1. Introduction

Since the advent of the 21st century, phenomenal changes in human civilization have been witnessed throughout the globe. People are opting to live in big cities, where they enjoy diverse amenities. The land around cities is being used for commercial purposes and converted into malls, housing developments, roads, and small and large industrial establishments. This trend of population concentration in urban areas has created problems, such as a reduction of farmable land, increased malnutrition, and increased distances to traditional sites for food production ^[1]. In addition to these urban problems, the general increase in population, food scarcity, and climate change are emerging concerns of this century, globally ^[2].

The world population is increasing exponentially, and according to some estimates, it could grow to 9.6 billion by 2050 ^[3]. In the future, there will be pressure to increase agricultural productivity to fulfill peoples’ need for food, while, at the same time, water and land resources are being rapidly depleted. The earth's climate is always changing, and there have been persistent increases in temperature. Under these circumstances, 10% of agriculture land may become uncultivable for farming ^[4]. The variability in weather due to climate change is threatening food production and distribution systems, and a significant number of people throughout the world are suffering from hunger and malnutrition ^[2][5]. This scenario varies within (and between) developing and developed countries of the globe. In addition, several anthropogenic activities, such as applications of unbalanced fertilizers, pesticides, inappropriate farming practices, and usage of heavy machinery, have resulted in soil degradation and depletion of fertile land ^[6]. Besides poverty, the documented migration towards urban areas, lack of resources, natural disasters, and conflict are key constraints of food security. Moreover, the reduced availability of fertile land, crop production, and high market prices of agricultural products have also limited the food supply ^[7].

Recently, the outbreak of novel coronavirus 2019 (COVID-19) has reached pandemic proportions and has disrupted the food chain in different ways. It has constrained peoples’ capability to access food by reducing income and increasing job insecurity. Further, worldwide lockdown strategies have increased transportation interruptions, labor shortages, and limited market access, which has resulted in food loss and waste ^[8]. Countries with the highest food insecurity levels were less prepared for the COVID-19 outbreak. Globally, governments have implemented lockdown policies to secure their citizens during the epidemic. However, there has been uncertainty in developing countries, regarding feeding their people under these conditions. Moreover, with this pandemic, the major threat for developing countries is hunger, as more people will die due to hunger, instead of the disease, if lockdowns continue to persist. In effective lockdowns, approximately 40% of a population would be unable to stock food for 14 days, and in just three days, most families would start to suffer from hunger ^[9]. The current COVID-19 pandemic has emphasized the importance of local food production ^[10].

Under the above circumstances, ‘‘Urban Horticulture’’ has emerged as a viable concept with the aim to provide sufficient fresh and safe food to cities, to achieve a sustainable food supply and food security. “Urban Horticulture” is the cultivation of fruits, vegetables, mushrooms, herbs, and aromatic and ornamental plants that can grow easily in a city and its surroundings ^[11]. The current COVID-19 pandemic, and lockdowns, have resulted in advantages to city dwellers who grow fruit and vegetables at homes, providing an opportunity to enhance urban horticulture. People, planners, and governments all are rethinking ways to utilize vacant lands in cities for food production under this dynamic condition ^[12]. Kitchen gardening is an older term, with a similar concept, in which edible plants are grown in home yards/gardens and rooftops to satisfy some of the home requirements for food. Many horticultural crops are considered ideal in urban agriculture production systems because they occupy a small space, produce more per unit area, have high nutritional value, and short production cycles. For example, diverse vegetable crop species may be grown and harvested within a short period of time (60–90 days) or even less for some herb/leafy crops ^[13].

In low income urban areas, the dietary deficiency of micronutrients, such as iron, zinc, iodine, and vitamin A is more common ^[14]. Horticultural commodities, such as fruits and vegetables, are rich in minerals, fibers, and bioactive compounds (e.g., phenolics and antioxidants), and have the potential to reduce malnutrition. Moreover, when these products are fresh and hygienic, this local food supply can have multiple positive impacts on humans, such as strengthening social cohesion and the local economy ^[15][16]. It also increases positive attitudes toward nature and natural habitats ^[17].

In recent years, interest in urban agriculture has increased because of climate change and the desire for a sustainable food supply in urban localities ^[18][19]. Urban horticulture has furthered its significance during pandemic diseases, such as COVID-19, which, globally, has triggered food insecurity. Moreover, higher poverty rates, malnutrition, stunted growth, and rising populations across the world have enhanced the importance of urban horticulture ^[13]. To fulfill the food needs of people, vacant spaces in urban areas will be a prime priority in order to compensate for lack of food and urban ecological losses if land is left barren. Growing horticultural food crops in urban landscapes, and open spaces, will improve the sustainability of food and the environment. Urban horticulture is, essentially, a way to mitigate societal social challenges (Figure 1).