Knowing when to stop watering potatoes before harvesting is an important aspect of successfully growing a healthy potato crop. Proper water management, especially towards the end of the potato growing season, can help maximize potato yield and quality. In this article, we'll take a detailed look at when and why you should stop watering potatoes prior to harvest.
Why Stop Watering Potatoes Before Harvest
There are a few key reasons why it is recommended to stop watering potatoes 2-3 weeks before harvesting them:
Promote Skin Set
It is important for potato skins to properly "set" and thicken before harvest. If tubers are still expanding rapidly with excess moisture late in the season, skins may split or remain thin and tender. Stopping irrigation allows skins to set and toughen up, which helps improve storage life.
Encourage Tuber Maturity
Excess soil moisture late in the growing season can delay natural tuber maturity processes. Discontinuing watering 2-3 weeks before harvest curbs excess vegetation growth and signals to the potatoes that it's time to finish bulking up. This results in more uniform maturity.
Avoid Secondary Growth
With ample late-season moisture, potatoes may experience secondary growth, where tubers start sending out new stolons and producing additional small, immature potatoes. Skipping those last few irrigations minimizes this undesirable secondary growth.
Improve Harvest Conditions
Drier soil makes for easier and more efficient potato harvesting. Digging equipment moves through soil more smoothly without clumping when soil moisture is reduced. Wet, muddy harvest conditions lead to more bruised or damaged tubers.
Reduce Storage Rot Risk
Wet tubers are more prone to storage rot issues like bacterial soft rot. Letting the soil dry out before digging minimizes tuber moisture content and related post-harvest diseases. This is especially important for potatoes going into storage.
Determining When to Stop Watering
Timing on when to stop watering potatoes will vary based on your climate, soil type and other factors. Some general guidelines:
- 2-3 weeks before harvest - This is a good rule of thumb for when to cut off irrigation. The exact number of days will depend on weather and soil moisture.
- When tubers reach desired size - If it's easy to monitor tuber growth, discontinue watering around the time they stop actively bulking up and reach marketable size.
- When vines start dying back - As vines naturally start to yellow and die back, this signals the potatoes are nearing maturity. Time to stop watering.
- When skins are resistant to rubbing - Test dig a plant and rub a potato skin with your finger. If the skin remains intact, it's a sign skins have hardened off, so plants no longer need irrigation.
- Moisture monitoring - With soil moisture sensors, stop watering when the soil drops below 70% of field capacity moisture.
Pay close attention in the weeks before harvest and reduce irrigation frequency gradually rather than abruptly stopping. This allows the potatoes to harden off and finish maturing evenly.
Impacts of Excess Late Watering
It's clear that stopping watering at the right time is important, but what are the potential impacts if you don't? Here are some issues that can arise from excess irrigation right before potato harvest:
- Poor skin set leading to peeling, scuffing, and bruising
- Delayed or uneven tuber maturity
- More small secondary tubers
- Higher disease pressure in storage from soft rot bacteria
- Reduced storability and shelf life
- Excess vine growth at the expense of tubers
- Difficult muddy harvest conditions that damage tubers
- Tubers with higher moisture content and poorer processing quality
- Potential tuber rot during curing if piled wet
While potatoes are tolerant of water, excess moisture right before harvest can lower yield quality and storability. Following the best practices of when to cut off irrigation reduces these risks.
Varieties and Growing Conditions
The ideal timing for stopping watering potatoes will vary some based on the variety you're growing and your regional growing conditions.
- Early season varieties - May need irrigation cut off around 3 weeks before harvest since they bulk up quickly.
- Mid and late season varieties - Are in the ground longer, so may only need water turned off 2 weeks pre-harvest.
- Storage varieties - Ideally stop watering 2-3 weeks out to help maximize their storability.
- Table and fresh use varieties - Don't need to dry out as long before harvest since they're eaten right away.
- Hot climates - Will dry out soils faster, so base irrigation more on soil moisture than days before harvest.
- Cool summer climates - Can potentially water a little longer before harvest since soils stay moist.
- Sandy soils - Drain faster and will dry out sooner than clay soils when watering is stopped.
- High rainfall - May need to stop watering earlier, 4+ weeks out, if heavy late rains are expected.
- Irrigation method - Overhead irrigation wets surface more, so drip or sub-surface may allow stopping water a bit later.
Consider your variety's maturation time and typical soil moisture conditions before harvest to customize when to cut off irrigation.
Stopping potato irrigation at the right time is a balancing act - you want to avoid water stress that reduces yields, but also need to limit excess moisture for best harvest and storage quality. Following the general guidelines of ceasing watering 2-3 weeks before harvesting potatoes ensures tubers harden off properly, mature evenly, and avoid issues like secondary growth, diseases, and bruising. Adapting your specific timing based on potato variety, climate, and soil factors will provide optimal results. Proper late-season irrigation management takes some patience, but pays off with maximized potato crop yield and storability.
Frequently Asked Questions
1. What if potatoes are behind schedule when 2 weeks pre-harvest arrives?
It's better to follow the condition of the crop rather than a date on the calendar. If tubers are still small 2 weeks before the planned harvest date, continue watering until the potatoes size up, skins set, and vines start dying back.
2. How much yield loss can occur from stopping water too early?
If irrigation is cut off 4+ weeks before harvest, it's possible to see a 25% or more reduction in total yield depending on soil type and weather as plants are stressed. Losses are minimized by gradual reduction in watering over 2-3 weeks.
3. What are signs tubers have started maturing?
Indicators potatoes are starting the maturation process include vines yellowing or falling over, skins resisting rubbing, and tubers resisting thumb pressure when tested. These are signs to stop irrigating.
4. Should all potato varieties be treated the same before harvest?
While the 2-3 week guideline fits most types, very early potatoes or thin-skinned new potatoes may do best with irrigation ending 10-14 days before harvest. Long-season or storage varieties need a full 2-3 weeks dry down.
5. How dry should the soil be at harvest?
It's ideal if the soil is moist but not wet and muddy at harvest.Aim for around 50-70% of field capacity moisture in the soil when digging potatoes.