Preparing to transplant/harden off plants to the outdoors in the Northeast
Quite possibly the most important part of your cannabis grow will be taking plants that have been sheltered under lights indoors and placing them outside to their final grow spot. If you were to head outside on the first sunny day of the year and tan for 6 hrs it would not go well. Your tender cannabis plants are no different. You must gradually expose the tender plants to the wind, sun, and rain; toughening them up by thickening the cuticle on the leaves so they lose less water when exposed to the elements. This will ensure a smooth transition and avoid setbacks of transplant shock and even death.
Ideally planting dates in Maine will be somewhere between May 15 and June 15. Soil temperature is the most accurate way to know when is right. A minimum soil temp of 60 degrees is recommended. Soil temp can be checked by using a probe thermometer. When growing in pots this can happen as early as Mid May, in the ground it will typically take until June 1 (this is normally when we plant in Auburn). For our growers further North in climate zone 4 it is advantageous to wait until Mid June.
At least one week before your anticipated planting date is when you should begin hardening off plants. I would recommend bringing them out on a mostly cloudy day on day 1 ensuring they don’t see more than 30 minutes of direct sun throughout the day. This can also be done by placing them out in a shaded or partially shaded area on a sunny day. Each day after, gradually increase the sun exposure by an hour a day. If the nights are still below 50 bring your plants into a sheltered, warm spot at night.
Now that your plants are hardened off they are ready to be transplanted. This should be done on a cloudy day either early in the morning or late in the afternoon. Prepare your soil in advance. If going into the ground the root zone is typically only 1ft deep but as wide as 6ft in all directions so place your compost and amendments accordingly. Dig your holes and water (ideally warm water) immediately after transplanting. We leave soil surrounding the plants clean and bare until around July, at which time we mulch heavily with bark, straw or cover crops. This will allow the soil to warm and discourage slug/snail outbreaks as they will have no place to shelter. Once the days have warmed and the threat of slugs has mostly passed it now becomes important to conserve soil moisture which is why we mulch. This will significantly cut down on water and nitrogen needs as nitrogen is water soluble and will gradually wash away with constant watering.