Growing big potatoes has become much harder in recent years as erratic shorter growing seasons caused by climate change has massively impacted their growing windows, but freak events like the recent giant potato news in New Zealand have given gardeners reason to be hopeful.
If you’re wondering why your homegrown potatoes are smaller than you expected, you’re in the right place. Potatoes are reasonably simple crops to grow (other than the constant risk of blight caused by humidity, tight spacing and infected soil) but nevertheless, there is some skill involved in rectifying a small potato crop and renovating your ground for the following season.
What to do to avoid growing small potatoes
Ensure that they have great soil conditions
Potatoes need loose, rich soil to grow big. Like any root vegetable they need space to breathe, and soil that’s loose enough for them to grow into.
Potatoes grow on the roots sent out from seed potatoes (last year’s crop), so the easier it is for the roots to reach water, and to expand their glorious floury tubers, the higher the chance of growing big potatoes.
The easiest way to grow bigger potatoes is in a raised bed, as the soil will retain a loose structure for years without being compacted, and as long as you properly fertilize the soil with organic matter like garden compost and manure, you can grow potatoes in the same spot year after year if you don’t have enough space for crop rotation.
Use appropriate fertilizers for your tubers
If your potatoes are growing too small, poor soil can be the main cause. Potatoes need high levels of nitrogen, potassium, magnesium, calcium, and phosphorus. They are greedy feeders and can decimate all soil nutrients, so if you don’t practice crop rotation, you NEED to add fertilizers to the soil.
The best way to improve the soil is manure and garden compost which are naturally high in nitrogen and potassium, but crushed eggshells, liquid seaweed and even tomato feed can all be used as part of a regular feeding routine once the leaves start to show.
Before you plant potatoes, it’s important to loosen the soil as the roots grow downwards in the soil, and as the stems grow upwards they produce more roots from the stem. So the soil above and below the seed potato should be loose and rich.
How to space potatoes for bigger tubers
Most bags of seed potatoes suggest planting potatoes about a foot apart, but even the smallest varieties should be planted with a little bit more space than that. While it’s possible to get a crop from a pot by planting three potatoes to a pot, potatoes are best planted two feet apart as a minimum.
Planting potatoes too close together is the most common cause of small potatoes. Potatoes can grow a foot on either side of their tuber in ideal conditions, and when they are planted too close together they will compete for water and nutrients, which limits their size.
Hilling-up Potatoes for bigger crops
Potatoes are often seen as a pretty self-sufficient crop but they are incredibly thirsty and love light.
Potatoes grow their top growth before the tubers begin to form properly, so planting potatoes 6” deep in trenches that are 1ft deep means you have an extra foot of soil to mound up either side of your potato.
This means that the top growth is forced to grow taller and stronger, while the roots start to form from the old leaves underground, creating more potatoes. As you do this, the top growth grows more leaves and generates more sugars and carbohydrates to send down to the developing tubers.
These leaves are under unnatural stress so need easy access to light, and the roots need plenty of water to maintain our constant management. A combination of hilling up in trenches bathed in full sun is perfect – particularly for main crop potatoes.
When to plant potatoes for bigger crops
One factor that new gardeners often report is that their potatoes seem to be growing slowly or erratically. It’s an easy mistake to make, but the variety of potato you grow entirely dictates when you plant it, and when you plan to harvest it.
The guide to this is in their name. Any bag of seed potatoes you buy will be called ‘first early’, ‘early’, or ‘main crop’. While you can plant them at any time of year, main crops planted too early are susceptible to early blight, and first earlies planted too late will suffer in the summer heat as their tops will fail before the tubers are fully formed.
But there’s an easier way to tell the difference between potato types:
- First early potatoes are excellent boiling potatoes, and make brilliant potato salads.
- Early potatoes are perfect for mashed potato, with good water content, but a flouriness that helps them absorb butter for the ultimate mash.
- Main crop potatoes make ideal roast potatoes and baked potatoes as their flesh is lighter and steams itself within the thicker skins.
Here’s our brief guide to how and when to plant and harvest different potato varieties for bigger crops.
When to plant First Early (New) potatoes
First Early Potatoes should be planted out in February or March, as soon as the last frost has passed. A few weeks before the last frost, expose them to light on a windowsill to promote new growth from the seed potatoes, and as soon as they have green shoots appearing, they can be planted in the ground.
First early potatoes benefit most from nitrogen, and some of the fertilizers like calcium are less important. Calcium is for developing healthy skins on potatoes, but as new potatoes are generally thin-skinned watery varieties, it’s more important to promote fast top growth.
Plant them in a trench (at least 6” deep) and as the plants grow, hill them up and feed with liquid seaweed every fortnight. By June/July you’ll be harvesting a healthy crop of small new potatoes. For bigger potatoes, look to the Earlies and Main Crop Potatoes.
When to plant Early (Second Early / New) potatoes
Early Potatoes, sometimes called Second Earlies, are also new potatoes and can be planted at the same time as First Early potatoes, but to avoid the risk of infections and wilting top growth, they are best planted in late March / early April when spring starts to feel warmer, and summer is just around the corner.
Like First Earlies, they want high nitrogen feeds, and a good amount of manure mixed through their planting trenches, but a decent garden compost that includes kitchen waste and eggshells will give them a good boost of calcium and potassium too, which helps them develop slightly thicker skins.
When to plant Main Crop potatoes
Main crop potatoes are the most prolific big potatoes. They have the longest growing season and get started in hotter temperatures – mid to late April – so have more time to grow leaves before they put the energy into the tubers.
Providing them with a well-mixed bed of manure, garden compost and free-draining soil gives them a great start, and hilling them up every two weeks as the top growth gets bigger creates more space for new roots to form.
To feed main crop potatoes, give them liquid seaweed until August to keep leaves and stems healthy, and then stop when day lengths start to shorten, watering generously once a week when it hasn’t rained to allow the tubers to plump up.
What is the best fertilizer for bigger potatoes?
Potatoes need a balanced fertilizer with high Nitrogen, Potassium and Phosphate, but benefit from added calcium and magnesium too. A general-purpose liquid seaweed or vegetable pour-and-feed fertilizer is usually ok, but making your own mix of manure and compost at the start of the season will give them an unbeatable boost.
Can you eat small potatoes?
Small potatoes are fine to eat. They won’t have the same texture as fully developed tubers, but they won’t harm you either. The only time that you shouldn’t eat potatoes is when they are green. Green potatoes can be poisonous and are caused by being exposed to light during the growing season.
Growing bigger potatoes is definitely possible, even if you’re still feeling frustrated at last year’s crop. It’s best to plant potatoes in soil that was used for beans or sweetcorn the previous year, as they add nitrogen back into the soil.
However, if you’re short of space, growing potatoes in old soil, refreshed with manure and compost, and regularly fed through the growing season will give you a plentiful crop next year.
Just remember that you’re not alone, as the world gets warmer we get hotter shorter summers and potatoes simply get confused and can’t keep up with our changing climate, so it’s our job as gardeners to adapt and support our crops.