My ever-popular Flopping Jade post from last year prompted a question this past week that serves as the basis for this final 2018 hip, non-hipsta’ garden post.

I was asked, “I have a jade I was given. I have no southern facing windows to put it in. I want to put a plant grow light on it instead. How many hours per day should the light be on? It’s a full spectrum plant light.”

Jade is a succulent plant which is able to tolerate lower light conditions. When considering location for plants, I ask myself a couple of questions. First, what are the natural conditions under which the plant I have chosen will grow? This information tells a lot. Succulents, as a rule, are adapted to climates at the planet’s extremes with abundant, high light intensity and limited moisture from low latitude and altitude to high latitude and altitude. Thus, most growing guides suggest six to eight hours of outdoor sunlight (origins: South Africa) in dry conditions. The next question or thing to consider is the environment into which I am looking to stick my chosen plant. What are the environmental conditions of the space? How closely do onsite conditions match the conditions of plant origin? Lastly, I must decide one of two things based on how closely the two environments match. I could either select a new plant option (i.e. don’t fight the site; right plant, right place) or modify the onsite conditions to fit the plant’s needs.

Site modification in terms of lighting is what we are facing in this case. There are three aspects of light to consider with plant growing needs: quality, quantity and duration. Quality refers to the spectrum of light; quantity refers to light intensity (how many energy units per unit of time, i.e. photons). Duration, of course, is self-explanatory to my brilliant readership.

In this particular case, there is no great direct or indirect light source (south facing window), so the inquirer has rightly purchased supplemental lighting. There are a million great online resources regarding grow lights for succulents, so I shall not rehash it all. The inquirer’s full spectrum light contains both ends of the the visible light spectrum needed for plant growth (red and blue light). That takes care of quality. There are two aspects of light quantity to consider which affect duration. First, what is the distance the light bulb is from the leaf surface. Light intensity is inversely proportional to distance traveled. The further away the bulb, the more likely the jade plant will stretch and flop. I have found it is key to set up your light source so the distance from the plant can be adjusted as the plant grows. Also, a person should consider how much area the light covers at any given height. The second “quantity” consideration is the bulb’s wattage. Once you have determined these two aspects, you can answer the question of duration. In most cases, twelve hours of supplemental light meets the needs of six to eight hours of sunlight. This seems to be true whether growing succulents or starting most vegetable seeds. I use a simple plug-in timer available at any hardware store to handle this situation. Twelve hours is a good guideline, but a bit of experimentation might be necessary to find what works best in each specific situation.

Josh Steffen, Horticulture and Facilities Manager