energy on tuber development rather than maintaining excessive leaves.
The first time I tried this, I was terrified I’d kill my plants! But cutting back some foliage actually resulted in larger potatoes that matured more quickly before our early frosts.
Use clean, sharp scissors and remove outer leaves first. Leave the central growth intact to continue photosynthesis while reducing the plant’s overall energy demands.
6. Companion Planting With Marigolds
Marigolds planted between potato rows create natural protection during late summer when pest pressure increases. Their strong scent confuses potato beetles and their root secretions deter harmful nematodes in the soil.
My potato patch suffered terrible beetle damage until an old Idaho farmer suggested this trick. Now I plant a row of marigolds for every two rows of potatoes, focusing on the French variety with its stronger pest-repellent properties.
For late summer protection, you can even transplant blooming marigolds from other garden areas to create a protective barrier around potatoes that are finishing their growth cycle.
7. Russet Variety Rotation
Smart Idaho gardeners don’t plant the same potato variety in the same spot year after year. We’ve learned that rotating between different russet varieties improves both soil health and yields.
My family alternates between Russet Burbank and Russet Norkotah, which have different disease resistances and soil preferences. This simple rotation has virtually eliminated the scab problems that once plagued our garden.
Even within the russet family, different varieties take different nutrients from the soil, so rotation prevents depletion while naturally interrupting pest and disease cycles that would otherwise build up.
8. Harvest Timing By Leaf Color
Idaho’s best potato gardeners ignore the calendar and watch for visual cues instead. When about 75% of the foliage turns yellow, it’s time to stop watering completely to begin hardening the skins.
I learned this from my neighbor who’s been growing potatoes for 50 years. He taught me that harvesting too early results in thin-skinned potatoes that don’t store well, while waiting too long risks frost damage.
Wait 2-3 weeks after the yellowing and water stoppage before harvesting. This timing allows skins to toughen properly, which dramatically improves storage life through our long Idaho winters.