HOW DO PLANTS DRINK WATER?

Water is absorbed by all plant parts. In healthy plant it works as a pumping station: from roots - through stems - to leaves and flowers/fruits.
Water also absorbed through leaves: from humid air an/or dew.
There are some rainforest species that naturally prefer high air humidity, and you can't blame them for this like you can't blame seaweed for living in water.
For most of non-aquatic and non-rainforest plants, when the plant and especially root system is healthy and developed, the "pumping station" works just fine and a plant doesn't require extra air humidity within their natural habitat preferences range (humid tropical climate or dry desert, etc).

HOW DOES AIR HUMIDITY EFFECT PLANTS?

Two sides of the coin. High air humidity means:
- GOOD: a plant and especially foliage grows much faster. By providing humid environment, you provide easy access of water to all plant parts while there is still a good air circulation (humid air is different than soaking in water where the plant may start rotting in a few hours without air access unless it's aquatic). Plant doesn't have to control evaporation in order to save water, so it can grow very large leaves.
- BAD: by getting used to easy water access, the plant root system becomes weaker and smaller - the plant simply doesn't need as much roots any more, water supply comes mostly from absorbing by leaves. This is why you may see many rainforest species with tiny root systems (bromeliads), while desert plants like Agave have huge roots going down for many feet and exceed the plant size many times. Same thing happens to greenhouse plants that were kept in artificial micro-climate: they sometimes have small root system and in order to survive outdoors, need some adjustment period for developing root systems.

Mist house, especially fog-house, has nothing to do with more frequent watering. The idea of the fine mist is to create a humid air creating fine water sprays during short periods of time. Most of the water, ideally, stays as a dredge in the air and doesn't soak the soil. Sometimes mist-houses are equipped with a separate irrigation system - for watering the plants, because if the mist/fog system is made right, it shouldn't provide enough watering for a root system if any.

There are several reasons why you may use a mist-house.
1. For plant propagation: cuttings (no roots to start with, then small roots)
2. For recovering bare-rooted plants after shipping stress
3. For helping sick plants to recover
In each case, the main purpose of creating a high humidity is to supply the plant with necessary water amount while it can't obtain it naturally through root system whether it is damaged or simply doesn't exist.

1. Plant propagation.
The proper procedure to make cuttings differs for different plants and we won't dicuss it here. You can find more information in books or on the Internet.
Depending on species, the cuttings are kept under mist for a few weeks in a loose soil-less mix with lots of perlite (perfect mix is half coconut fiber and half perlite with a bit of Osmocote as a starter) until well-rooted (root ball fills the cell). Normal mist mode is: "5 sec on - 2-5 min off".
The main idea is to keep leaves wet (not soil!). If you overdo misting time, the soil will get wet and cuttings may rot. If you underwater - leaves will get dry, the cutting gets wilted and will die eventually. You have to experiment to determine the right timing. When preparing the cuttings, cut of excess leaves to limit eveporation, but at the same time make sure to have enough of leaf surface for water absorbing. If you leave bare twigs, most likely they won't make it because the stem surface is not enough. The optimal will be 3-4 leaves, and if they are too large - you may trim them to a half-size or so.
Transplant your rooted cuttings only when they have enough roots developed. Usually, when the cutting starts growing new leaves and shoots, the size of the new growth is somewhat proportional to the size of roots.

2. Establishing bare-rooted plants.
After the plant was bare-rooted (all soil was washed off), the root system pumping ability is practically lost. Micro-roots (hairs) that actually do the "suction" job, are destroyed. You won't see those hairs unless you have a microscope. Visually root system stays intact, but the thick roots are only "vessels" that carry water to the rest of the plant, while the little hairs do the absorbing part. So the root system becomes almost useless. It is no more helpful than other parts of the plant, like stem for example. It absorbs as much water as any non-root part, while the root tissue is very susceptible to rot. Slightly overwatered - and the root gets wet, rotted, brown and dead. If you ever saw overwatered orchid roots, sitting in a wet sphagnum moss without air circulation - you know what happens.

For establishing bare-rooted plants it is important to provide the following:

• small container - the smaller the better. Don't be afraid to stick a 3 ft tall plant into tiny 4" pot, even to trim roots if needed (they have to re-grow the little "hairs" back anyway, and too huge useless root system will create extra chance for rotting)
• loose porous medium: perlite (a lot), some coconut fiber or soil conditioner (bark). Remember you have to avoid rotting by providing good drainage and good air circulation within the container - only in this case the new "hairs", young roots will grow back.
• fine mist or fog to keep leaves wet at all times to provide plant with enough water through leaves absorption.

Rate of misting depends on plants. Some requires more, some less. Some plants can evene recover in one-two days. Normal mist mode should be like for cuttings to start with, then in 2-3 days decrease frequency of sprays, gradually going down to "5 sec on - 30 min off " schedule in 1-2 weeks. By the end of treatment, you don't have to keep leaves wet at all times unless you see a need.

It's very important not to overwater root system. Make sure plants don't sit in water and have very good drainage. In our experience some plants are encouraged by short period (few hours) of "droughts".

Filtered bright light is the best. On one hand, you don't burn the tender leaves and keep eveporation under control, on the other hand you still provide enough light for vegetative process. Besides, brighter light kills fungus.

Your misthouse should be covered with planting all the way around. This will keep humid air in and protects sensitive plantings from undesired rain, since you need to control amount of water coming into pots. However, the tricky part is - a) you have to provide good air circulation (you don't want fungus and mold be your guests) and b) with high afternoon temperatures, the plants may get "cooked" under plastic where temperature may reach 90F and higher (critical number). Providing windows and in-window fans at the ceiling level is a good solution.

To limit amount of sun, you may use a shade cloth over the plastic (as many layers as needed) - this will also desrease temperature inside. Plastic reflecting film or paint can be also helpful.

When you plant cuttings or bare-rooted plants in a well-drained medium that is not susceptible to rot, most likely this medium doesn't have much organic in it, which means nutrients. Once your plant started to root or recover, it will continue growing, and will need not only water, but food as well. This is why we add a bit of slow-release fertilizer in propagation mix - so once the plant has a tiny root, the meal is ready for it. However, even with fine fog the soil gets flushed very soon, and no nutrients left. After the first new roots or shoots appeared, apply some fertilizer. You may add more slow-release granules like Osmocote or Dynamite, or spray with 1/2-1/4 doze of water-soluble fertilizer over the foliage once a week, at evening hours.

Using Micro-elements supplement is even more important for young and establishing plants. Iron-deficiency is a very common problem with cuttings and stressed plants.