In the last Planted Aquarium Care Article I discussed lighting. Although lighting is the most obvious factor contributing to aquarium plant nourishment, there are other factors to take into consideration when adding live plants to your aquarium.
In this addition of the Planted Aquarium Care series, I’ll talk about substrate – the pebbles, gravel, or sand at the bottom of your aquarium – and how your choice of substrate significantly affects the wellbeing of your plants. In particular, I’ll explain why the health of your plants’ roots is affected by the quality of your aquarium substrate.
Apart from moss, all true plants, including ones for the aquarium hobby, transport nutrients internally by way of a vascular system – one composed of xylem and phloem. Notice the distinct sections of xylem and phloem in the below cross-section of a plant root.
While the phloem transports most notably sucrose produced during photosynthesis mainly in the leaves down throughout the rest of the plant, the xylem transports water and soluble mineral nutrients (ones absorbed by the roots) upwards and throughout the plant. Hence, the plant leaves and roots are co-dependent upon one another: The leaves provide the plant (including the roots) with sucrose, while the roots provide the plant (including the leaves) with water and mineral nutrients.
Well, because of the particular function of the xylem, the health of plant roots is absolutely vital for the wellbeing of the plant as a whole. After all, the roots absorb the nourishing water and minerals that the xylem transports throughout the plant. Hence, in addition to adequate lighting, a healthy and full root system makes for green, vibrant, and full foliage.
And that’s exactly why choosing the right substrate for your planted aquarium is so important.
Before I discuss why grain size affects the health of roots let me make this one point: Aquarium plant roots are extremely delicate!
You may think that this is not the case when witnessing an aquarium shop seller tear through the thick jumble of roots in order to remove the plant from its home at the aquarium shop. But, keep in mind that those most visible thick roots you see are the primary roots – roots which are hardly responsible for water and nutrient absorption!
In fact, it is the secondary roots (also termed lateral roots), which sprout from the sides of the thick primary roots, that are responsible for the majority of nutrient uptake. And, these secondary roots are much, much thinner than their primary counterparts and are far more delicate.
Since the secondary roots which significantly contribute to the health of the plant are extremely delicate, they are very susceptible to physical damage – to damage caused not only by the plant’s physical removal from the pet shop aquarium, but also by the shifting of large sized pebbles in the home aquarium substrate.
For this reason, I feel that the smaller the grain size of the aquarium gravel, the healthier the root system will be. Indeed, very fine gravel and sand shifts significantly less than does large grained gravel and pebbles.
Especially when using a gravel vacuum (by the way, you should gravel vac areas around plants only VERY gently), large grained substrate moves around a whole lot …even in the areas of the aquarium that are not being gravel vacuumed.
Imagine the damaged sustained by the secondary roots when pummeled and pulled by a 2 inch deep and tumbling layer of large pebbles! Now fathom the plant roots having to suffer this abuse on a continuous weekly or biweekly basis (and, even when you’re not gravel vacuuming your aquarium, large grained substrate does tend to shift)!
That said, how in the world can you expect the secondary roots to keep up with the sustained physical damage, and, consequently, why would you expect the roots to support a full foliage if you place the plant in large grained substrate?
The good news is that you can easily alleviate the above mentioned problem by simply using fine grained gravel, or even sand (intended for freshwater aquarium use), as opposed to bulky gravel or pebbles.
In fact, fine grained gravel not only provides your aquarium plant roots with a stable environment, but it also offers far more surface area for biological filtration and looks much nicer too.
When I switched over from regular sized gravel to sand in 2006, my aquarium plants displayed an explosion of growth! I witnessed a huge and visible benefit to the health of my plants literally within a week and a half! They grew to a much larger size, became fuller, and turned greener, and the only change I made was to replace the normal sized gravel with sand!
Although some of my readers may be concerned with the development of oxygen starved (anaerobic) zones within the deepest layers of the sand substrate, keep in mind that 1) I only keep the sand layer deep in the parts of the aquarium nearest to the plants, and that 2) the roots actively pull water through the substrate anyway.
In fact, after I added the sand to my aquarium, the plant roots expanded to such a great extent that even the thinnest layer of sand in the front of the aquarium is inhabited by a shockingly dense patchwork of roots.
So, if you want to take it one step further and add sand instead of fine gravel to your planted aquarium, I say go for it! Also, if you have any questions about my aquarium setup, feel free to post them in the comments section below.
Take care, and happy fish-keeping!