If you caught our last blog post – SEED STARTING MIX: WHAT IS IT AND HOW TO MAKE IT? you know that there is a difference between seed starting mixes and potting mixes. You also learned how to inexpensively make your own seed starting mix! Both seed starting mixes and potting mixes are important and they both have their place when it comes to gardening. Both mixes can be purchased at most farm and garden centers, and big box stores, you can also easily (and inexpensively) make your own.
Ok, so what’s the difference and when should you use a potting mix / potting up mix / potting soil? With so many brands, types, and varieties available at your garden center, it can quickly become overwhelming and make your head spin. At a high level, seed starting mixes are for starting seeds and not for prolonged growing. It’s has a fine texture, is light, fluffy, and typically does not contain any actual soil or compost. The ingredient list is short and usually contains peat moss and/or coco coir, vermiculite, and perlite. It’s light weight, in order to not weigh down germinating seedlings, and does a great job at retaining water. Potting mix or potting soils are denser, will have a coarser texture, and typically contains compost or soil, along with peat moss and/or coco coir, vermiculite, perlite, and will oftentimes contain fertilizer.
For best results, use your seed starting mix to start and germinate seeds. Your potting mix/potting soil should be used for transplanting seedlings and growing plants in containers. If you want to know if you can streamline and only use potting soil, the answer is technically yes. Your seeds will need to work a bit harder to push through the coarser and denser soil and too much fertilizer can harm tender young seedlings.
Most commercial and homemade potting soils will contain a blend of the following ingredients:
While peat moss is a heavy hitter and in a majority of seed starting and potting mixes, there is some controversy around its use. Peat moss is partially decomposed Sphagnum Moss. In the United States most peat moss comes from Canada, it’s considered a renewable material, however it’s harvested from bogs and grows at a very slow rate. Peat is stable, acidic, takes a long time to fully break down, is widely available and inexpensive. It helps to bulk up mixes, it’s light weight, and does a good job of retaining water once wet.
Peat moss will help to aerate the roots of your seedlings, drains well, but is also very low in nutrients. Since peat moss is acidic (it has a pH of 3.5 to 4.5), it’s a good idea to add some limestone to peat based mixes to help balance out the pH.
Also another heavy hitter and found in a majority of seed starting and potting mixes. This material is actually a by-product of the coconut industry! It’s comes dried in compressed bricks that need to be wetted prior to use – Coco coir can absorb up to 10 times its weight in water. Coco coir helps to provide structure, it’s lightweight, has good drainage and aeration. After coconuts are harvested, everything in between the hard shell of the coconut to the outer coating of the coconut seed is considered coco coir. That material is then furthered processed into the classic coco coir that we use. Similar to peat moss, coco coir lacks nutrients and using this material alone won’t support growing plants.
Perlite might look like and feel like small white balls of Styrofoam, but it’s actually a mined volcanic rock. When this material is heated to high temperatures (1600 degrees F/ 871 degrees C), it expands to 13 times it former size, making it both lightweight and sterile. This material is porous and can hold three to four times its weight in water. Using perlite in your mixes will help improve drainage and also increases pore space. It’s great additive that is easy to find in stores or online.
This material is also mined and then processed, it’s a naturally occurring mineral that is heated until it expands. This light weight material will add calcium and magnesium to your mixes, will help with porosity of your mixes, and help with water retention. Since it’s heated, it’s a sterile material, that is non-toxic and has a neutral pH. Using this material will improve aeration and moisture retention, which translate to your seedlings having a healthier root system that is better able to spread out and absorb nutrients. This in-turn will result in a healthier and lusher plant.
This glorious amendment is used to improve soil and fertilize, made from decomposed organic materials, it’s teeming with life and contains billions of beneficial microbes. Compost is nutrient rich, has excellent water retaining capabilities and is a wonderful addition to DIY potting mixes. Not only is compost wonderful as an additive for potted plants, it’s also can drastically improve fertility in your home garden. When making your own potting soil you can either use your own homemade compost or pre-made bagged compost.
Coarse sand can be added to improve drainage and add weight to you mix. If you’re mixing potting soil for succulents or cacti you will want to add sand to your mixture.
Use this when you are making a peat based potting mix, it will help level your pH and combate the acidic nature of the peat moss. Limestone is a mineral that is mined from natural deposits. Limestone is inexpensive and readily available, we recommend Jobe’s brand. A little bit of limestone goes a long way – you’ll only need to add about 3 teaspoons for every gallon of peat moss that you use.
You’ll want to add fertilizer to you coco coir or peat moss based potting mixes, since they are nutrient poor, your plants will benefit from the extra additives. If using a commercially prepared organic granular fertilizer, you’ll want to add approximately 4 teaspoons for every gallon of finished potting mix – Dr. Earth, Plant-Tone, and Jobe’s are all good recommendations.
Making your own DIY potting mix:
- 2 parts coco coir or peat moss
- 1 part perlite
- 1 part vermiculite
- 2 parts compost
- 4 teaspoons of granular fertilizer for every finished gallon
- 3 teaspoons lime for every finished gallon (if using peat moss)
A part is just an equal measurement – as long as your consistent, you can use anything you have on hand, a cup, a scoop, a bucket, or even whole bags.
When making your potting mix you have control over the additives and the quantity, if you’re potting up a large number of seedlings, or have large planters to fill, you’ll want to mix up a large quantity. For large quantities blend it up in a wheelbarrow, for smaller amounts use a large pot or bucket, any clean, dry container will work.
If you made our DIY seed starting mix and have leftovers, you can save it for next year or use it as base for making potting mix
- 1 part leftover DIY seed starting mix
- 1 part compost
- 4 teaspoons of granular fertilizer for every finished gallon
3 teaspoons lime for every finished gallon (if using peat moss)
Mix it up and you’re good to go. It’s that easy! Happy Planting!
Until Next Time…