I have a dwarf Cara Cara Navel, from Durlings. Because of the horrible luck I've had with four other dwarf citrus trees in my clay soil, I'm going to build an elevated box that I can fill with a soil mix of my own. But I'm not sure what the minimum size should be that would allow the tree to grow to its maximum size. I have a dwarf Bearss lime in a gallon plastic container, which measures 15" diameter and about 16" height. I'd guess I want to build something larger, 24"x24"x24", or even 36"x36"x24". It won't have a bottom so the natural soil will be available if there is a tap root.

I don't want to build a huge box, larger than necessary, so I'd like to ask for some suggestions.

jc

I would do do a gradual change in pots. From 1,3,5,7 till it gets to a good enough size for your box.

I need to build a box now, before winter comes and it's already in a 5 gallon container. So my original question remains, what's the minimum size box that would allow the full potential of this dwarf Cara Cara.

Wish I could give you the answer-- but I can't. But I can tell you generally for the most part- plants in general don't do as well when they are put into containers that are much to large for them, there are some exceptions to that, but I don't think citrus is one of those exceptions.

If you wish the tree to eventually grow close to its full potential, you will need a 36 X36 X36 box. However, as David and Fred pointed out, it would be best to grow the tree by stepping it up into larger and larger containers, before planting it in a huge box. I have a Page Mandarin growing in a 4-ft wide container, and a Satsuma in a 30-gallon container. Both trees started out in a 1 gallon, 3 gallon, 5 gallon, and then a 15 gallon before being transplanted into the 30 gallon container. - Millet (846-)

If I were to put this tree into a 15 gallon container, how long would I want it to be in there before I transplanted it to the larger box? Also, I'm curious to know what negative effects would arise from putting a dwarf citrus in a box that's too large. And isn't putting it(a young dwarf tree) directly in the ground a bit like putting it in a box/container that's too large. Or is it the synthetic soil mix(in the too-large container) that creates the problem?

Speaking of container mixes, this dwarf Cara-Cara came in a fairly heavy 5 gallon container...looks like there is gravel in the soil mix. Why would a nursery use gravel?

I would not be hesitant whatsoever to plant a 2-3yr old tree from a 3.4gallon container into a 3x3x1 raised bed (no need for it to be 3 feet tall), as you are calling it a "container with open bottom over open soil". There are very good reasons stepping up plant growth in containers, but a raised bed has different water dynamics than a regular container, i.e. less worry. With extremely fast draining mixes (not bagged soil), even when placed in typical containers, the requirement for incremental steps into larger sizes is diminished significantly.

I honestly am not sure why Millet would give such conservative advice, but if you are adamant about trying the raised bed method, I'd say go for it.

If you have had bad luck in the past growing with your clay soil (which isn't easy in poor soil) then I would put the raised bed container directly over *undisturbed* clay soil. You can use the same "good drainage" mixes that folks use for containers -- at least 50% of small/med pine or fir bark mixed with other typical container components: some which are meant to retain water, others meant to increase porosity (air) or help some with texture or reduced volume (like perlite).

A larger sized box (like 3'x) will protect the root zone from excessive heat/cold better than a smaller one. If planted in a very well draining mix, this is what I consider a fairly no-brainer and *relatively* easy way to grow citrus if your climate is appropriate.

I have even mixed up to 20% of garden soil into the mix, as it is supposed to help with the "transition" of roots from a luxury mix into the natural clay soil. I cannot attest to the truth in that, however. But if you do, do so carefully as not all clay soils are equal. The heavy clay where I live (San Joaquin Valley, CA) is a lot better quality than the clay in other CA areas, and from what I've seen and heard is very different than near-muck clay of parts of Texas.

If you do choose to mix some (don't use much) of your clay soil, let's say 10%, consider this your water retentive component and be sure any other additions to the bark+natural soil are somewhere in between (like CHC).

The reason you put your raised box over undisturbed soil is that excess water will drain out from underneath the box. As it hits the poorer clay soil a lot should runoff, so be sure there isn't a grading issue right under the box.

Eventually the organics from your raised bed mixture will start amending the soil underneath.

Are you the one who purchased Costco trees? If so, yes the W&N trees are in a very heavy mix and there are some smaller gravel parts. This is because they are field grown trees, which is why they are so big and the root ball is so dense. They use the original soil from the field and add a basic potting mixture around it. It is not meant to be a long lasting potting mix and in fact is counter-productive to keep it in a container without replacing 100% of the soil.

Keep in mind, my experience is from Zone 9. So this post is lacking the advice about fall planting with severe winter around the corner. Even our winters here have many non-rain days with good sun. But from the soil drainage perspective, the raised bed dynamics would be the same regardless of climate.

Also keep in mind, if you choose to build a raised bed but do so in another manner (like amending the soil directly under the bed, or using a heavier mix in the raised bed) you will have a more difficult time, in line with your experience of planting directly in your clay.

Forgot to add, if you are concerned about taking my advice, and decide to step up in containers, you could build the box now and fill it with a garden soil mixed with bark, and place your containers inside this temporary raised bed mix so they don't have to be taken indoors. As you step in containers, you still keep the container inside the 3x3 box. It protects the soil from excess temps and if the roots start growing out of the bottom holes, they will thrive in the soil. If excessive roots start growing external, you'd need to cut the container off in order to pot up.