10 Tips for Auto-Flowering Pot Plants

1) Plant within the correct time window.

In the northern hemisphere, the summer solstice arrives around June 21 with 16 to 22 hours of light (18 hours in the northwest of France, for example). That’s the point of maximum hours of sunlight per day, and at a better angle (i.e., more vertical) for full plant exposure.

In many areas, spring provides the right temperature to plant autos outdoors (a minimum of 58°F) at the end of May or beginning of June. If you plant (or transplant) them too early outdoors, they tend to produce small, premature harvests, especially since flowering will be accelerated by nights that are too cold. Below 45°F, you’ll encounter exaggerated stretching and stunted bud development.

Given the usual flowering time for autos (most begin to flower at two to three weeks), it’s wise to start them from mid-May to around June 10. This way, your plants get as much sunlight as possible each day, and their “flip” to flowering will occur as the length of days starts to diminish—a strong encouragement for them to start flowering vigorously.

2) Give your plants a healthy start.

Begin with proper seed storage: The best place is a clean fridge at 41°F to 46°F, with low humidity. All breeders store their seeds under these conditions, so don’t reduce your own seeds’ potential by using bad storage techniques!

You’ll need to be especially careful during germination. Soak your seeds in a glass of purified water with a pH between 5.5 and 6.0, and stick around to notice how fast they fall to the bottom of the glass. Some will even sprout in less than five hours! A glass of tap water will do fine unless you live in Spain or areas with highly polluted water. Always leave tap water out for 24 hours to allow the chlorine to evaporate.

Poke the seeds with your finger to push them under the water’s surface, and don’t let them soak longer than 12 to 24 hours. When you notice the first white germ sprouting, you can do one of two things. The easiest is to plant the seed directly into its final pot, which should be filled with a good soil mix available at your local grow shop. My preferences are Plagron Royalty-mix and Pro-mix, but any high-quality product, including Canna and Biobizz, will do. Also, place a half-inch layer of clay pellets at the bottom of the pot to aid in drainage.

Your second option is to put the popped seeds between two unbleached paper towels between two plates and keep them moderately moist. No water should drip from the paper towels; nor should they ever dry out. After a day or two, when you see that the seeds have cracked open and have a tiny root peeking out, carefully transfer them into Jiffy pots for the first 10 days of growth.

3) Provide your plants with the proper environmental conditions.

It’s important to always dial in the humidity level. Keep it near 80% during the seedling stage, then switch to between 55% and 70% toward the end of the vegetative stage (15 to 25 days from sprouting). In the absence of expensive humidifying equipment, place a dome (such as you’d use for cuttings) over each plant. This is a cheap, easy and very effective method during the early stages of growth. A clear plastic bottle works perfectly for the first week or so, and you can use it indoors, outdoors or in a greenhouse. A simple ceramic ultrasonic system can solve humidity issues in a small to medium-sized area under six by six feet. In a greenhouse, you can set a pipe with nozzles to mist water in the growing area and get a 5°F to 10°F cooling of temperature. The misting system should be coupled with a controller that manages ventilation, temperature and humidity.

4) Use the best growing medium possible.

No reason to cut corners here! Your harvest is directly linked to the quality of your genetics, grow medium, nutrients and environmental conditions. Remember, overwatering and overfeeding are the most common mistakes that a beginner can make.

Your medium needs to have the airiest structure possible, so anything you can add to improve aeration and water retention is a good thing: coco coir, clay pellets, perlite, vermiculite, etc. Here in Europe, we use Plagron, Canna and Biobizz, but in North America people seem to prefer Pro-Mix, FoxFarm and Sunshine Mix. Whichever option you choose, be sure it’s light, airy and has a pH range of 6.0 to 6.5. Your auto-flowering roots will grow as though they’re in a hydroponic system.

5) Don’t over-water!

One of the worse things that can happen to a plant is too much water: The roots become suffocated and are unable to carry nutrients to the plant. An over-watered plant will show stunted growth, and beginners can sometimes misdiagnose this as a nutrient problem, causing them to compound the situation by adding nutrients—and more water—to an already suffocating plant and quite literally drowning it.

A good solution is to weigh your plants with their pots dry (after repotting, for example), add 5% or 10% to that weight, and use that number as a reference for when you need to water. Some manufacturers suggest watering plants with 20% of the volume of their containers. For example, a plant in a 3-gallon pot needs about a half-gallon of nutrient solution for every watering.

It’s important that your roots have a period of relative dryness before they’re watered again. If you’re watering an outdoor guerrilla grow of auto-flowering plants, I suggest adding a drop of unscented dish soap per liter of water or nutrient solution. This aids in absorption and keeps the liquid from pooling at the top of your grow site.

6) Feed your plants lightly.

Use organic nutrients (it’s harder to overfeed with natural ingredients), and remember that auto-flowering plants prefer light feeding in comparison to their photoperiod-determined counterparts. I’ve experienced issues a number of times with over-fertilized plants, but the most severe cases were always with the autos.

Given their smaller and more fragile root structure, auto-flowering plants can handle only half the usual feeding regimen of regular plants, which develop larger root systems. In a well-aerated “living organics” medium (one that contains beneficial bacteria and compost with humic and fulvic acids), your short-lived autos shouldn’t need much feeding anyway.

Some boosters can be added to enhance root production, and many of these are available in grow shops. Here in Europe, many growers prefer House & Garden Roots Excelurator. If you have the space, a compost-brew juice aerated for 24 hours will give your plants a good boost.

7) Pinch and prune early, if at all.

Regular plants should only be pinched and pruned during their vegetative stage, and this rule applies to auto-flowering plants as well. Because the window in which to bulk up your autos is small, choose when to employ these techniques wisely. If your strains start their flowering stage super-early or didn’t get a strong start to life, you should avoid pinching and pruning altogether.

For plants that have a longer flowering time, it is possible to pinch or prune—or, even better, to use a less traumatic technique such as LST (low-stress training) early on. Use fishing weights to weigh down the branches and expose the lower areas of the plant to light. You can also bend the branches carefully to get them more horizontal. Always remember that auto-flowering plants have a brief lifespan and won’t recover well from stressful situations. It’s wise to experiment with pruning regular plants before trying it on your auto-flowering ones.

8) Harvest sequentially over time.

With all marijuana plants, the main tops are harvestable before the lower parts of the plant. If possible, wait six to 10 days between your first harvest of the main or top colas and the rest of the plant. This will result in added weight, stronger effects and better quality overall.

As they approach harvest, your plants must be closely monitored. Pay attention to the trichomes and take into account that wind, cold and heat can affect them outdoors. Exercise patience—a good rule of thumb is to give autos a week more of flowering outdoors than in, and don’t rely solely on the breeder’s recommendations for flowering times. For example, an early spring grow will slightly lengthen the plant’s maturation schedule because the hours of sunlight are still increasing, and the plants feel it. If you plant them after the summer solstice, you will notice a shorter flowering time by a week or two.

9) Grow organic.

Conventional agribusiness has a typically short-term view on how to feed plants: by bombarding their roots with salts and minerals that can be absorbed quickly. With synthetic nutrients, over-fertilization is a real possibility, leading to serious problems and toxic soil.

Organic nutrients are of a higher quality than synthetic nutes, and a living soil stimulates the plants’ digestion process, making nutrient particles more available to the roots. It’s typically also harder to over-fertilize with organics because they’re milder and more forgiving.

Your final product will burn a lot smoother if grown organically than if overdosed with mineral salts, especially if the plants are also given a good flush in the final week or two using pH-stabilized water with enzymes or a diluted compost juice. These days, a lot of organic nutrients are available on the market that contain extracts of seaweed, guano, molasses, cane sugar, coconut juice and worm compost. Also, it’s always best to start with an organics-rich premixed soil.

10) Prepare your next grow.

At 50° north, you can harvest at least twice outdoors with auto-flowering plants, but only if you’ve started your second batch of seeds 20 to 30 days before your first harvest. This way, if you harvest your plants before mid-June, the seedlings you sprouted in mid-May will ripen before the end of summer (i.e., between the last week of August and the first week of September).

With a greenhouse, you can even attempt a third grow in northern latitudes. Sprout these seeds at the beginning of August, plant them in the greenhouse when the second grow ends (around the beginning of September), and then harvest before the middle of November. The greenhouse enclosure, if well vented, will keep these plants from suffering from nature’s usual end-of-season tricks—mold, high humidity levels and early frosts.

Have fun and good growing!