Using rainwater to water your container grown plants will help keep them happy and healthy.
For Beginners: If you are new to container gardening, I highly recommend buying a good potting mix to start with. Miracle Grow Potting Mix is usually good quality and will feed your plants for about 4-6 months. When plant growth starts to slow, I recommend adding Osmocote Plus to the potting mix as recommended in the instructions. Osmocote Plus does not contain any calcium. You can add calcium by adding limestone or gypsum (1 teaspoon per gallon of potting mix). Sprinkle the calcium evenly over the top of the potting mix, then water it in. Use limestone ONLY if you need to raise the pH of the media. Use gypsum if don’t need to change the pH. See below on how to test pH. You can buy limestone and gypsum in small quantities online, or you and buy them at any garden center usually in a large 50 lb sack. If your plants go dormant in winter, remove most of the Osmocote from the top container a few weeks before the first frost. Feeding your plants when they are dormant may cause them to wake up and grow at the wrong time. This can damage or kill them.
Growing Media: 2 parts Sphagnum peat moss, 1 part perlite. See below for more info.
Media pH: 5.5-6.2. See below for more info.
Nutrient Mix: Full strength =38 ml of each stock per gallon. Half strength = 19 ml of each stock per gallon. For large fast growing plants, use full strength solution twice a week and Nitrogen Booster (4g/gallon) once every other week. Another option is half strength solution twice a week and Nitrogen Booster (4g/gallon) once a week or every other week – I recommend this as a good starting point. House plants can use half strength once a week or two weeks and Nitrogen Booster 4g/gal every two weeks. Succulents and Cacti are fed infrequently, maybe half strength once per month depending on species. The easiest way to feed is by filling a watering can with rainwater then adding your stock A and B to it. How often your feed is determined by a few factors like how fast you want your plant to grow, the quality of your potting media, and how often you water. A quality potting media should be able to catch and hold the nutrients in the rootzone. This is called cation exchange capacity. If it is hot and you are watering all the time, you may be leaching the nutrient out the bottom of the pot. If this is happening, put your plant out of the afternoon sun during the hottest part of the year.
Mixing a Potting Soil: There are many different ingredients that can be used in a potting soil. Peatmoss, sand, perlite, vermiculite, composted wood products, and rice hulls are a few commonly used. If you are starting out, I recommend using sphagnum peat moss mixed with horticultural grade perlite. Both are usually available at your local garden center. Mix them at a 2 to 1 ratio. You want a potting media that holds water but doesn’t stay too wet or dry out too quickly. If the media is holding too much water, add more perlite. If it is drying out too quickly, add more peat moss. I use a 2 parts peat moss to one part perlite. Thats what works for my climate. Mix them together on a flat surface. Do not breathe in any dust from the perlite or get it in your eyes. Add water too it to control the dust. Water your new potting media before adding it to the pots. When peat moss dries out, it can be hydrophobic and difficult to get properly wet, especially when it is in a pot. You can use the same media for 2+ years.
Media pH Control: Peat moss is naturally acidic and may need to have the pH adjusted. A pH of 5.5 to 6.2 is acceptable for most plants grown in containers. Most can live outside this range and still be healthy. Add 1/4 oz to 1/2 oz (about 1 teaspoon) of limestone per gallon of media to raise the pH to an acceptable level. This can be done while mixing the media, or add it to the top of the media while it is in a pot and watered in. Finely ground dolomitic or calcitic limestone can be used. Both are usually available at any garden center.
Testing Media pH:
- 2-1 method – Mix 2 cups distilled water with 1 cup potting media. Stir well, then let it sit for 1 hour. Test the pH of the water. I usually use API Wide Range pH Test Kit. It’s for aquariums, but it still works.
- Slurry Method – Take a 1 cup sample of the potting media. Slowly water it with distilled water until it is fully saturated, but the is no runoff. Insert a pH probe to attain pH.
Testing Container Runoff – The day after feeding and while the media is still quite moist, water one of your plants with distilled water until water starts coming out the bottom. Catch some of the runoff in a clean cup, about 30 to 50 ml. Test the water with a TDS meter(500 scale). If the runoff is above 500 PPM is could be sign you are over feeding, and excess nutrient is being lost out the bottom. I usually try keep the runoff in the low 300’s or less. It’s a good sign the plants are consuming the nutrients and the media is holding on to it. You can also test the runoff’s pH and it should give you an idea of the pH of the media.
How to Water: Use the 110% rule when watering. Water until the media is 100 percent saturated. Add an extra 10 percent that will come out the bottom of the pot as runoff.
Repotting: Gradually increase pot size as your plants grow. This will help save water and nutrients. Repot when the roots have filled the container and hold onto the growing media. Loosen the roots slightly if they are beginning to tangle.