Bach flower therapy
Bach flower therapy is an unproven health treatment which asserts that flowers contain the life force of a plant, and that this life force can be imprinted into water through "sun infusion". The resulting plant extract is diluted to create remedies, which are usually ingested by the patient, and are purported to help them let go of "negative thoughts". The practice was originated and developed by English homeopath Edward Bach (pronounced "Batch", 1886–1936). The 38 specific plant remedies that he devised, and the emotional states for which they are indicated, are listed on the Catalogs subpage.
There is no rational or scientific basis for believing that Bach flower therapy would have any effects beyond those that are induced by suggestion - i.e. placebo effects, and it is not something that has been considered worthy of any serious scientific attention. There have been a few assessments of its effects on patients, and it is thought to probably be safe. Like other healing rituals that work through the power of suggestion, it may have some benefits in relieving anxiety, with some consequential health benefits. 
For healing rituals generally, their effectiveness in evoking benefits from the placebo effect depends on getting patients to believe in the possibility of their efficacy. Different healing rituals appeal to different patient groups according to how open they are to mystical, religious, or quasi scientific explanations, but in all cases the suggestive power is bolstered by an elaborate explanatory narrative the purpose of which is to convey a sense of apparent profundity to the ritual. In the case of Bach flower therapy, there is some evidence that spirituality as a personality trait might heighten responsiveness to this therapy 
While Bach remedies are derived from plants, the principle is different than herbalism. Whereas herbalism assumes the existence of significant healing ingredient(s) in the plant extract, and thus presents a quasi-scientific narrative explanation, Bach remedies are given a mystical, or supernatural narrative. Bach uses the term "signature", said to be related to the "signatures" of Paracelsus, invoking the authority of an ancient wisdom. The remedies are said to work on a mental level that transfers the "vibrations" or signature; the vibrations resonate with inherent vibrations believed to be in human cells. According to Bach practitioners, the remedies do not have detectable levels of active chemicals. Independent microchemical analysis does not appear to be available.
Aromatherapy is a similar unscientific healing ritual, and also makes use of flowers as a source of aromatic oils, but the preparation methods are different. Bach extracts use, in chemical terms, solvent extraction, while essential oils are usually extracted with steam distillation.
Preparation of Bach remedies
Bach flower therapy and homeopathy claim to improve a vital force, and they both have a concept of potentizing. At that point, however, they diverge. Preparation of the remedies is different, and Bach remedies are not selected using the homeopathic principle of the Laws of Similars. A Bach remedy is chosen to treat a particular psychological causes of illness. For example, the flower 'impatiens' is used to treat impatience and irritability, and 'mimulus' is used to treat timidity.
Bach remedies are prepared using precise methods specified by Bach, and which are also described in the British Homeopathic Pharmacopeia as used to prepare homeopathic mother tinctures. This is an atypical use of the term "tincture" in the terminology of herbalism and pharmacy, which use the term for an alcoholic, not aqueous, extract. Only flowers that grow naturally in the wild are used, and remedies are prepared using either the "sun method" or the "boiling method". In the sun method, fresh, fully opened flower heads are floated on pure spring water in a glass bowl and left for a few hours in the sun; in the boiling method, branches and leaves are boiled in water for half an hour. The plant matter is then removed, leaving the water (the "mother tincture") which, according to Bach, retains the "vibrations" of the flower. The mother tincture is then mixed with brandy, and either diluted with water for a remedy to be taken orally, or applied directly to pulse points such as the wrists, temples and behind the ears.
Once extracted, the tincture is used in a very different manner than in homeopathy. There is dilution, but to what homeopaths call a 5X dilution, which gives a much higher concentration than used in homeopathy. 
- Select Committee appointed to consider Science and Technology, U.K. Parliament (21 November 2000), Chapter 2: Disciplines examined, Definitions of the Various CAM Therapies, Complementary and Alternative Medicine
- Our founder, Dr Edward Bach, Bach Centre
- Ernst E (2010) Bach flower remedies: a systematic review of randomised clinical trials Swiss Med Wkly 140:w13079. doi: 10.4414/smw.2010.13079 PMID 20734279
- Thaler K et al. (2009), "Bach Flower Remedies for psychological problems and pain: a systematic review", BMC Complementary and Alternative Medicine 9: 16, DOI:10.1186/1472-6882-9-16
- Halberstein R et al. (January 2007), "(Abstract) Healing With Bach® Flower Essences: Testing a Complementary Therapy", Complementary Health Practice Review 12: 3-14, DOI:10.1177/1533210107300705}
- Whalley B, Hyland ME (2009) One size does not fit all: motivational predictors of contextual benefits of therapy Psychol Psychother 82:291-303 PMID 19288979
- Hyland ME et al. (2006) Spirituality predicts outcome independently of expectancy following flower essence self-treatment J Psychosom Res 60:53-8 PMID 16380310
- The Principles of Bach Essence
- The Production of Bach Flower Essences
- The Theory of Bach Flower Therapy
- Halberstein RA et al. (2010) When less is better: a comparison of Bach Flower Remedies and homeopathy Ann Epidemiol 20:298-307 PMID 20097577