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General Guidelines*

*This is a compilation of over 2,000 samples tested in our laboratory using the NCSU Porometer. These data are offered as guidelines, NOT STANDARDS, for these substrates. There are no standards; and it is our position that standards for these materials are inappropriate. However, it is useful to have numbers as guides.

The values for total porosity, air space, bulk density, percent moisture, and mass wetness are not averages but those that we expect to see from that particular substrate. The Max/Min values are the total range we have found for that material - not "acceptable" ranges.

Substrate

Total Porosity

Air Space
Bulk Density
Mass Wetness

Median

Max/Min

Median

Max/Min

Median

Median

Vermiculite

78-80

85/74

6 - 10

26/4

0.16-.018

1.5-2.0

Perlite

68

82/65

28-32

46/14

0.15-0.17

1

Bark

75-80

83/73

19-24

41/6

0.2

1.5

Bark Fines

75

78/73

16

20/10

0.25

1.5

Peat

89-94

97/87

20 - 12

27/6

.06-.10

3.0-5.0

Compost (yard waste)

83-87

88/80

7 - 18

44/3

.23-.28

1.0-1.5

Rockwool

90

94/87

20

25/19

0.2

1.0-1.5

Peat:Vermiculite

88

90/82

9

13/6

0.14

2.0-3.0

Peat:Perlite

78

82/76

16

27/14

0.12

1.5-2.5

Sand

38

38/36

3

4/2

1.4

0.1

Mineral Soil

50

-

3

-

1.2

0.05-0.17

Bark:Sand

76

-

10

-

0.46

1.9

3Bark:1Sand: 1Peat

71

-

5

-

0.5

0.45

3Soil: 1Bark

54

-

4

-

1.08

0.14

3Bark: 1Peat

81

-

16

-

0.17

1.58

50 Compost:50 sawdust

86-84

-

13-11

-

0.26

1.25

Bark Ash

80-68

-

21-5

-

0.10-.038

0.56-4.01

Commercial Peatlite Mixes

87

90/84

9

13/9

0.14

2.5

Retail Mixes

82-86

89/77

9 - 12

17/3

0.10-4.0

1-2.5


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