How To Set Up a Sheet Mulch/Lasagne Garden + Cold Frame Setup for Season Extension

A cold frame is a sort of mini greenhouse used extend the growing season. A sheet mulch is a style of no-till garden bed preparation where layers of different types of organic matter and soil amendments are placed on top of the existing  ground. Here at Greenshire we decided to combine the two ideas and see how it works out.

Using the permaculture principle of turning waste into resource we rescued some old windows and scrap  from going to the dump, in order to make the cold frames. We chose to sheet mulch the growing bed inside the cold frame because there are  electrical wires running underground somewhere in the area where the frame was to be placed.

Here’s the step by step instruction of how we made our sheet mulch cold frame which will allow us to extend our growing season by several weeks….

STEP 1

The wood is cut to fit the length and width of the window, and the desired height of the frame. Generally the height is 6-10 inches at the north wall, and a few inches shorter at the south wall. Then nail each side together to complete the cold frame base.

STEP 2

The cold frame base is placed in the general area we wanted, and then a compass is used to orient the frame so that its length runs east-west. The  footprint of the frame base is marked out the with small pieces of wood with bricks on top of the corners to keep them from going out of place, and the frame base is then set aside.

 

STEP 3

The sod is removed inside the marked area and the frame base is put back around the growing area. This step might not have been necessary but it was done to make it easier for plant roots to penetrate through to the deeper soil. Sheet mulches can be very successful without doing any sod or weed removal. Pieces of sod were used as props to make the frame base exactly level. The grow bed was also eventually made to be level.

 

STEP 4

Coffee grounds (leftovers from making coffee) and torn up filters are placed on top of the exposed soil at about 1/2 inch-1 inch thick. The grounds are thoroughly soaked.

STEP 5

Leaves are placed on top of the coffee grounds 4-6 inches thick. You can go up to 8-10 inches if you have the allowable depth inside the frame. Remember that this layer will compress quickly. If possible, it’s best to chop the leaves up by running a lawnmower over them or putting them through a shredder. The smaller the pieces, the quicker they will break down, and the easier the plant root penetration. The leaves are thoroughly soaked.

STEP 6

Soil mixed with coffee grounds at a 2 to 1 ratio is placed on top of the leaves and then soaked after raking it level. You should have a minimum of 4 inches of ‘head room’ from the finished soil surface to the top edge of the cold frame where the glass will be. This is of course to allow room for your plants to grow. 4-6 inches is suitable for growing baby salad greens or starting seedlings. Remember that your sheet mulch will eventually compress and sink down a bit, possibly a lot but it may not happen before your first harvest/removal of seedlings.

 

STEP 7

Place the window on the frame and bank soil against all four sides of the base, right up to the top. This will help regulate the temperature inside the cold frame. Hay or straw can be added on top of the soil add further insulation.

Some people use semi-composted manure instead of soil because as it decomposes, the manure will give off heat, which could significantly increase the temperature inside the cold frame. The possible drawback is that it could contaminate the growing medium inside the frame with e coli bacteria or other harmful fecal coliform bacteria.

 

STEP 8

If possible, test the air and soil temperatures inside the covered frame before planting. The soil temp can be tested using a meat thermometer. When testing the air temp, be sure to get readings at night, as well as the warmest parts of daytime. This will give you a sense of the range of temperatures inside the cold frame. The range you need will depend on what you’re growing of course. It is advisable to attach your window to the frame base with hinges for easy opening. Whether opened or closed be careful to have the window weighed down so that wind doesn’t blow it around, possibly breaking the glass.

There are automatic window openers that are hinges you can buy which have a temperature sensitive gas chamber that (as the name says) opens or closes the window automatically. My understanding is that these are made with plants temperature needs in mind. I bought mine from Lee Valley, as it was the only source I could find. Well worth the investment in my mind, as with no auto-opener, I’ve had plants bake to death inside cold frame under full sun.

 

STEP 9

Assuming your temperatures are adequate the frame is now ready for planting. A light layer of mulch may be applied as well if you want to conserve moisture and insulate from cold air, though it may be beneficial to leave the soil bare, as the dark colour of the soil will absorb heat from the sun.

 

WHEN TO PLANT

There are too many variables to consider for me to give a one-size-fits-all recommendation. Do as much research as possible on the coldest soil and air temperatures that your chosen plants can withstand

In spring, the most important thing will be the soil temperature, because if you plant too early in the spring your seeds may rot in the wet spring soil waiting for warm enough conditions to germinate.

When planting in the fall…Keep in mind that once winter hits your plants won’t be growing very much due to the colder temperatures and lack of  sunlight. So you need to give enough time to get to maturity while temperatures are still mild and daylight hours are still relatively long. That being said, starting your plants too early may result in your plants bolting to seed prematurely. This happens to some plants (eg. radish, spinach, bok choi etc.) when they experience too much variation between warm and cold temperatures. This timing varies greatly from region to region so I can’t really give a recommendation that would work for everyone but generally in my hardiness zone (zone 5) if you plant in mid september your plants will be mature by November, and you’ll have missed the big temperature swings. I say this but the last few years have seen increasingly extreme variations in temperature, with summer weather lasting much longer than usual, and   20°C + weather sneaking in as late as the end of September and even October! Don’t let this keep you from trying your hand at growing in a cold frame. It can be pretty amazing to be growing and harvesting fresh vegetables in the snow!

 

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