Tomato and sweet pepper vegetables contain large proportions of vitamins A and C whose deficiency leads to night blindness and scurvy disorders, respectively. Moreover, they are sources of income for many households in Tanzania through provision of formal and informal employment to growers, traders, researchers and other allied workers. In recent years, organic production has gained popularity due to environmental and health concerns over pesticide and fertilizer residues in food. However, organic production of high value crops like tomato and sweet pepper faces many challenges because methods used must be organically feasible.

Mulching is one of the organically accepted techniques that is highly emphasized in organic production systems for its role of suppressing weeds, conserving soil moisture, providing nutrients upon decomposition, conserving natural enemies of insect pests by providing them with a suitable habitat, moisture, protection and alternative prey.

Farmers commonly use star grass, banana leaves, bean plants and pods and other crop residues as mulch. However, several challenges have been associated with the use of these common organic types of mulch such as an increase in labour cost in terms of time and money as most of these mulches require frequent replenishment, scarcity as most of them are also used as animal feed and seasonal availability which does not guarantee a year-through supply of mulch. Challenges associated with such commonly used mulches in Lushoto district has diverged attention towards alternative organic mulches.

Mexican weeping pine (Pinus patula Schelde. ex Schltdl and Cham) and wild lemon grass (Cymbopogon spp.) were used as mulch in organic production of tomato (Solanum lycopersicum L.) and sweet pepper (Capsicum annuum L.) to evaluate the effect of type of mulch, time of applying mulch and influence of seasons on yield. The study was conducted at Lushoto and Ubiri wards in Lushoto district, north-eastern Tanzania.

Results showed that both types of mulch had positive influence on yield and other production and quality components regardless of the time of mulch application. Results also revealed that among the three seasons of growing tomato and sweet pepper over a complete year cycle, the highest yields were obtained during the wet and cold season (April - August). Pine and wild lemon grass also lasted throughout production time without the need for replenishment.

Pine and wild lemon grass matrials used in this study performed well in supporting growth and yield while protecting quality of tomato and sweet pepper, controlling weeds and providing habitat for beneficial arthropods. This discovery is important not only  in organic farming but in other production systems as well.