The primary problem with compost, peat, or coir-based potting soils is that they are very water retentive right out of the bag and they become MORE water retentive as the particle size breaks down after planting in them. Compost based soils are not a good choice because if you water properly (so that a good portion of the water you applied exits the drain whenever you water) the soil retains so much water that it creates anaerobic conditions and roots die or rot. If you DON'T water properly, salts accumulate in the soil and slowly kill the plant. Mixing it (compost) with another fine product like peat or (sterile) seed starting mix doesn't do anything to solve the problem.

If you mixed 1 part of compost with 5 parts of pine bark fines and 1-2 parts of perlite and a little garden lime, you would have a very good houseplant soil, but there are still soils even better than that you can easily mix yourself, if you're willing to go to a little effort.

Al

i'm all ears.....er....um eyes....

You'll find the open end of a long discussion about container soils for houseplants, here.

You'll find the same original post here, but lots of additional conversation on the same topic.

The basic soil requires you to find a few ingredients, but once located, you'll be able to build a soil less expensive than commercially prepared soils, but more importantly, a soil that is far more forgiving and much easier to grow in. I promise your plants will love it - especially if you cultivate a couple of very basic fertilizing and watering habits.

Al

West, 'in my older plant books,' authors recommended using compost in certain house plants. Ferns are one example. Nowadays, there are other mediums that takes the place of compost. Offhand, I can't recall what they are..lol.

If I ever decided to use compost, 'yuck' mice, spiders and worms, lol, it would definately need baking..Use a disposable pan, bake at 375 for 40 mins..But I must warn you..it stinks up the house..lol..Still, if you feel a need to use it, it's worth the odor..
I baked soil many times, 'in the past' so believe me, I am familar with the smell. lol.

I don't know if it was you who mentioned manure. If you use it, the manure should sit at least 1 yr..fresh Manure WILL burn roots. Do you plan on adding compost/manure to your indoor plants? If so, which plants? Toni

As noted, compost is a poor choice as any significant fraction of a container soil because of its fine particle size. Trying to amend it with products like perlite is like trying to amend pudding with perlite. Perlite does not change the drainage characteristics of compost, only the total volume of water the compost holds. If you start with a given volume of compost and add even as much as an equal volume of perlite to it, the perched water table remains at the same height and aeration remains minimal.

Manure is also a poor choice in container soils. It is extremely high in salts, it clogs air pores as it very quickly breaks down into sludge, and it's high N content makes it very difficult to add enough fertilizer to satisfy the plant's needs for other nutrients w/o elevating o/a fertility levels higher than favorable. It simply provides NOTHING in the way of nutrients you can't get in a good fertilizer and is a structural disaster, presenting a laundry list of issues to be dealt with.

Al

Compost used indoors is not the best of ideas, it won't have the opportunity to interact with other things of nature (germs, microbes maybe) which it would if used as an amendment in outdoor plantings.

If anything, I've used Worm Castings (earthworm poop) collected for this purpose. The recommended amount was something like 1 Tablespoon per pound of mix. I think I used a bit less (2 tsp per lb. of mix). The plants perked up nicely.

1 part turface
1 part soil conditioner
1 part grani-grit (growers)
1 tsp. epsoma lime granules

is that what i was supposed to get from that? lol
the soil conditioner would be fine pine bark mulch??
where can i get granigri and turface???

Scratch the lime and use gypsum in the gritty mix.

If I knew where you live, I might be able to help with the 'where' part. The bark is best if it's main fraction is very close to the 1/4" size range or slightly smaller (1/8-3/8) and uncomposted.

Al

Thank you so much Al. I just found this houzz website which is really helpful. Thank God that you I find you everywhere Al! I also found you in Reddit. I did the gritty mix you recommended, but I had to mix some soil in it because this mix wasn't working for some of my non-cacti plants and I didn't really know how often to water these. I live in NYC in a sunless apartment. I am beginning to find so much peace and joy in having plants that it's becoming my favorite hobby at my senior age. However, I'm just learning from trial and error. When I mixed your gritty mix in my organic soil mix I found that the water does drain out fast. However some of my cacti, they're not doing so well. Not sure what I'm doing wrong. I think I still over water them and kill them. not sure how often to water them with the gritty mix. I found that when I let the mix sit in water for a while they do retain a lot of water especially in the bottom. So I'm confused. I have them in two separate containers and the one I don't water often is doing great. I used the Greenway Gypsum Enzley recommended in Reddit when I first made the gritty mix. However, the cacti that I water less frequently are doing fine. However, I think my problem is that some succulents (cacti) have very tiny roots and I don't know exactly how to plant them inside the gritty mix so that they can absorb water and I end up over watering, anyway. If you have any experience with small rooted cacti and how to plant them, please HELP! TYSM, I also am having problems with my Sanseverias I planted with the gritty mix. I don't know how often to water! :( When I first planted them a few weeks later I saw the most beautiful roots growing when I pulled them out to see if they were rotting. But now I don't know how often to really water them. It's hard to tell with the gritty mix. I don't want them to die!

Al TY so much for your expertise and advice on this matter.

You're the greatest!

Loyda

If they're small rooted, use equally small containers. Water when needed (which is probably rarely), based on their native habitat.

TY Dbarron. I will probably have to change their home. It is too large. Thank you so much. But now I have pests; gnats. I have Thuricide. I really hope that helps. They came in with a plant I got. I couldn't identify which plant it came with so I couldn't isolate them! :(. Lets hope the neem oil and Thuricide helpls. I read that the trick is to be persistent and not give up. I also orderred some of the little yellow sticky sheets. If you have any recommendations, please let inform me. Have a great weekend!

If you eliminate peat based soils and get watering under control, gnats will usually self-eliminate (or mostly).

Thank you Loyda, for your very kind words.
Let me start by noting it's possible to take a number of ingredients from which an exceptionally productive medium can be made and combine them in such a way the product would be considered unusable by most growers. The size of the particles, How much variation there is in the size of the particles, and the ability of the particles to hold water within the particles all factor into how much air and water the soil can/will hold. Plenty of growers read about the gritty mix here at GW and decide to make it themselves. If they can't find materials to make the original recipe, they often make unsuitable substitutes, which often leads to issues requiring work-arounds. I'm guessing that's where you are now.

I have about 100 plants (mostly bonsai, potential bonsai material, and succulents) in my basement under LED lights where I control light duration, temperature, and relative humidity. I water on a schedule. About 3/4 of my plants, those in larger pots, get watered every 6 days, religiously. The others are watered on a 3 day rotation because they are bonsai or started cuttings in very small containers - some in plastic medicine containers. It's often said you should water ONLY on an as needed basis, but that rule was written or repeated by someone whose experience was limited to media that was so water-retentive and unforgiving, watering on an as needed basis was the only way to avoid root issues related to over-watering. All or nearly all water that might 'perch' in media more water-retentive should drain completely from the gritty mix. Adding fine material to the gritty mix for more water retention, practically speaking, negates the very reason for making and using it. If the gritty mix is made from appropriate ingredients of an appropriate size, you can very easily change the amount of water it holds by varying the ratio of grit to Turface; and this is done without introducing a perched water table.

I have always mentioned that the most important contribution I make to the conversation about container media is not the recipe. By far, it's providing an understanding of how water behaves in container media. Understanding WHY the gritty mix works so well will give you the flexibility to make decisions about substitutes and tailoring the mix to suit your unique set of circumstances or a particular plant.

I encourage you to try to make some time toREAD THIS. If you do, when you get to what looks like the end of the post you'll see a live link that says "see 509 comments". If you click on that, the rest of the thread will pop up. I need to repost it because folks are generally missing 2/3 of the post now.

I am beginning to find so much peace and joy in having plants that it's becoming my favorite hobby at my senior age. However, I'm just learning from trial and error. Keep having fun, but try to avoid learning by trial and error. It's a painfully slow way to learn. Learn all you can from a trusted source, then use your practical experience to validate what you learned. You'll be amazed at how far/fast that will take you along the path to a green thumb.

I think my problem is that some succulents (cacti) have very tiny roots and I don't know exactly how to plant them inside the gritty mix so that they can absorb water and I end up over watering, anyway. If you have any experience with small rooted cacti and how to plant them, please HELP! With a well-made gritty mix, you can use much larger pots than you would be able to if you were using a water-retentive mix. There is virtually no such thing as over-potting if you're using a medium that doesn't hold perched water. Tease the old soil out of the root mass - prune roots if necessary. Partially fill a pot with gritty mix. Leave enough space so the bottom of the root mass rests on the new gritty mix and the top of the root mass is 1/4-1/2" below the rim of the pot. Add to a separate mixing bowl or tub, enough gritty mix to fill the rest of the remaining pot space to the level of the uppermost roots. Add some vermiculite or a little peat to only the soil in the bowl/tub. Mix it together and add a small amount on top of the soil in the pot and mix it lightly into it, that would be the main soil mass. Add the plant and back fill.

When I start a cactus or succulent and want to provide some water to the roots w/o wetting the entire soil mass, I use a hand spritzer adjusted to provide a coarse spray that's almost a stream. I use only what I estimate to be enough water to moisten the soil down to the bottom of the root mass. Of course, some of the water will move down into the soil below the root mass, but thinking about moistening the top inch or two of soil with a spritzer is usually enough to keep me from over-watering new or semi-dormant transplants.

I also am having problems with my Sanseverias I planted with the gritty mix. I don't know how often to water! :( When I first planted them a few weeks later I saw the most beautiful roots growing when I pulled them out to see if they were rotting. But now I don't know how often to really water them. It's hard to tell with the gritty mix. I don't want them to die! When roots have colonized the entire soil mass, you can use a wooden "tell" to "tell" you when it's time to water. See below for info about a tell. It's not that easy if it's a fresh transplant because the soil particles are fairly unstable and tend to make it hard to insert a tell. So, when you establish the planting, put 1/2" of soil in the pot bottom. Put a drinking straw or other straight tube on top of the 1/2" of soil so it's vertical or it follows the sidewall of the pot. Cover the top hole to keep soil out and make your planting. When you need to use the tell, it will slip right through the straw to the bottom of the pot. Pull it out and 'read' the tip. If it shows moist (for sans), withhold water until it shows dry. Then, water thoroughly.

All the comments or suggestions I offer about the gritty mix are with the assumption the mix you're using does what it is originally designed to do - hold an adequate amount of water w/o supporting perched water, and provide you with adjustability. If what you're using won't do that, we'll need to talk about some sort of work-around or fix for issues that concern you.

Using a 'tell'

Over-watering saps vitality and is one of the most common plant assassins, so learning to avoid it is worth the small effort. Plants make and store their own energy source – photosynthate - (sugar/glucose). Functioning roots need energy to drive their metabolic processes, and in order to get it, they use oxygen to burn (oxidize) their food. From this, we can see that terrestrial plants need air (oxygen) in the soil to drive root function. Many off-the-shelf soils hold too much water and not enough air to support good root health, which is a prerequisite to a healthy plant. Watering in small sips leads to a build-up of dissolved solids (salts) in the soil, which limits a plant's ability to absorb water – so watering in sips simply moves us to the other horn of a dilemma. It creates another problem that requires resolution. Better, would be to simply adopt a soil that drains well enough to allow watering to beyond the saturation point, so we're flushing the soil of accumulating dissolved solids whenever we water; this, w/o the plant being forced to pay a tax in the form of reduced vitality, due to prolong periods of soil saturation. Sometimes, though, that's not a course we can immediately steer, which makes controlling how often we water a very important factor.

In many cases, we can judge whether or not a planting needs watering by hefting the pot. This is especially true if the pot is made from light material, like plastic, but doesn't work (as) well when the pot is made from heavier material, like clay, or when the size/weight of the pot precludes grabbing it with one hand to judge its weight and gauge the need for water.

Fingers stuck an inch or two into the soil work ok for shallow pots, but not for deep pots. Deep pots might have 3 or more inches of soil that feels totally dry, while the lower several inches of the soil is 100% saturated. Obviously, the lack of oxygen in the root zone situation can wreak havoc with root health and cause the loss of a very notable measure of your plant's potential. Inexpensive watering meters don't even measure moisture levels, they measure electrical conductivity. Clean the tip and insert it into a cup of distilled water and witness the fact it reads 'DRY'.

One of the most reliable methods of checking a planting's need for water is using a 'tell'. You can use a bamboo skewer in a pinch, but a wooden dowel rod of about 5/16” (75-85mm) would work better. They usually come 48” (120cm) long and can usually be cut in half and serve as a pair. Sharpen all 4 ends in a pencil sharpener and slightly blunt the tip so it's about the diameter of the head on a straight pin. Push the wooden tell deep into the soil. Don't worry, it won't harm the root system. If the plant is quite root-bound, you might need to try several places until you find one where you can push it all the way to the pot's bottom. Leave it a few seconds, then withdraw it and inspect the tip for moisture. For most plantings, withhold water until the tell comes out dry or nearly so. If you see signs of wilting, adjust the interval between waterings so drought stress isn't a recurring issue.

Al