Plastic Lined Garden Beds

Our well produces very little water so I am always looking for ways to conserve water and/or grow plants that do not require irrigation. Our soil is very free draining with silt on top scattered gravel and 2-12 inch rocks in the top 2 feet, and more rocks and gravel deeper down. Water just drains away into the ground and is then unusable for plants on the surface. Drip irrigation helps and watering shorter but more frequently is better for this type of soil. This year I am watering my in ground tomatoes (which are drought tolerant in their own right) with ½ gallon per hour drippers for 10 minutes 4 times a day.

For several years now we have gotten no stone fruit, including cherries, apricots, and plums though if all of those fail sometimes we get peaches and nectarines. In 2022 the snow drift was so deep 10 trees were broken till the main trunks were Z shaped. Apples usually produce fruit and we got some asian pears last year, but the bartlet pear tree and granny smith apple got fire blight. There was no fruit at all in 2024 so I cut off the water to all the stone fruits, the fire blight affected apple and pear, and 2 rows of rhubarb in the lower garden. Also I didn't plant the lower drip irrigated garden and consolodated the best raspberries and best thornless blackberries in plastic lined beds.

I first tried plastic lined beds in 2022 with the idea that it would reduce water infiltration into the soil but was concerned it would lead to a buildup of salts. Added water is high in CaCO3 and I add fertilizer. The water evaporates leaving behind the salts, sometimes this is visible on top of the soil near the edges of the beds as a white powder. I could not find much if anything online where anyone had tried this before. First I lined 2ft x 2ft holes partially with plastic and planted honeyberries and gooseberries with 2 drippers per location. Some moss grew on top of the soil and it seemed like there was too much water so I used a long metal rod to poke some holes in the plastic. It is now 2024 and the honeyberries are doing fantastic (about 6 cups of berries per plant) but the Hinomaki Yellow Gooseberry wasn't doing well and the ones I tried were really good so I had to move it.

In spring 2023 we dug out one of the 32 inches wide and 30 ft long raspberry beds 2 feet deep, lined it with black construction plastic, removed the rocks, added fertilizer, and planted rhubarb, raspberries, and strawberries. The bed has a single drip line and the plants did fantastic the first year and the Joan J raspberry plants produced the largest raspberries I have every grown. By July, 2024 (the next year) the rhubarb was not doing well and some of the raspberries are dry. It was very hot, the bed looked dry, and the drip was not enough. Most but not of the rhubarb went dormant. Hand watering helped the raspberries some, but it particularly helped the strawberries which seem more salt tolerant than raspberries.

In spring 2024 we dug out the other raspberry bed 36 inches wide and 30 ft long 24-36" deep deep, and again removed the rocks and added fertilizer. I planted a double row of fig trees and planted blackberries and chilies. Removing rocks takes a long time and I needed to plant another 50 figs so tilled the old 40 foot blackberry bed and planted those figs a week later. The figs in the plastic lined bed developed much faster and started fruiting, and the blackberries spread under the figs making a deep green mat. The chilies produced more than we could use. I tried adding more water and fertilizer to the un-lined tilled bed but the fig trees still lagged far behind. Both beds have a single line of drippers and because the drip line doesn't cover the whole width of the row both get supplemental hand watering as needed. Still the plastic lined bed is much better than the non-plastic lined bed. Blackberries and figs are both tolerant of salt and high pH so I am hoping the plants will do well indefinitely. While I have had poor results co-planting in the past it seems figs trees companion well with short plants like creeping blackberry, strawberries, or ground cherries. Upright blackberries and some types of chile plants (cayanne) are too tall and will shade small fig trees.

The Technique of Plastic Lined Garden Beds

We first dig out a bed 3 feet wide 2½ - 3 feet deep with a backhoe, remove sharp rocks at the bottom, and line it with black construction plastic. A 10 x 100ft roll is about $70 and it takes about 38 feet to do a 30ft bed. We then use a 1" wire mesh sieve to separate out the bulk of the rocks, replace the soil, and add field silt to make up for the rocks and gravel that were removed. Big rocks are placed around the bed as a decorative border and used to hold down tarps to protect fig trees in winter.

Ideas For Improving Plastic Lined Garden Beds

This could be improved! Ideally a heavier grade of plastic (pool liner maybe) would be more durable. Salt build up over multiple seasons could be reduced by burying perforated pipes the length of the bed, run out through the liner at the bottom, and drained down the hill by gravity. During spring thaw and rains while plants are still dormant open the valve to release water with built up salts, and then close the valve to conserve water during the growing season. If using raised beds this would be even easier to setup!

In spring 2024 we did the second raspberry bed but made it 3 feet wide and to 30 inches deep on most places. We planted figs and some of the best thornless blackberries we didn't want to loose, and chilies. The figs are getting huge and look super healthy and the blackberries are better than I have ever seen them, and I have more chiles than I can eat. Some wonderberries, physalis pruinosa, and tomatillos also came up and they all look fantastic. Fig trees have a high tolerance for salt and alkaline soils so they may do perfecty well in a plastic lined bed for many years. It was so much work sorting the rocks on the first bed that when we did another 40 foot bed we just tilled it and removed the weeds (this had been dug before and some soil replaced with hypnum peat). We planted figs and corn in this bed all about a week after the first plastic lined bed. The plants in this bed do not look nearly as good, though it is hard to compare since it was not planted at exactly the same time.

Do you think this will work or will salt be a problem?
Do you think the piping idea will solve the salt problem?
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