I had a question posed to me through a comment on this blog that I've not really written about dealing with plant propagation: Why do I use sand instead of soil for cuttings?
Before I answer let me say that most (maybe about 95%) of my successful cuttings were done in sand alone with the rest in either in a sand and peat mix, regular soil, or water. There is no wrong way to root a cutting as long as it produces a healthy plant. If you like rooting cuttings in a jar of water then by all means go for it! There's more than one way to skin a cat (or so I've been told, I'd never do such a thing!)
I use sand for a several reasons:
- It holds the cuttings upright (any potting medium except water should do this).
- It drains well and keeps the cuttings from getting too moist.
- Low fertility (no fertility really) means the energy of the plant goes into making roots and not foliage.
- It is sterile since there is no organic matter for diseases and microbes to lurk.
- The roots have an easy time penetrating the sand and put on some good initial growth.
- It's cheap! (Perhaps the best reason of all.)
- It's easily available at pretty much any hardware store.
Once the cuttings root they need to be transplanted into soil to gain the nutritional value of the soil. Plants that are easy to root (like forsythia, caryopteris, coleus, etc.) will do fine in soil but more difficult rooting specimens may simply rot in soil as opposed to vermiculite or sand as a medium. Peat can be used mixed together with either sand, perlit, or vermiculite and it maintains sterility due to its high acid content.
Why don't I use soil? Let's assume we are talking about garden soil and not soilless potting mixes you find in stores for seed starting. Those should be fine for any propagation purpose. Not all cuttings root easily in soil, but then again not all cuttings root easily. The difference in the sand vs. soil issue is the sterility of the soil. Here is what the Master Gardener Extension at Ohio State University had to say about the medium for cuttings:
"Insert treated cutting in a moist rooting medium. A suitable rooting medium is half perlite and half sphagnum peat moss. Any disinfested container with drainage is acceptable for use."
Here's what North Carolina State University had to say on the subject:
"The rooting medium should be sterile, low in fertility, and well-drained to provide sufficient aeration. It should also retain enough moisture so that watering does not have to be done too frequently. Materials commonly used are coarse sand, a mixture of one part peat and one part perlite (by volume), or one part peat and one part sand (by volume). Vermiculite by itself is not recommended, because it compacts and tends to hold too much moisture. Media should be watered while being used."
The problem with soil is that unpasteurized soil can contain bacteria. fungi (like damping off) and microbes that may harm a plant's growth or contain viruses that may spread to other plants. If it is too fertile it may encourage leaf growth (due to nitrogen) which you don't want at the initial stages of rooting, you want roots!
So in the end it comes down to personal preference. Many gardeners have methods of making potting mixes with different combinations of materials for different purposes and rooting plants is the same way. The sand works for me, but if a different rooting medium works for you then by all means use it. As long as the plant is healthy and happy in the end that's all that matters!
What soil mediums do you use for rooting, potting or seed starting? Do you have a favorite mix you use?