That's why I've compiled this short list of 5 "outside-the-box" ways to help speed up the process. Note: I haven't tried these methods (except 4 and 5), so try them at your own risk.
1. Give your plants vitamins.
As strange as it sounds, vitamins contain substances that plants need. Simply take a multivitamin tablet (1-2 per pot) or several for a large garden and grind them up using a pestle or knife handle. Then, simply spread the powder in the soil of your plants and water. Repeat every 2 weeks. Source: https://youtu.be/bnE4A6U91ik
I haven't tried this method. My thoughts are that the success of this depends on what is in the vitamin and how it's made. Synthetic vitamins often have chemicals that are not necessarily good for humans, let alone for plants. My second concern is cost. If you have more than a couple of plants, you'd have to crush a lot of vitamins to get enough powder to cover your garden. At that point, you're better off just using fertilizer.
2. Water with Club Soda
My first thought when I saw this was, "what, no vodka?"

You can check out the full article here: https://lifehacker.com/water-plants-with-club-soda-to-make-them-grow-faster-an-1567061455
3. Waiting for the worms
Worms are nature's composting army. As earthworms burrow through the soil, they eat and digest dead plant and animal material. As they defecate, they leave castings that are extremely dense in minerals and microorganisms that are beneficial to plants.
There are a few ways to benefit from these critters. First, you can buy several hundred earthworms in a bait or natural gardening store. Then, simply turn them loose in your garden. Second, you can put them in a bed of dirt and add leftover material from your composter. Sometimes, the bacteria that break down the food and other materials in your composter can create substances that are toxic to plants. By allowing the worms to eat through the soil with these materials, they can break down the toxins and leave a nutrient-rich, non-toxic soil for your garden.
The third and easiest way to benefit from worms is to buy pre-packaged worm castings from a reputable store. Call around for prices or look online, but it will save you the trouble of dealing with the worms directly.
4. Talking and Singing to Your Plants
This method was popular in the sixties and seventies. There were a few studies done in this regard by researchers at Penn State and in South Korea. Dr Rick Marini of Penn State suggests, "wind or vibration will induce changes in plant growth. Since sound is essentially vibration, my guess is that vibration is causing a response."A paper in 2007 from scientists at South Korea's National Institute of Agricultural Biosciences noted that two genes responsible for plant response to light —known as rbcS and Ald— were turned on when exposed to sound at about 70 decibels.
Dr Marini stopped short of endorsing sound as a definitive influence on plant growth, but hey, if you're practicing for your next American Idol audition, do it in your garden. Your plants may grow faster.
Source: http://news.psu.edu/story/141343/2008/08/25/research/probing-question-does-talking-plants-help-them-grow
5. Use Miracle Plants device
Miracle Plants is a device based on similar technology to the sound stimulation in #4 above. Mr Fulvio Balmelli, a medical researcher in Italy, studied the biological processes in plants and discovered specific frequencies of vibration that cause plants to grow healthy and strong. From this research, he created the Kyminasi Plants frequency technology.
Early tests of this technology show improved pest resistance, faster growth times and increases in crop yield by weight of up to 70%.
Miracle Plants is the consumer product of this technology and is suitable for gardeners and small farmers of up to 3/4 of an acre. Final testing of the larger devices for commercial agriculture is ongoing and should be available soon after this writing. For more information about Miracle Plants, go to www.gardenersareawesome.com
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Honorable Mention: Use coffee grounds as a fertilizer

You can get used coffee grounds from your local Starbucks or other coffee house for free usually. This is a waste product for them.
If you've had trouble growing plants in your garden in the past, check out some of these tricks. They may be able to turn your thumb green!