Free herb pot soil calculator. Enter how many herb pots you are filling to find the soil in litres and the 10 litre bags you need.
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Enter how many herb pots you are filling. This calculator allows 3 litres of soil per herb pot, and divides the total by 10 litres per bag to give the bag count.
Soil litres per pot herbs in this calculator is 3 litres per herb pot, a mid size pot average. Small herb pots need less and large pots need more, so use this figure for planning a typical herb collection, and adjust for very small or very large pots using the size table below. For 10 pots, this calculator gives 30 litres of soil and 3.0 bags of 10 litres. For 4 pots, it gives 12 litres and 1.2 bags, meaning 2 bags bought in practice, with soil left over.
A herb pot size litres table helps you check the 3 litre average. A 10 centimetre pot holds about 0.5 litres, a 15 centimetre pot about 1.9 litres, a 20 centimetre pot about 4.5 litres, a 25 centimetre pot about 8 litres, a 30 centimetre pot about 13.5 litres, and a 42 centimetre pot about 28 litres. These are standard pot volumes, and tapered pots hold a little less than straight sided pots of the same diameter. Measure the top diameter and the depth, since two pots with the same diameter but different depths hold very different amounts.
Herb types need different pot sizes, even though this calculator plans 3 litres per pot on average. Basil and mint grow fast and suit pots of 20 centimetres or more, with mint always in its own pot, since it spreads aggressively. Rosemary and lavender suit larger, well drained pots and hate wet soil. Thyme, oregano, and chives suit smaller pots of 15 to 20 centimetres. Parsley and coriander suit medium pots and regular watering, since they wilt fast in small pots.
Herb soil mix ratio for containers is lighter and freer draining than garden soil. A good herb mix is about 50 percent potting mix, 25 percent compost, 15 percent perlite or coarse sand, and 10 percent coco peat, which drains well while holding some moisture. Another herb mix is 35 percent coco peat, 35 percent vermicompost, 20 percent garden soil, and 10 percent perlite. For Mediterranean herbs such as rosemary, thyme, and lavender, add extra perlite or grit for drainage. For leafy herbs such as basil, parsley, and coriander, add a little more compost for moisture.
Potting soil vs garden soil pots is an important choice: use potting mix in containers, not garden soil. Garden soil compacts in pots, drains poorly, and can carry pests and weed seeds. Potting mix is light, drains freely, and holds air around the roots, which herbs need. Topsoil and garden soil suit raised beds, where drainage and structure differ. Never fill a herb pot with pure garden soil, and never use pure compost either, since it holds too much water and settles heavily.
Herb pot drainage starts with holes in the base and a free draining mix, not a layer of gravel, which actually raises the water table inside the pot. Herb pot fill gap means leaving 1 to 1.5 inches, about 2 to 4 centimetres, below the rim, so watering does not overflow and soil does not wash out. Fill the pot to the fill gap, firm the mix gently, water it in, and top up if it sinks. Do not fill a container completely to the rim, since the first watering will spill soil everywhere.
Herb pot settling allowance is the extra soil you need because fresh mix settles after watering. Allow 5 to 15 percent extra, most commonly 10 percent, on top of the calculated volume. For 10 pots at 3 litres each, the calculated total is 30 litres, and with a 10 percent settling allowance, buy about 33 litres, or 4 bags of 10 litres in practice. How many bags soil herb pots need in whole bags is always rounded up: a result of 1.2 bags means buy 2 bags, and a result of 3.0 bags means buy exactly 3 bags, plus one spare for topping up later.
Herb pot soil cubic feet quarts conversions help when bag labels use different units. One litre is about 0.035 cubic feet and about 1.06 quarts. Three litres per pot is about 0.106 cubic feet and about 3.17 quarts per pot. Ten pots at 30 litres is about 1.06 cubic feet and about 31.7 quarts. A 25 litre bag is about 0.88 cubic feet, a 50 litre bag is about 1.77 cubic feet, and a 10 litre bag is about 0.35 cubic feet. Always check whether the bag label gives loose volume or compressed volume, since compressed bags expand when opened.
You can reuse old potting soil for herbs if you refresh it, but do not reuse it unchanged year after year. Old mix compacts, loses nutrients, and can carry disease from last season. To reuse it, remove old roots, mix in fresh compost and perlite at about one third fresh material, and feed the herbs during the season. Replace the mix completely every 1 to 2 years for herbs, and always use fresh mix for seedlings and for herbs that struggled last year.
About 3 litres per herb pot in this calculator, a mid size pot average. Small pots need about 0.5 to 1.9 litres, and large pots need 8 litres or more.
Divide total litres by 10 litres per bag, then round up to whole bags. Ten pots need 30 litres, or 3.0 bags, and 4 pots need 12 litres, or 1.2 bags, so buy 2 bags in practice.
Basil and mint suit pots of 20 centimetres or more, with mint in its own pot. Rosemary suits a larger, well drained pot. Thyme, oregano, and chives suit 15 to 20 centimetre pots.
About 50 percent potting mix, 25 percent compost, 15 percent perlite or coarse sand, and 10 percent coco peat. Add extra grit for rosemary, thyme, and lavender.
No. Garden soil compacts in pots and drains poorly. Use potting mix in containers, and keep garden soil for raised beds.
Leave 1 to 1.5 inches, about 2 to 4 centimetres, below the rim, so watering does not overflow and soil does not wash out.
Yes. Allow 5 to 15 percent extra, most commonly 10 percent, because fresh mix settles after watering. For 10 pots, buy about 33 litres instead of exactly 30 litres.
One cubic foot is about 28.3 litres, and one litre is about 0.035 cubic feet and about 1.06 quarts. Three litres per pot is about 0.106 cubic feet.
Yes, if you refresh it with about one third fresh compost and perlite, and replace it completely every 1 to 2 years. Use fresh mix for seedlings.
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