Potting mixes are not all the same!
There are a lot of potting mixes on the market. Some are good but expensive, others cheap but very poor quality and best not used as they can be quite toxic to the plant roots and burn the white root tips (the growing parts that take in water and nutrients).
Good potting mixes are composted for about two months to leach out the toxic tannins in the pine bark or sawdust that almost all potting mixes are made from. The dark colour is mainly from the composting operation but can be produced just by applying some Ferrous Sulphate that will blacken the sawdust. This is done with really cheap potting mix that may be only 2 to 3 days old but this is still raw even though it looks mature. This super cheap mix will still be very toxic to your plants!!!
To improve and make maximum use of your Compot you can add some of the composted material from your Compot to your potting mix. This will be moist and partly composted and will increase the volume of your potting mix at no extra cost. Any extra material will need to be well mixed throughout your mix so that there are no areas that have lumps of one type of ingredients that might cause large air spaces which can lead to some roots drying and dying so the plant won’t thrive.
If you want to make your own seedling potting mix, instead of buying the more expensive bags of special seedling mix, all you need to do is sieve your existing mix and use the ‘fines’ that drop out of the sieve.
These ‘fines’ can be caught on a piece of plastic sheeting and then tipped into the seedling tray ready for you to plant your seedlings. The larger bits left in the sieve can be mixed into your normal potting mix. Some plastic sheeting is useful to have on your potting up bench as then any mix that falls while potting up is caught, kept clean and easy to tip back into your pot, so you do not lose any mix and also keep your potting up bench clean.
Click to view BOB re-potting Dendrobium
Cheap potting mix does not have any (or very little) extra fertiliser added to it, but Premium mixes must by law have enough fertiliser added to be active for the next three months. You can buy cheap potting mix, add some slow release fertiliser, eg Osmacoat, Nutricoat etc. Mix it in well and then you have a “premium mix” at a cheap price.
Any added fertiliser in addition to any you may have incorporated into the mix, needs to be applied to the TOP of the pot. The action of water, be it from rain or watering, will move the liquefied fertiliser DOWN with it, NOT up NOR sideways. A lot of people are advised to place the fertiliser in the bottom of the pot but all that does is lets the water take the fertiliser out of the bottom of the pot away from the plant roots. ie. of no benefit to the plant but a lot of profit to the fertiliser manufacturer.
Today’s Did You Know…?
Most people think of Orchids as those plants with big purple flowers often used in a bride’s wedding bouquet or in an expensive flower arrangement.
Orchids come in a wide range of colours (including spots and stripes) and a very wide range of sizes. Some Orchid plants are up to 5 m tall, down to ones that are only a few centimetres tall. Most grow above the ground but a few Australian native Orchids grow entirely underground in caves in the deserts of central Australia.
Some of the flowers are a single flower up to about 15 cm wide while others are only half a cm. wide. Some plants have multiple branches with a lot of flowers on each branch while others are just a single flower.
Some orchids are grown with NO potting mix at all, just an open container with the plant roots hanging down over pools of water underneath them. The water creates high humidity around the roots. It is only the Vanda type orchid that is grown this way.
In Thailand large commercial growers of Vanda type orchids grow 1000’s of plants for daily supply to the Bangkok flower markets as cut flowers. A truly amazing sight to see.