7 Steps to Growing Potatoes Under Black Plastic
Potatoes like growing where it is dark and warm. They also need plenty of moisture to produce juicy tubers. Black plastic creates a perfect environment for growing potatoes. The traditional methods of growing potatoes involve lots of digging, weeding, and hilling throughout the growing season, and a black plastic mulch will eliminate many of these chores.
To grow potatoes under black plastic, make sure the plastic is well anchored on all sides to keep it from blowing away. Cut x-shaped slits in the plastic at the desired spacing, and plant your potatoes about 15cm (6 inches) deep. At harvest time, pull up the black plastic sheet and pick up the tubers.
Black plastic mulch for potatoes has a lot of advantages, but there are a few things to watch out for. Following the steps below should help you have a productive potato harvest using “plasticulture”.
How To Grow Potatoes Under Black Plastic Mulch
If you have decided to give black plastic mulch for your potatoes a try, here are a few simple steps to set everything up to have a successful year.
- Prepare the seedbed
- Lay down the plastic
- Anchor it well!
- Cut holes for the potatoes
- Care throughout the summer
1. Prepare The Seedbed
Prepare your plot as you normally would for potatoes. The only difference is you do not have to dig a trench or holes for the seed potatoes. They will be planted later right under the plastic.
2. Lay Down the Plastic
Roll out your black plastic sheet. The plastic usually comes in rolls of varying widths and lengths. They are typically available in 1m or 2m (3ft or 6ft) widths and can be anywhere from 30m to 150m long (100ft-500ft). Which width you choose depends on how you want to space your potatoes. Typically potato rows are spaced about 60cm to 90cm apart (2ft-3ft). If you get a 1m wide sheet you can plant a single row of potatoes on it, whereas a 2m sheet would be wide enough for two rows of potatoes.
Black plastic also comes in rolls about 3m wide (10ft). This can be beneficial if you want to cover a large area of your garden. But bear in mind that the larger the area covered, the less water that will reach your soil, and your garden might dry out.
If you are laying several sheets of black plastic beside each other, it is best to leave a space between the sheets so water will be able to run off into the soil.
3. Anchor It Well!
This is a very important step to do well. Don’t skimp on anchoring your plastic or you will be cursing yourself when the first storm blows through.
The most secure way to anchor the plastic is to dig a shallow trench (about 15cm) deep along each side of the plastic sheet. Tuck the plastic into the trench and then back fill the dirt into the trench so the sides of the plastic are all buried.
Don’t make the plastic sheet too taught or it is more likely to tear. But don’t make it too floppy either!
4. Cut Holes For The Potatoes
Now it is time to cut holes in the plastic for your potatoes.
Start at one end of your black plastic where you want the first potato plant to be, and cut an “X” the sheet by making two 15cm (6inch) cuts. Fold the little flaps under the sheet so they will be out of the way. Move along the plastic sheet, making additional cuts every 30cm (1ft) or so, and fold the flaps under as you go.
In each hole that you cut, dig a small hole about 15cm deep. Plant your seed potatoes and cover them back up.
Removing puddlesAfter you plant your potatoes, it is a good idea to water the whole area thoroughly. Wherever a puddle has formed on the black plastic, poke a small hole and let the water drain out. This will keep water from pooling in these low spots when it rains, and will help keep the soil underneath moist.
6. Care Throughout the Summer
There is very little maintenance that needs to be done throughout the summer. Make sure you monitor the temperature and moisture level under the black plastic and adjust as needed, and you might need to pull a few weeds that spring up in the holes you cut. Other than that, it should be smooth sailing until fall.
Harvest is always a great time of year. It is even better when you don’t have to work for it. Instead of being buried under a pile of dirt, the potatoes will grow under the black plastic sheet. Simple roll up the sheet and the potatoes will be right near the surface.
Advantages Of Black Plastic Mulch
Black plastic mulch will warm the top few centimeters of soil by about 5C by absorbing sunlight. This can greatly extend on your growing season by letting you get your crops in the ground earlier than normal. Potatoes grow best with a soil temperature of around 20C (68F), so the warmer soil really helps them at the beginning and as the weather cools off in the fall.
Like all mulch, black plastic holds moisture in the soil. This is very important for good tuber development (potatoes contain a lot of water), especially during the high heat of summer. Black plastic mulch is a great tool to aid with water conservation. Though they are more expensive, semi-permeable rolls of black plastic are available that allow water to seep through to the soil below.
For many people, the best part of black plastic mulch is that it chokes out weeds and all but eliminates this necessary, and sometimes unpleasant, garden chore. As with any crop, potatoes will produce poorly when competing with weeds. Black plastic is particularly helpful if you won’t have enough time to properly weed the plot, and it gives you more time to weed somewhere else!
When it comes time to harvest, your potatoes will mostly be lying on the ground under the black plastic. They are just waiting for you to roll up the sheet and pick them up.
Disadvantages Of Black Plastic Mulch
Yes, the heat can be a disadvantage, too. If not properly monitored in the hot, dry summer, the heat can get so high that it can be detrimental to the living things underneath. While it kills off the weeds, it can also remove a lot of the beneficial aspects of the soil, and the soil can become compacted and “dead” looking. The heat can kill off beneficial microorganisms and bacteria, and it can also get so warm that it chases earthworms away.
On the flip side, it can create a warm, damp environment perfect for the gardener’s favorite: the slug. Closely monitor under your tarp to make sure these creatures are not invading. Putting up slug traps or other deterrents might be necessary. If slugs are a problem in your area, it is a good idea to do this when you first install your black plastic before the slugs have a chance to take over.
The biggest down side of black plastic mulch is that it is not eco-friendly. Besides the environmental impact of creating the plastic, most plastic mulch can only be used once so it creates a lot of waste every year. There are some situations where black plastic is the best option, but it must be carefully considered if it should be used as a long term practice.
There are biodegradable options available, but they are hard to come by and are often cost-prohibitive to purchase year after year.
If you live in a very windy area, any type of plastic mulch might not be the best idea. There is nothing so frustrating as seeing your carefully laid sheets flapping in the wind, or blowing away across the field.
Black plastic sheeting is definitely not the most beautiful thing to look at. However, sometimes a smooth sheet of plastic looks better than an unruly patch of weeds. And sometimes you have to choose practicality over beauty.
Clear VS Black
Clear plastic will raise the temperature of the soil even more than black plastic by the greenhouse effect (basically it creates a mini greenhouse right on the ground, where the heat from the sun comes in but can get back out). However, clear plastic does not choke out weeds. In fact, it can actually make the weeds grow faster by creating a perfectly warm and moist environment. Even so, there are some instances where clear plastic is the way to go…but not for your potato plot.