I like growing potatoes and recommend them as a food crop, but you have to grow them right.
Potato plants will not grow potatoes if the plants have too little water, fertilizer, sun, or room to spread their roots. Potato tuber formation and growth are regulated by plant growth hormones which are affected by plant stress, temperature, and day length. Potatoes may not form in hot or dry weather.
It’s an annoying and serious problem, and hopefully, you don’t have to experience it twice. There’s a lot to this article, but it’s worth the read.
5 Things That Stunt Potato Tuber Growth
The most common reason why potatoes didn’t grow well is probably lack of water. Without a good supply of water, potatoes will not have the ability to take up adequate nutrients from the soil, and they will not be able to pump the tubers full of starch.
Water is the delivery service for plants. It transports and delivers all the nutrients that a plant needs both to the plant and throughout the plant. Without enough water, the plant will be stunted because it is not able to take up the nutrients required to produce more building blocks for plant growth.
Healthy potato plants are over 80 percent water and are constantly cycling water in and out of the plant. If just once, the plants get to the point where the plant gets wilty, the roots will be stunted, and the plant will not take up nutrients well after that.
Generally, we say that potatoes need a minimum 1-inch of irrigation a week to stay happy. If you dig 6-inches deep into your soil and don’t see a moist zone, your soil is out of water. If you notice the soil getting quite dusty while you are working in it, it’s probably out of water.
If you can at all help it, don’t let potato soil dry out until the plants begin to brown and die back at the end of the season.
Too little fertility is the second reason why potatoes may have poor yields.
Potatoes are heavy-feeding plants, like all high-yielding crops. Potatoes take about 200 pounds of nitrogen per acre, which is about 1/2 pound per 100 plants. They often need about the same amount of nitrogen as corn.
Main nutrients for potatoes, in order from greatest to least:
- Nitrogen 200 lbs./acre
- Potassium 200 lbs./acre
- Calcium 50 lbs./acre
- Magnesium 35lbs./ acre
- Phosphorus 30lbs./acre
- Sulfur 13lbs./acre
I wrote an article on growing big potatoes that talks more about fertilizing. Here’s a link to it.
That’s an approximate nutrient need, but the ratio is what’s more important here. Nitrogen and Potassium are needed in about equal amounts. But, extra nitrogen is often needed because nitrogen is more volatile and easily lost from the soil. We’re lucky here to have a lot of calcium in the well water, so that’s covered.
Water carries nitrogen away through the soil, rain can wash it away, and some is lost from outgassing to the air. Often, an extra 15-25 percent is used. Also note that potatoes use a lot of calcium and magnesium, but need very little phosphorus, as with most plants. People don’t always realize that.
But, nitrogen is usually the one to be moist deficient and is generally the biggest factor in getting a good crop. It’s considered the most limiting nutrient.
Too much nitrogen will stunt tuber growth. Since we’re talking about nitrogen, I need to mention over-nitrogenating the soil. That’s bad. Potatoes need a lot of nitrogen, but too much nitrogen without the other nutrients will stunt the plant’s tuber growth.
Excess nitrogen can keep the plant in the early growth stage and delay the tuber bulking stage. The plant’s life cycle is mainly regulated by the seasons. Too much nitrogen, delaying tuber growth, often means the plant will die off before the tubers are full-grown.
I did that this year. My records got messed up and I overfertilized a bed of potatoes. It yielded half what I expected, and the potatoes were mostly quite small. I’ll remember that next year. There’s no shame in making a mistake, only in not learning from it.
Heat inhibits plant hormones responsible for growing tubers. Potatoes tubers grow best in 65-75 degree weather. That’s when the series of hormones that cause tuber growth and bulking are produced the most. Above 75 degrees, those hormones lessen. Above 85 degrees, it’s quite significant.
Potatoes produce virtually no tubers with a daytime temperature above 94 degrees. That completely shuts down the tuber growth hormones. It takes extra work to get a decent potato harvest in a warmer climate, such as growing under a shade cloth.
Spacing plants too closely will greatly stunt tuber size and development. Potatoes are a big game of plant spacing. You want them as close as you can so the soil beneath is shaded, keeping the roots as cool as possible. But, too close of spacing creates too much competition for nutrients.
For a better per-plant yield, plant potatoes a foot apart down a row and have two-three feet between rows. My Agricultural Extension recommends 2 feet between rows to keep things shaded. Even if you put enough fertilizer down, plants’ roots will not get what they need with too close of spacing.
Troubleshooting Small or No Potatoes
To troubleshoot a low potato yield, let’s consider all the factors.
- loose soil that rain and roots can penetrate
- Water in abundance, the soil never drying deeply
- Fertilizer in adequate amounts
- Good soil organic content to hold moisture and fertility, and to feed soil biology
- Cool weather. 40-50 degree soil at planting, temperatures below 90 degrees, and cooler nights
- Stress-free from diseases or pests
- Little to no soil compaction from walking or driving between rows.
The first year I grew potatoes, I harvested an embarrassing two little tubers per plant. It was pathetic. Looking at the loss above, the two biggest mistakes were obvious. First, I planted late. Planting in soil above 50 degrees can cause less root growth. Potatoes like 40-45 degree soil to start.
Secondly, I didn’t water much. Not near enough for a soil bare of organic matter. The dirt was a sandy, pale, orange color, dry, and hard as a rock from natural cementation. I did fertilize but was careful not to overdo it. So, the problems were not enough water, poor soil, and planting late in the season.
In my climate planting late isn’t so bad on its own, but combined with other problems, it was a game-losing situation. The following year, I loosed the soil more, planted a month earlier, and watched once a week. I harvested twice as much.
I have an article on watering potatoes with a bit more information. Here’s a link to it.
This year, I had 2 beds that grew a lot of small potatoes, some plants not having any to find. I definitely needed to learn from this. I planted three rows in a 3-foot wide bed. The spacing is too close for nice big potatoes. I also noticed the soil was very compacted in the two outside rows. Apparently, I wasn’t stepping as carefully on the pathway as I thought. It was compacted and hard from walking too close to the plants. Lesson learned.
The second area really left me disappointed. no one walked there, it was watched regularly and fertilized exactly like the 6 other rows in the same plot. Yet, the soil was super dry and pretty hard.
The difference was, they were crowded by another crop. I planted a row of Jerusalem artichoke to keep erosion down on the hill’s edge.
The Jerusalem artichoke roots had spread to the potatoes and used up all the available water in their 8-10 foot tall stems. A soil test showed that the fertility was lower there too. I also noticed that, although I thought I planned for it, the potatoes were just too shaded from the taller crop.
So, yeah, don’t do that. Well, I hope you learned something from this article. Leave a comment if you have one, it’s always good to share information and I’m willing to try and answer any questions you have.