This year I’m doing a small test of whether chitting (sprouting) potatoes makes much difference. The raised garden bed above is planted with gold and red potatoes. Flags mark the rows where chitted potatoes were planted. Between the flags are rows of un-chitted potatoes. I’ll dig them up around mid-June and (maybe) see whether or how much chitting improved my yield.
I detest gardening by folklore.
And that’s why I plant my Irish potatoes on St. Patrick’s day. That sounds like folklore, but it’s not. In climate Zone 7, March 17 is just about four weeks before our expected last frost date. That’s commonly-recommended time to get potatoes, peas, and a few other cool-weather crops into the ground.
Instead, the folklore in this process is chitting, that is, sprouting the potatoes before planting them. Everybody tells you to chit your potatoes. But when you look carefully, nobody tests whether or not chitting makes much difference.
In theory, sprouting the potatoes before planting gives you a jump-start on the growing season. This matters — particularly in the South — as potatoes really do not like the heat. And it’s not just that the mid-summer heat kills them. It’s that once soil temperatures reach a certain level, they stop producing anything useful, and all you get is a few small, knobby potatoes.
In practice, chitting potatoes has all the earmarks of gardening folklore. It seems reasonable but a) commercial potato growers don’t chit, b) there’s little-to-no systematic evidence that chitting increases yields, and c) how-to-chit advice is all over the map — warm/cold, dark/light, short period/months — as if it didn’t really matter. That’s all laid out in Post G24-002.
One thing I’ve learned is that much frequently-repeated gardening advice is simply folklore. It’s something that made some sense to somebody somewhere, and then got mindlessly repeated without ever being tested. Some of it may be true. Most of it is not. For example, many commonly-cited methods for frost protection do nothing, including covering plants with plastic sheeting or thin floating row cover. But a mason jar provides excellent frost protection, Post G22-006.
This year I decided to do a little controlled trial of chitting. I bought two bags of organic potatoes at the grocery store, and randomized the potatoes into chit and no-chit groups. The no-chits went into the fridge for a month, the chits stayed out to sprout.
You don’t get a lot of “statistical power” out of the resulting 60-odd potato plants. But this little trial ought to be enough to tell me whether or not chitting has some profound impact on my potato yields (Post G24-002, Addendum).
I’ve now put those potatoes into the ground in as even a fashion as possible, to try to eliminate any difference between the chit and no-chit groups in terms of location, water, nutrients, and sunlight. To do that, I inter-planted the chit and no-chit potatoes, using surveyor’s flags to mark the rows with chitted potatoes. That’s as close as I can get to growing the two groups of potatoes under identical conditions.
If chitting matters greatly, it should show up as a “statistically significant” difference in yield, when I dig these up in June or so. In other words, a difference in yield so great that it is unlikely to have arisen merely by chance. But I’ve already done the math to show that any small difference between the chit and no-chit groups will be indistinguishable from random variation.
There’s only so much you can learn from a small bed of potatoes.
My advice for growing potatoes in Virginia: Heat is the enemy.
After four years of growing potatoes with varying rates of success, I think I finally understand what I should be doing, in Zone 7. So I thought I’d take a minute to lay out my rules for growing potatoes in a warm climate like that of Virginia.
To grow potatoes, in your back-yard garden, in Virginia:
- Buy organic potatoes at the grocery store.
- Buy gold potatoes, maybe red potatoes, but never russet potatoes.
- Chit them, maybe.
- Plant them as early as you reasonably can.
- After they sprout, add a light-colored mulch to keep the soil cool.
- Otherwise, follow standard potato-growing advice.
My advice for growing potatoes in Virginia mostly focuses on the main drawback of this climate, for potatoes: The heat. The list of top potato-growing states should give you a clue that the South is not a great place for growing potatoes.
Source: Potatopro.com
Here’s the reasoning behind my rules:
Rule 1 — buy organic potatoes at the grocery store — is based on the understanding that non-organic potatoes are typically sprayed with the potent herbicide chlorpropham (reference) to inhibit sprouting. That permanently damages the ability of the potato to grow. You can’t use that chemical on organic potatoes (see Post G22-004). Which is why, if you want to plant grocery-store potatoes, you should buy organic potatoes.
Rule 2 — buy gold potatoes. Potatoes come in short-season, medium-season and main-season (long-season) varieties. In Virginia, if you want your potatoes to finish before the heat of mid-summer, you want short-season potatoes. Based on my observation, the gold potatoes from the grocery store are short-season potatoes. They sprout sooner, come up quicker, and are ready sooner than the other commonly available varieties. (And, the Yukon Gold variety is, in fact, a short-season potato.) By the same reasoning, you should avoid russets (Post G23-035), as those are all main-season (long-season) potatoes that take about five months from planting to harvest. In Virginia, the heat will kill them before they are mature.
3: Chit? Well, that’s what I’m testing this year, but chitting is consistent with getting the biggest head-start on growing that you can.
4: Plant them early. Same logic. You want them to grow while its cool, and you want them to be as big as they are going to get before the heat of summer arrives. Sooner is preferred to later.
5: Light-colored mulch. The point of this is that, after the potatoes produce green above-ground sprouts, you want to keep the soil as cool as possible, for as long as possible. That’s because potatoes will not set new tubers once the soil is sufficiently warm, and they will produce few, small, knobby tubers if they are trying to set and grow tubers in very warm soil.
Rule 6: Everything else is standard. You can get the rest of the advice you need on potato-growing anywhere. Everything else is standard. Depending on your soil conditions, you’ll want to add fertilizer (particularly potassium). Weed and water. “Hill” them once the shoots are well up, to ensure that the base of the plant is covered with soil (or opaque mulch). Most people say you should nip off the flowers before they produce seeds (berries). Dig up potatoes at any time, but for maximum yield, let the foliage droop and die back before you harvest.
In any case, you can get the rest of the advice you need anywhere. It’s not as if I have any special insight into that. My only value added here is in (finally) figuring out that heat is the enemy of this crop, in Virginia, and for best results, you should plan every aspect of planting and harvest with that in mind.
