1. Introduction
Considering the advancement of medical technology and declining birthrates, an aging population structure society has become a widespread phenomenon in developed countries around the world. The issues faced by an aged society are getting more attention from the government and the population. Taiwan became an aged society in March 2018 [
1]. Each individual’s cause and degree of aging is different, and aging includes functional aging, psychological aging, pathological aging, and social aging. According to a report in 2015, by the Ministry of Health and Welfare of Taiwan, the healthy or subhealthy accounted for 83.5% of the elderly population in Taiwan and the disabled account for 16.5% [
2]. Whether healthy or disabled, as the elderly population ages they must face the decline of physiological function and cognitive function, which leads to the negative impact of their physiological, psychological, and social functions [
3,
4,
5,
6]. Studies have indicated that elders who contact nature or plants or engage in horticultural activities could maintain health, delay aging, and improve the benefits of physical, psychological, cognitive, and social functions [
3,
5,
7,
8,
9,
10,
11,
12,
13,
14,
15,
16]. Horticultural activities can also be used as a method for rehabilitation or an adjuvant treatment of chronic diseases. In addition, horticultural activities are popular and common leisure activities for the elderly [
3,
9,
17,
18,
19,
20,
21]. One study revealed that investing in the development of disease prevention can save significant costs, as each person spends
$10 per year and the rate of return is 5.6 times after five years [
22]. The national health expenditure spending for chronic disease and long-term nursing institutions increased 1.23 times between 2015 and 2018 in Taiwan [
23]. It is perceivable that prevention is better than a cure. Perhaps delaying aging through healthy horticultural activities can improve health as well as help avoid the cost of medical and long-term care [
12,
24].
There are many types of horticultural activities, including static and dynamic, indoor and outdoor, and touching plants. Horticultural activities are often used as auxiliary treatment methods particularly [
9,
21,
25,
26] because they stimulate the five senses [
18]. The current general horticultural therapeutic activity types are summarized as follows: cultivation technique, artistic creation, food tasting or smelling, flower viewing, guided tour, making daily necessities, and so on [
4,
7,
12,
15,
17,
21,
26,
27,
28]. Each type of activity has different benefits and should be used as an improvement policy for different objects with suitable activities. In addition to the types of activities, the activity field is also extremely important. Studies revealed that the indoor environmental factors, such as air quality and temperature, affect learning and health [
29,
30,
31,
32]. Therefore, the quality of the environment must also be considered during the event.
Many studies have confirmed that heart rate variability (HRV), blood pressure, pulse rate, and cortisol values can be measured before and after an activity to understand the benefits of the activity on the participants [
28,
33,
34,
35]. Psychological stress affects the body in two main ways: the hypothalamus-pituitary-adrenal gland axis and the sympathetic nervous system [
36]. When people feel stress, the sympathetic nervous system becomes more active, which is related to increased heart rate. When this stress disappears, the parasympathetic nervous system decreases the heart rate [
37]. The response of the autonomic nervous system can be monitored by the HRV. Therefore, HRV may be used as an objective assessment of stress and mental health [
36]. HRV parameters include high frequency (HF), low frequency (LF), and the standard deviation of the normal-to-normal (NN) intervals (SDNN). The HF power is mainly mediated by parasympathetic nerves; the LF power is mainly mediated by sympathetic nerves [
36,
37]. The LF value decreases and the HF value increases when relaxed. It can also be evaluated by the ratio of the LF over the HF (LF/HF) [
38]. SDNN is a measure of the total power in the analyzed segment [
35,
39]. When the SDNN value increases, it is an index of physiological resilience against stress [
36]. The pulse and blood pressure tend to slow down as the mood relaxes. In addition, cortisol levels can represent the mental and physical states [
4,
40], however, the analysis time is longer and not instantaneous. One study confirmed that salivary amylase activity (SAA) is positively related to it and is used to express the current stress index. When the mood is nervous or more stressed, the SAA value is increased [
40,
41]. Moreover, we can use questionnaires or scales to understand more subjective mental states [
16,
42]. Commonly used questionnaires are the Profile of Mood States (POMS) [
33,
34,
43], Life Satisfaction Index [
5,
16,
44], stress scale [
28], and depression related scale [
6,
15,
18,
24]. Many studies have explored how contact with nature and engagement in horticultural activities affects mental states [
5,
6,
7,
16,
33,
34,
42]. Results have shown the positive emotions increased and the negative emotions decreased for five types of people. First, the elders living in nursing homes who were cognitively intact, and no visual or auditory impairment occurred to them [
5,
7,
16]. Second, the elders with depressive symptoms and memory problems [
6]. Third, middle-aged and elderly individuals with or without chronic diseases [
34]. Fourth, those with cardiovascular disease [
42]. Finally, the elders [
44] and adults [
33] without diseases.
Finally, whether it is horticultural therapy for people with diseases or horticultural activities for healthy or subhealthy people, many studies have confirmed that these activities can effectively improve physical and mental health, increase well-being, and achieve the effect of delaying aging [
7,
8,
17,
18,
26,
42]. However, few studies have explored the impact of activity types on the elderly. Therefore, this study selected three types of horticultural activities (culture technique, artistic creation, and food tasting) to measure blood pressure, pulse rate, SAA, and questionnaire responses before and after each activity. HRV was monitored throughout the process to understand the status of the elderly during activities. The results of this study can be used to plan healthy horticultural activities for the elderly in the future to delay aging, increase healthy and active aging, and increase happy learning.
4. Discussion
This study compared the physiological and psychological responses to the types of horticultural activities among elderly individuals. Pulse rate and SAA were determined to be lower after every activity. Previous studies indicated that when the mood is relaxed, the pulse rate is decreased [
34,
42]. SAA represented the current state of mental stress and physical fatigue because these measurement values decrease when a person is relaxed [
40,
48,
50]. Considering this, the four horticultural activities in this study had a relaxing effect on the elderly. Moreover, previous studies showed that blood pressure is significantly lower in the horticultural therapy program [
27,
51]. However, systolic and diastolic blood pressure were not significantly lower after every activity in this study. It might be that previous studies were mostly long-term programs which could explain the tendency for the blood pressure to decrease [
16,
27,
51]. This study mainly focused on relatively short-term activities, so there was no significant decrease in blood pressure. The results of
Table 6 showed that the effects of five activities on the changes of physiological indices, the four horticultural activities’ SAA, pulse rate, and LF/HF decreased significantly. It showed that it was relaxable and pressure relievable. Previous studies indicated that SAA, pulse rate, and LF/HF can represent immediate emotion and pressure [
38,
40]. This is the reason why SAA, pulse rate, and LF/HF are used for the level of pressure relieving of short-term horticultural activities, which is consistent with the findings of previous studies [
33,
34,
50]. Considering the changes in SAA, pulse rate, and LF/HF in this study, we found that Rocky Leaf Prints (artistic creation) and Herb Tasting and Smelling (food tasting) were better to relieve the stress and anxiety of the elderly.
HRV measurements have also been used to evaluate emotional and health-related physiological effects [
33,
37,
39,
52]. The ratio of LF/HF can be used to represent the change of sympathetic and parasympathetic nerves. When the ratio of LF/HF decreases, it indicates physiological relaxation [
33,
52]. Higher SDNN reflect a lower mental effort [
53]. In our study, LF/HF decreased and SDNN increased after participating in the four horticultural activities. The ECG was worn throughout this study, so we interpreted the changes in LF/HF and SDNN in the four phases (pretest, activity content explanation, healthy horticultural activity, and post-test) of the activity. During the process of these four horticultural activities, there was a downward trend in phase 2. This means that it was more relaxable. Perhaps the reason is related to the instructors’ teaching styles. Some studies indicated that students’ learning outcomes [
54] and learning anxiety [
55] were related the instructors’ teaching styles. To avoid the error of experiment caused by instructors, the same instructor was used in these four activities. The instructor explains the activities in such a way that testers pay attention and listen carefully. This made them calm down, which caused relaxable effects. In phase 3, due to the activities, there was an upward trend of LF/HF and SDNN. After joining four different types of horticultural activities, compared to the pretest, the downward range of LF/HF was caused by different effects of four activities. Observing the emotional and physiological changes of the elderly during the horticultural activities can be used as a plan for future activities for the elderly.
Previous studies showed that horticultural activities had mental benefits for the elderly [
13,
16,
33,
42], which is consistent with our findings. The POMS questionnaire indicated that the negative mood states were significantly lower after the four horticultural activities. Additionally, the positive mood state of vigor was significantly higher, and the total mood disturbance decreased significantly after the horticultural activities, except for Grass Doll. Therefore, we concluded that the types and materials of horticultural activities (with plants or without plants) affect the mental state of the elderly.
Regarding the changes in pulse rate, SAA, LF/HF, and POMS in this study, we found that artistic creation-type (Rocky Leaf Prints) and food tasting-type (Herb Tasting and Smelling) showed better effects in these activities. Maybe this is because they are able to create freely and experience immediately making their effects better. In addition, culture technique-type was better than the control group. However, the effects were less than types of artistic creation and food tasting. This is due to the long-term effects of the culture technique-type, such as taking care of plants and observing seed germination and the growth of plants. Previous studies were mostly in the plan of long-term horticultural activities [
16,
18,
24,
27], so there was a benefit in their studies about culture technique-type.
In the culture technique-type, Kokedama had a more relaxing effect than the Grass Doll. According to previous studies, contact with plants is more relaxing than contact without plants [
33,
49,
56,
57], which is the same as this study. Kokedama involved contact with plants during the operation, which may be the reason the effect was immediate. The Grass Doll was a sowing activity; therefore, its main benefit was in the follow-up observation of seed germination and continued activities. We concluded that for short-term horticultural activities, we can arrange the artistic creation and food tasting types to have as much contact with plants as possible.
Many studies proved that horticultural activities increase happiness and also improve physical and psychological status [
8,
18,
25,
26]. However, fewer studies discussed the benefits of different types of horticultural activities. Therefore, this study researched the effects of different types of horticultural activities. Hopefully, it can be used as the planning of the horticultural activities in the future. Horticultural activities are not only convenient in operating but also in material gathering. Besides, compared to forest healing [
34], area limits do not exist. Activities can be conducted in senior citizens learning camp and long-term care facilities in cities. Nevertheless, there were still some limits. Firstly, the same instructor was used in these four horticultural activities. Besides, it is required for the instructors to be trained so that they are skillful, since the teaching style affects the effect. Second, the POMS scale had many questions and took a long time to answer since the object of this study was elders. Hopefully, a simplified and reliable scale can be obtained to evaluate the effects of activities for elders. Third, in evaluating physical and psychological status, we did not observe significant changes in the blood pressure and SDNN. Previous studies are mainly about the discussion about the effects of joining long-term horticultural activities [
16,
24,
27]. Therefore, blood pressure can be used as the assessment of long-term horticultural activities; however, it was unable to indicate the results immediately. Besides, this study can evaluate the items of effects on short-term activities. SAA, LF/HF, pulse rate, and POMS are included. Hopefully, we can understand how different types of horticultural activities benefit each age range by using this method and promote learning effects through different types of planning about horticultural activities. This can be used for activity planning in the future, achieving the benefits of healing and pressure relieving while also promoting social well-being.