A lot of gardeners know how and when to plant potatoes, but come harvest time, the crops can leave a lot to be desired. Among the checklist of potato growing questions, the top one that needs answering is how deep to plant potatoes?
Getting the depth of planting wrong can be catastrophic leaving you with green potatoes that have a strong bitter taste due to toxic chemicals, mainly Solanine. The reason for this is sunlight.
Potatoes need heat to grow but they can never be exposed to direct sunlight. They do prefer full sun areas in your garden, but that’s only for the temperature. Not for the light.
To protect your potato crops from direct sunlight, it’s preferable to grow them in rows. Start with a long stretch of your garden that has a trench dug to a depth of 12” to 15”. What you’ll find though is by starting with just 4” to 6” of topsoil, you’ll be able to top the soil up as the plants begin to grow, which can be as fast as a few weeks.
By starting with a deeper trench, you’re able to then use what’s called hilling – a process of adding organic mulch on top of the compost to protect the potatoes from sunlight. Sphagnum peat moss, straw or other mulch such as organic wood bark and chips are common mulches for earthing potatoes.
The time to hill your potatoes is when the vines reach between 6” and 8”. By starting with a trench dug to up to 15” with between 4” and 6” of topsoil added over the seed potatoes, you’ll be able to hill your soil once or twice, giving them time to grow larger while protecting them from being exposed to direct sunlight.
Preparing Your Seed Potatoes for Planting
It’s beneficial to give your seed potatoes a head start by exposing them to light and room temperature before you plant them. Roughly two to three days is all that’s needed.
Using small seed potatoes that fit into an egg carton, but not touching, place them on a cool window sill to expose them to some light. Not direct, but partial sun.
When the seed potato is kept at temperatures of 50°F, it speeds up the chitting / sprouting process. That’s when the eyes/buds sprout from the seed potato. To make sure they do, when you’re putting the potato into the container, the side with the most eyes need to be facing upwards. That’s where the plant foliage is going to emerge.
The majority of seed potato varieties can sprout anywhere from three to a dozen sprouts. They’re best to have just three to four buds on them when planting, so if yours sprouts more, just apply pressure with your thumb to rub some of them off.
Too many buds can force the plant to divert energy into foliage growth instead of sprouting. You want as much of the energy being focused beneath the surface to encourage sprout growth instead of potato vines.
Another option for larger potatoes is to cut the potato into smaller 2” parts with each cut potato having at least two to three buds on them.
The seed potatoes will be ready to plant when the shoots grow to 1-inch.
Timing Your Planting for Maximum Yields
For the seed potato, it’s particularly important to use a mother tuber that’s certified. Not a random potato from the supermarket as those can pose a higher risk of disease.
Your local nursery is likely to have some available. Failing that, there’s a wide variety available online. Just make sure you’re buying organically harvested seed potatoes that’s certified as virus-free.
The ideal time for planting most seed potato varieties is between 2 and 4 weeks before the last frost date for your area. There’s a free lookup tool provided on DavesGarden.com that pulls data from the National Climatic Data Center showing the forecast for expected last frost dates by state across the US.
Use that data to schedule time for ground preparation so your garden is ready for sowing potatoes between 2 to 4 weeks of your last expected frost date.
Next is to make sure the soil is up to temperature before planting. Potatoes shouldn’t be planted in soil until it’s a stable 40°F / 4.4°C. A soil temperature probe comes in handy for this.
How Deep to Plant Potatoes in Grow Bags, Pots or Containers
If your garden soil isn’t sufficient for growing potatoes (4.8 to 5.5 pH) or if there’s loads of rocks and gravel in your soil that’s likely to hinder growth, you may need to use a potato grow bag instead. The same applies if you have a small garden, or no garden but a small balcony – grow bags can still produce decent potatoes in roughly the same time.
What you’ll need is a grow bag with sufficient capacity for the number of potatoes you intend to grow.
A good tip is that you can use a taller grow bag to tier your potatoes, rather than relying on only the bottom layer of your grow bag to sprout new potatoes.
In a grow bag, provided the growing conditions are kept right, it’s possible to plant potato tubers tiered. They do need sufficient grow space between them which is done by planting the tubers around 8” apart. As they only need 4” of multipurpose compost under them then another few inches of topsoil over them, it is possible to grow more using a taller container.
Depending on the size and height of your grow bag, you could plant four seed potatoes toward the bottom, cover it with a few inches of more compost, plant some more and repeat until you have multiple tubers planted.
If you’re planting potatoes in pots or a raised bed garden, tiering your potatoes over multiple layers is likely to be less effective due to the height restrictions but the same 4” to 6” of soil beneath and over your seed potatoes still apply. The more topsoil there is, the better your potatoes will be protected from sunlight.
If you have limited garden space and need alternatives that give you the depth you need for a good harvesting of potatoes, the video below gives you some frugal tips to grow more in less space: