Starting tubers early indoors

dahlia1972

Because I have such a short growing season here in Rhode Island, I'm starting my tubers in pots indoors this year. I've planted them in 3 inch pots with 1/4 inch of potting soil covering the eyes, and was advised not to water them at all until they grow stems. Is a 3 x 3.5 inch inch pot too small? I was told it's fine but am still skeptical, as they have 4 more weeks to grow before I plant them in the garden. The potting soil was moist but is already bone dry. Should I water them a bit?

Flowernut

dahlia1972 I pre-start all my tubers in soilless potting mix. I first moisten the mix and then use #801 and #601 insert trays that I fill with the potting mix and then place my tubers, covering them with the potting soil. As the top portion of the mixture dries I use my 2 gallon sprayer to spray the top to maintain moisture. I just pre-started a week ago and lots are already rooting.

Teddahlia

For the past several years our ADS trial garden has been starting tubers in gallon pots 3-4 weeks prior to planting date. Yes, they are kept very moist and all this stuff about not watering tubers until they sprout is is a myth.

dahlia1972

OK should I move them from their 3 inch pots, and if so, what's the smallest pot they'll survive in? I have about 50 tubers I'd like to start so I'll be buying pots in bulk. If they'll survive in the 3 inch pots I'd prefer to leave them there but if need be I'll repot them.

Teddahlia

What you call 3 inch pots are most likely what I call 4 inch pots. 16 of them fit into 16 inch square plastic flat. They are fine for small tubers. If you can find them there are larger pots that have the same dimensions as the bottoms of the 4 inch pots but are taller and wider at the top. They fit into the 16 inch flats just fine. They are nicer yet. These are all rectangular pots. In round pots, I do not know the exact sizes but the gallon size is the best. Use the smallest size according to what size is the tuber. Huge tuber takes bigger pot.

calico20hill

I say, use good sense. If the pots are dry, how are the tubers going to know it is safe to grow? Just don't drown them. Give them just enough moisture that they know they can grow roots and find more water. Plants are smart that way.

KitCMC

I also have a short season and have always started tubers early. I water, but only when the soil feels dry. I’m not sure how many plants you will have going, but I have had the best success when they are outside during the day (weather dependent). I tuck them into the garage at night. There’s no hardening off that way as they’re used to the elements. I think calico20hill has a rolling cart for this! It’s a lot of babysitting, but worth it.

I just use recycled 1 gallon nursery pots. I put about 2-3” of growing media in the bottom, place the tuber, then cover with another _2” growing media. When I plant them out, I cover a few more inches up the stem with soil, similar to planting a tomato.

PNWGal

I start all my tubers in pots inside. They go into pretty much the smallest pot they will fit into without squashing them. I use mostly 3-1/2" to 4" square pots, with 5" squares (=1/2 gallons) for the largest ones. (Bigger tubers get their root ends shortened first.) I don't have room to start anything in gallon pots. I start them out in potting soil which is damp but not really wet. Definitely cover the head ends as well as the rest. The quicker to sprout ones come up with no additional watering, but some are much slower to sprout, especially if they got a bit dry in storage. If the potting soil gets dry, I water them some, like Noni/calico20hill said. Anything that hasn't put up visible shoots after a couple of weeks definitely gets watered. Some tubers just take more water and/or time than others to get going. Of course once there are visible shoots, the pots get more water and weak soluble fertilizer. If the weather is such that the garden beds are slow to warm up, I occasionally repot into larger pots as needed to keep the plants from getting rootbound. It's important to keep them actively growing the whole time before planting out.

Darce

I grow my tubers in a 4.5 inch 15 plug tray- it works great and I only have to lift a tray not shuffle around a bunch of 4 inch pots - I can put the tray in a larger flat tray filled with water and then water from the bottom- the plants get very stout and hardy

Darce

Only very large tubers won’t work in this as it is deep and is perfect till plants get about 5-6 inches tall

KitCMC

Darce I haven’t seen this product before, but am intrigued. Do you put tubers in vertically? How hard/easy is it to pop plants out? I try to reuse plastic if possible - do you think it could be used more than once? Thanks!

Darce

I use them for all my wintersown perennials too! And this year I am going to do willow cuttings in one plug tray. They are sturdy and I definitely reuse them - I am going on my 3rd year with them (I am with you about single use plastic) I have left some out over winter with perennials in it in a DIY mini hoop house and they survived fine - I can still reuse - there was a crack or two in one tray from winter exposure but a piece of duct tape fixed it right up
I put the tubers in vertically - at a slant usually. Smaller tubers i just pop right in anyhow. The roots of both tubers and seedlings get big and strong and I usually can just pop them out in one piece using the drainage hole in the bottom

Here is a pic of them from the side so you can get an idea of dimensions

Here is link to product https://www.greenhousemegastore.com/products/sureroots-deep-cell-plug-trays?variant=42701224181959

PegMc

Darce Thanks for this share, Darce!

JessieC

Darce Those are really nice! I have noticed a difference when I use containers that are meant for seeds and cuttings. I saw a clever idea to use leftover milk containers, washed and with drainage holes added, of course. I imagine because I’m a novice, that didn’t work out well for me. The better pots have grooves and holes in the right spot for optimal drainage. I’ll check these out!

KitCMC

Darce Nice find! Thanks for sharing 😁

Darce

JessieC

I winter sow in water jugs and milk jugs- and have started some dahlias in them too - I have found for me it works best to put a CRAZY amount of drainage holes in - much more than what most people show on YouTube etc

These trays are so nice because in conjunction with this tray without holes filled with water I can just place the plug tray in and water them from the bottom pretty effortlessly

There is also this tray WITH HOLES I use to start off a bunch of tubers of the same variety
The trays are made of a super thick plastic which should last for years

Lol I promise I am not in the pay of greenhouse megastore😂🤣

PegMc

I've been waiting for these two to be large enough to snap a photo so that I could ask questions -- both were slightly eyed up when received, and something didn't look quite right with either of them, but the sprouts were too tiny to really see what was going on. Now they are. Skipley Moonglow (mold...) didn't have mold 'til this morning, but the leaves had turned black as shown. Note that there is new growth that is seemingly not affected (yet?). What has caused this and what should I do to correct the problem? Same questions for Crazy 4 Teedy's sprout? Also, I want to ask, is it a good idea or no to top off the potting soil surface with vermiculite? I'd just started doing this (the tray that these two were in), thinking it would help keep the pots from drying out quite as fast. Yes? No? What else should I be asking & needing to know? Thanks....

Teddahlia

I would cut off these sprouts and sprinkle some cinnamon on the cut and bury the the tuber eye below the soil level for the next sprouts. I sprout the first sprouts under potting soil and then(but not always) place the sprout end of the tuber above the soil level for future sprouts. I like the convenience of the eyes above soil level but the sprouts actually grow better under the potting soil. Sometimes a cutting will have white root or two when grown under the soil and this almost never happens if grown above the soil level. Obviously, since they already have roots, they root very well

JessieC

Darce Well, it’s always nice to see things that are well designed for the task. I hate to waste leftover material, but I also don’t have a ton of space indoors. I appreciate the grow shop here that has many configurations of trays, containers, domes, etc. And you can just buy one to try it out! They’re awfully helpful and pleasant too.

SGriff

i use 3 X 3 x 3 " pots for smaller tubers, and 3 x 3 x 5" deep pots for larger ones. if they are too big i cut them off to fit. usually they go in diagonally, with the crown pretty near the top of the pot. just a bit of soil needed to cover the crown, as I'll plant them out at proper depth. these small pots fit 18 to a 1020 tray and allow a good number of tubers to be started indoors in a small space.