When starting seedlings or clones, it’s important to provide special care and attention to allow your new crop to adjust to a new environment. Plant roots are very delicate and take time to adjust to new mediums. If roots are not cared for properly, they will deteriorate and the plant will no longer be able to uptake food and water. 

Some growers start their crops indoors where it’s warm and easier to monitor threats like pests and pathogens. Before the seedlings can be transitioned to the outdoors, it’s important to ensure that your plants have hardened so they are protected from becoming stunted, going into shock or even dying. This process requires patience and following the right steps. 

What is hardening? 

Hardening your plants consists of two main components

  1. Exposing and adjusting your plant to a new environment
  2. Acclimating your plants to direct sunlight and dark cycles 

The best way to harden your plants is to protect the roots while you gradually expose them to the sun’s radiation. There are many natural elements to be mindful of when hardening off your plants in preparation for the outdoors: 

  • Ground vs container transplantation 
  • Intense sunlight
  • High winds
  • Heavy rain
  • Humidity 
  • Pests and pathogens 

Timing is key when you begin the hardening process. Putting your plants outside too early or too late can stunt their development, or even kill them if the temperature is too cold. 

In America’s southwest, maximum available sunlight is around 14.5 hours a day. In places like Alaska, you can have 20 hours of sunlight a day. Take your location into account when planning to expose your seedlings to full sunlight. 

Finally, when planning your hardening process, make sure that no animals or insects have easy access to your plants. 

What happens to the plant as it hardens? 

Hardening off your cannabis seedlings before transplanting them outdoors, will reap huge rewards and set up your plant for a healthy and bountiful harvest. Some of the benefits include: 

  • Increased stem strength
  • Better root development
  • Reduced risk of transplant shock 
  • Reduced risk of sun burning
  • Improved airflow
  • Better nutrient uptake
  • Overall hardier and more robust plants 

The goal of hardening plants is to prepare them for outdoors. This enables them to survive cold nights, gusts of wind, and droughts. Most plants will harden up within a few days to two weeks, depending on environment.  

What are the risks of not hardening? 

Choosing to forgo a proper hardening off process can be risky. The sun’s intensity is far greater than any indoor grow light can provide. Putting your plants outside without a sun exposure schedule may result in leaves that turn downward, drooping, or crispy leaves. If the plant isn’t ready for full sun, they will suffer and growth will be stunted. 

Growing indoors creates plants that grow fast but with long, thin cells. Their stems and leaves will be more fragile. This is because the seedlings don’t fully develop the waxy cuticles that protect leaf surfaces from drying out. Hardening will strengthen the plant with sturdier stalks and prepare them for exposure to wind.

In dry, low humidity climates like Southern California, there are some serious risks if you don’t harden off your cannabis seedlings before transplanting outdoors. The heat and low humidity will suck all of the moisture out of the plants when the temperature spikes. This is because the roots can’t deliver water fast enough to the leaves. In hot and humid climates, plants have the opposite problem and the root zone can become waterlogged, reducing their functional effectiveness. The outdoors can be harsh on new plants so hardening off to prepare for sunlight intensity, dryness or humidity, wind and pests are critical to your plants’ survival. 

What techniques can I use to harden off my plants? 

There are several ways to prepare your plants for outdoor transplanting. You can combine these techniques in a way that fits your environment. Wait for a cloudy day to transplant your seedlings to ensure that after watering, the soil doesn’t lose moisture too quickly.

Provide shade

To protect young plants that arent acclimated to sunlight yet, place them under the shade of trees, or alternatively, a shade house. A shade house is a miniature greenhouse enclosure with material that filters sunlight. After a few days spent outside in the shade, you can move them into full direct sunlight for short periods of time, avoiding peak intensity mid-day between 11 am to 2 pm. Get your cannabis used to the strength of the rays and soon, your seedlings should be able to handle direct sunlight all day. 

Pots vs in the ground

Planting directly into the ground is the best way to protect the roots from being directly exposed to sunlight. If you are going to plant in pots above ground, keep your eye on your roots. If potting is your only option, consider some plant armoring products that add in vitamin B complex and potassium silicate. You want to build sturdy cell walls. When watering during high temperatures, use cool water to keep your cannabis seedling happy. 

Use a Cold Frame

A cold frame is another way to harden up young plants through a gradual process. Cold frames can be wooden boxes with glass tops or even just a piece of glass over soil. They help you protect smaller plants only using the heat from the earth and the sun, with no artificial heat. Put the setup in a south facing spot (if you are in the Northern Hemisphere), and the design will keep temperature low and provide protection from other threats like wind and animals. Keep the box closed for three days outside so seedlings can adjust, then open up the glass lid to start exposing them to sunlight. 

Use a Small fan

This easy and practical method involves using a small fan indoors to circulate air around the seedlings to toughen the stems against wind. Don’t point the fan directly at your plants. Instead, make sure the fan, on a low setting, is circulating air around the room in order to avoid drying out or damaging plants. 


Strong, healthy cannabis plants with potent and quality buds will require you to monitor your crops closely. When hardening off your plants, consider your unique outdoor environment including sunlight intensity, sources of shade, wind, and watering needs. 

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