Greenhouse Propagation - How much mist should a misting system mist

... if a misting system could mist mist? -- I emailed this question to my friend and advisor Denise Polk, co-chair of our CNPS chapter's propagation group. Denise has worked in the horticultural production industry for many years. She kindly gave me permission to share her very helpful email as a guest post. (For info about putting in the misting system see the prior post, Installing an Automated Greenhouse Misting System.)

Denise writes:

I find that seeds only need a good long misting once a day at the most.

The soil just needs to be thoroughly moist and soil will often stay that way for several days depending on conditions, of course, in that sunnier warmer weather the soil will dry out faster. But in rainy weather and/or in shady conditions the soil can stay moist for days. Too much moisture could attract fungus gnats and damping off of the seedlings.

For seeds, you'll have to see if, over time, this misting regime is enough to wet the soil to the bottom of the container that the seeds are sown in.

Cuttings are another story.

They don't have any roots to draw up water to compensate for the evaporation from the leaves. Mist frequency & duration depends on types and condition of cuttings, the weather, location of the mist bed and the size of the water droplets/type of mist. 

In general mist only goes during the daylight hours and only as necessary to prevent wilting. The propagation medium should not be getting water logged. Good drainage/aeration is essential for healthy root development. Your current settings [i.e., a few seconds every 45 minutes] look like a good starting point for cuttings.

For the cuttings the mist system is primarily to keep the humidity around the foliage thus preventing the leaves from desiccating until the roots form, rather than to wet the cutting mix (tho the mix does need to stay moist too). Often times the cuttings are watered in by hand to moisten the mix and the mist system is used to maintain the humidity. It is really all trial and error as there are so many variables involved. And mist settings can get changed frequently with changes in weather/light and as the cutting material changes or starts rooting.

Thanks Denise! - I'm going to order another pressure regulator and filter and mist head parts so I can add a row of misters on the lower propagation bench -- then I can set up one for seeds and the other for cuttings.