Potatoes grow under the soil – this means it’s not convenient to look at them to see when they’re ready to harvest until you actually harvest them. This is not an issue if you have a full garden or field of them. But it can be an issue if you have only one or two plants and you dig them up and they’re not ready. There is another way – looking at the potato plant/leaves will tell you if the potatoes are ready. I will explain how in this article.
Identifying the stages of potato plant growth
There are various stages a potato plant goes through before it has finished its growth, these are:
- Potato plant emerging through the soil
- Small plant 1 foot or 30cm high
- Medium-sized plant 2 feet or 60cm high
- Fully grown plant 3 feet or 90cm high
- Fully grown plant with flowers
- Flowers die-off tall plant
- Potato tops shrink in height down to 2 feet 60cm lose bright green colour – patches of yellow-leaved plants in the crop.
- Potato plants turn yellow leaves blacken tops lying on the soil
- All potato plants leaves fall off and the stems blacken
- All colour is gone from the tops – just white fragile stems remain.
What a potato plant looks like when its nearly ready to harvest
I know my potatoes are becoming ready for harvesting when these final stages begin to happen. First the flowers show on the plant – this is the beginning of the potatoes becoming ready.
The potato plant can have flowers showing for a few weeks during this time there will be potatoes but they will be small. All the leaves will usually be green during this time
The next stage is the flowers dying off the plant and the tops begin to shrink back down to the soil. There will be a few plants starting to turn yellow – this is the beginning of the potato plant dying. The potatoes will be more or less ready to eat at this stage.
If all the plants are healthy and you have blight under control you should allow the plant to mature to the final stage.
The final stage of the potato plant growth is when the the leaves have died from the plant and only the stems are left lying on the soil. This is when your potatoes are fully ready to harvest.
Harvesting early or new potatoes
There is an exception to the rule of waiting until the potato tops change colour and die back. Early potatoes varieties or new potatoes are usually dug when the tops are green and the potatoes are big enough to eat.
If you have enough early potatoes you can just dig what you need and allow the remainder of your potatoes to mature. Never dig more early potatoes than you need. The plant hasn’t matured enough to allow the skin to set and thicken. This means the potatoes will go stale and soft quickly -within 5 days from digging.
Important points to remember about changes in potato plant colour
There are times when your potato plant will change colour and it is not ready to harvest.
If the plant changes colour before it has flowered then you may have an issue with nutrients, water or whichever sprays you have applied. See article- Why are my potatoes plants turning yellow for more on this.
Diseases and pests
It may be that your plant has been infected with potato aphids or blight to make it change colour. It will be obvious if it is not natural crop senescence (dying). If these changes happen before flowering you should investigate further.
The thing to remember is that if it has flowered and its coming near the end of natural growth the whole plant will turn yellow and die back slowly.
If it is potato blight the whole plant will turn black quickly -within a couple of days. Much quicker than the slow yellowing of natural healthy dying.
The main thing you’ll notice if your crop has an infestation of potato aphids is that the leaves will all curl tightly on the plant. It will dramatically stunt the plant’s growth – the plant will remain green in colour.
Dont rush to dig all your potato plants at the first sign of one potato plant turning from green to yellow. Dig the soil from around the side of the plant and inspect the size of the potatoes before you pull or dig it up. Once you remove a potato from the stem of the plant it will not grow anymore.
- For early potatoes wait at least until all the flowers have gone from all of the potato tops.
- For main crop potatoes It’s better to wait until all the leaves and stems have turned yellow or brown. They should have fully died back and are laying flat on the soil.
When potato plants get time to mature naturally the potatoes are much tastier- try it and see!