Potatoes do best in cool weather so you want to plant them as early as possible to give them as much growing time as possible in temperatures between 50 and 80 degrees.
In northern areas gardeners aim to get seed potatoes in the ground in early spring and in southern areas with hot summers potato growers look to avoid the summer by planting in early fall or winter and harvesting before summer.
Regardless of where you live and what season you are planting in there are some common things that help when deciding when to plant potatoes.
Plant potatoes when soil temperatures average at least 45 degrees, with no hard frosts on the horizon, and no temperatures consistently over 85 degrees for the length of time it takes for the variety of potato you’re growing to reach maturity.
A good way to know the soil temperature has reached 45 degrees is to use a soil thermometer. This is an inexpensive garden tool that is basically a meat thermometer that reads down to lower temperatures.
To get an average soil temperature you want to measure at a time around 10 AM when the grounds not cold from the night and not inflated by the afternoon sun. Insert the thermometer all the way in the ground about 5 inches and let it stay there about five minutes. If it’s 45 degrees or more you’re good to plant potatoes.
Another marker of when to plant potatoes is about three weeks after the last frost. Consult a Farmer’s Almanac to find out the last frost date in your area. This number is based on the average last frost date of the past 100 years and is accurate 90% of the time. There is a section below on how to deal with frost.
If you are planting a late summer crop you want a variety that will be mature a week before the first fall frost. A hard freeze of 24 degrees or less ends the season definitively.
Cut potato plants down a week before a hard frost so your tubers can start to toughen up. Leave 2-3 inches above the soil to mark the location of the potatoes. If a hard frost does come get your potatoes out of the ground as soon as possible to avoid rot.
Can I Plant Potatoes In July?
You can plant potatoes in July but if you live in an area with hot summers where July and August average temperatures are above 80 degrees you could have limited success. There are varieties of heat resistant potatoes but there is no getting around the fact that potatoes are cool weather plants.
There are ways to keep the soil temperature down that are covered below.
A study done by the Agriculture and Agri-Food Canada’s (AAFC) Fredericton Research and Development Centre, found that out of 55 varieties the one that did the best still had a 73% weight yield reduction with high temperatures.
Here’s the full article where the lead scientist of the study says that there needs to be more work done to create a more heat resistant variety of potato.
If temperatures are regularly above 85 degrees you should try and shade the potato plants during the most intense sunlight of the day. Shade cloths are designed for this but you can use anything you can think of including bed sheets.
If you’re planting in containers just move them out of the sun during midday. You can also put pieces of cardboard with a slot for the plant stem and place the cardboard on top of the potted plants to keep the soil temperature down.
Make sure to water enough during hot spells.
Preparing Potatoes for Planting
The importance of pre-sprouting your potato seed should not be overlooked. This allows potato seed to hit the ground growing and utilize the early spring when the cool weather is just right for potatoes. It also prevents the rotting of potato seeds that are sitting inactive in the cold wet spring ground. Check this article out to see how to properly pre-sprout potato seed.
If you’re planting in a plot of land you should till the soil 12-18 inches down to break up any compacted soil and give the potato roots and tubers loose soil to grow into. This will also help dry and warm up the soil. Remember to rotate your potato crop to avoid disease in the soil and depletion of nutrients. Come up with a plan for fertilization.
You can do a soil test like farmers do to get an exact idea of soil nutrient levels and PH. You can choose to go with organic or standard fertilizers or a mixture of the two.
Organic Plant Magic is my favorite organic fertilizer. It has more micronutrients and strains of beneficial soil bacteria than other brands. Jack’s Classic is a good water soluble standard fertilizer with a N-P-K of 20-20-20. Check out this article for more information on soil for potatoes.
Can Potatoes Survive Frost?
Yes potato plants can survive light frosts of 28 degrees and above without damage to the plant. A moderate freeze of 24-28 degrees or a hard freeze of less than 24 degrees will likely damage or kill the green growth of the potato plant above the ground. If there is not an extended freeze and the weather warms back up the potato plant will likely survive and regrow.
Cover potatoes with tarps or plastic sheets or even bed sheets to keep the frost off of them. If the frost is going to be moderate to severe, less than 28 degrees, use several layers of covering. Use sticks or stakes to keep the covering from resting directly on the plants.
If potatoes do get frosted severely wait a day or two until you can tell for sure the green growth has died and then prune it back to an inch or so above the ground. Don’t sprinkle water on frosted plants as this heats the cells up too quickly and can cause more cell death.
Here is a fabric plant cover that protects from frost and allows sunlight in so it can stay in place during the early spring. It can provide peace of mind knowing the small plants are protected somewhat from the elements and can increase soil temperatures as well by keeping the warmth from the sunlight trapped in the cover.
Please comment below with your own thoughts on when to plant potatoes.