Wasilla Alaska Garden Adventures

Wasilla Alaska Garden Adventures - learning about gardening up north.

Wednesday, April 13, 2016

Soilless Grow Mix for Alaska Grow Buckets

You can buy commercial grow mix usually in large 3.8 Cubic ft. bales made from Sphagnum peat, lime, perlite, and vermiculite or you can mix your own. You can usually find commercial grow mix at Home Depot or Lowe's Home Centers and many local garden centers. The brand is not important, just check the label for ingredients. One large bale should fill six Alaska Grow Buckets.

Sphagnum peat moss is a stable organic material that holds 15 to 30 times its weight in water and decomposes very slowly. It contains about 1% N but little is released because it breaks down so slowly. It has a pH of about 4 so lime must be added to the mix with sphagnum peat, at the rate of 8.5 lb. per cubic yard of peat to neutralize the acidity.

Coco Coir comes from coconut husks and is a waste product of the coco fiber industry. It has physical properties much like peat but a higher pH of about 6. It holds up to nine times its weight in water. It can have a high salt content. It comes in compressed blocks that must be soaked in water for several hours or overnight before mixing with other ingredients.

Limestone is either calcitic (high calcium) or dolomitic (high magnesium; both are used to increase the pH of a mix but dolomite lime is preferable for supplying both Ca and Mg.

Vermiculite helps hold water and fertilizer in the potting mix, and it also contains some calcium and magnesium. It has a pH near neutral. Vermiculite comes in different grades; medium grade is usually used for starting seeds, a coarse grade may be used for larger plants.

Perlite is a volcanic rock that has been heated and expanded. It is lightweight, sterile and has a neutral pH. It can be used to reduce the weight of a potting mix and increase its aeration and drainage.

Mycorrhizae Fungi colonize the root system of a host plant, providing increased water and nutrient absorption capabilities while the plant provides the fungus with carbohydrates formed from photosynthesis.

Most commercial grow mixes have the proper ratio of ingredients plus wetting agents and may contain Mycorrhizae Fungi and fertilizer - check package label for ingredients.

DIY Grow Mix Recipe:

Bucket = 5 Gallon Bucket to measure.

3 Buckets Sphagnum peat + 1 cup dolomitic Lime
3 Buckets of damp Coco coir pre-soaked in water (follow pkg instruction)

Mixed with
1.5 Buckets Perlite
1.5 Buckets vermiculite

This should make enough to fill six Alaska Grow Buckets. You can also add your own Mycorrhizae Fungi and a slow release organic fertilizer at planting time.


  1. Thanks so much for sharing this awesome info! I am looking forward to see more posts by you!
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