Most of the time we strive to grow our plants as fast as genetics will allow. Faster growth from the start means more growth sites and fuller plants with less chance for pathogens and bugs to creep in, leading to the biggest yield in the fastest time.

Many people start their seedlings in a small vegetative area then grow them until the desired size is reached and the plants can be transplanted into a larger flowering/fruiting area. But what if you need a break from your schedule? How do you stop your vegetative seedlings running amok, and outgrowing their kindergarten stage too quickly?

Occasionally, life throws a curveball that affects a grower’s schedule. From moving houses, experiencing an illness, getting in an accident, taking a holiday, or fixing equipment failure, there are lots of reasons why a grower might need to temporarily slow down plant growth.

A gardener friend of mine has limited space and grows his seedlings in a small cupboard before transplanting into his main garden. A little while ago, just as his plants were ready to be transplanted and triggered to flowering, he was in a car accident that meant he would be unable to tend to his much larger, flowering plants for a few weeks. Limited mobility meant he couldn’t clean and set up the hydroponic system, and he didn’t have anyone he was able to ask for help. The seedlings were now pretty large and ready to outgrow their vegetative area. He needed to put the vegetative plants in low gear while he recovered, and he did so using the following three easy steps.

One: Keep Plants Healthy

It’s important to keep your plants healthy. Methodically go through each one, removing any dead or sick-looking leaves. Check the roots, and if there is any pythium (root rot), remove these brown bits. Hopefully you won’t need to do either of these treatments, but if you must, then give them a little dose of a gentle vitamin stress buster afterwards to help them recover. If the facilities are available, a good spray of ozonated water can really help disinfect the leaves and roots of the plants as well (see “Ozone: A Growroom Super Hero” in Maximum Yield January 2014, available online).

Once plants appear healthy, cut the nutrient EC of the feed. Of course, each plant is different, but just for example, let’s say you are currently feeding veg nutrients to an established plant at 1.6 EC and pH 5.5. I would suggest dropping the EC down to about 1.2 or 1.3. This will slow the fast pace of growth, but if you slow the plant’s metabolism down in other ways too, you won’t get a deficiency.

Stop feeding any high nitrogen boosters or growth hormones. Stick to just the basics of your full-spectrum balanced feed with no growth additives—the additives work best when everything else is optimized, so for our current situation of slow growth, additives would be equivalent to putting a turbo on a car with bald tires.

Two: Lower the Temperature

The second big adjustment is to lower the temperature. Most popular hydroponic plants grow fastest in temperatures of around 70 to 80°F in the day, dropping by preferably no more than 10°F lower at night. Because we are looking to slow the metabolism and limit fast growth, we can drop the temperature down to about 60°F during the day and a little cooler at night. This will slow growth considerably, but don’t worry, it won’t actually hurt your plants. They can take it.

Three: Reduce Light Intensity

The third biggie is light. It is important to stick to your current light and dark timing schedule (usually 18 hours of light, six of dark for vegetative growth), but the available light intensity will need to be reduced, which will help slow down growth. If the light was reduced without also having lowered the temperature and feed EC at the same time, then the plants would stretch considerably.

This is why it is important to do all these steps concurrently. It is still important to spread the light out evenly over your plants, as you don’t want any in shade, but you are looking to reduce the overall lumens reaching them by around half.

Depending on what the set-up is like, some growers may be able to switch off some lights, or, alternatively, growers can raise the lights up higher above the canopy, thus achieving the same reduction in available lumens.

Don’t raise the lights too far, though, as light intensity and distance follows an inverse-square law, which means that when the distance from light to plant is doubled, the plants receive only a quarter of the available light intensity.

Additional Tips

These three steps will slow plant growth considerably and will allow growers to put the veg on hold for a few weeks without any long-lasting damage to their plants. Another good idea to halt growth is to pinch out the growing tips. The plant will take a couple of days to catch up and force growth out laterally. It is likely this is already being done in combination with other techniques, but it can also be used to put vertical growth on hold for a little while.

Make sure to keep an eye on the plants during this time. Don’t neglect the roots and watch out for pests. Longer in veg means longer for problems to develop, so keep up basic growroom hygiene and maintenance as much as possible. My friend who had the car crash put his veg plants on hold for more than seven weeks using these techniques. There were no complications, deficiencies or stretching, and his plants are healthy, growing at their usual fast rate again now.

Once ready to get the plants back into their full-speed growth regime, it is as simple as going back to the usual growing routine—bring the light intensity up, raise the heat and raise the nutrient EC back to normal over the course of a few days, then start introducing boosters again. Plants will adapt, and you will be back to your usual schedule in no time.