Review: Pro-Mix Seed Starting Mixes for Growing Tomato Seeds

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Pro-Mix® is the name brand of a series of professional-grade growing mediums. Both home gardeners and commercial growers give it a passionate thumbs-up for tomato seed starting. Pro-Mix is soilless. Its main ingredients are sphagnum peat moss, perlite or vermiculite (depending on the blend), starter nutrients, limestone, and a wetting agent.

What’s the big deal about Pro-Mix?

While Pro-Mix can be a bit on the expensive side, gardeners like it because it’s sterile, reliable, and has a fine consistency. When they use Pro-Mix, their seeds have a high germination rate. Tomato seedlings grow healthy and strong. The sphagnum peat base and perlite/vermiculite allow excellent water retention along with air pockets for circulation. For gardening satisfaction, it’s worth the extra nickels and dimes.

(Buy Pro-Mix here.)

Which Pro-Mix should I choose?

Pro-Mix with Tomato Dirt

While Pro-Mix nearly always gets an “atta-boy” for results, there are other variables that can make the tomato gardener wonder whether or not to choose this product for seed starting. First, there are a large number of products under the “Pro-Mix” brand. It’s confusing. How can you know which one to use?

Short answer: Pro-Mix has two different product series – a professional Pro-Mix series and a consumer Pro-Mix series. There are various formulas within each series. (Check out the list below for a summary.)

The professional series products contain a growth enhancer (called Mycorise®) and are packaged in high quantities (3 cubic feet, 3.8 cubic feet, 55 cubic feet, and 70 cubic feet). Even so, commercial growers are not the only ones who use the professional series products. Home gardeners who grow lots of their own seedlings also use the professional series. They keep leftovers to use year-to-year or split the amounts with other gardeners.

As far as the consumer mix series goes, just one (the Ultimate Seeding Mix) also contains growth enhancer Mycorise. The advantage of the consumer mix series, of course, is that packaging sizes (8 quarts, 16 quarts, 1 cubic foot, and 1.8 cubic feet) are much more manageable for the home gardener.

There are different Pro-Mix formulas available in each series. Don’t let that confuse you too much. Pro-Mix products are formulated for different functions like germination, potting, containers, indoor cultivation, and outdoor cultivation. Obviously, if you’re going to use Pro-Mix to start seeds, you should choose a seeding mix or a potting and seeding mix.

(Here's where you can find Pro-Mix online.)

Professional Pro-Mix Series (for seed starting)

Pro-Mix BX: a general purpose peat/perlite/vermiculite growing medium
Pro-Mix HP: a high porosity peat/perlite-based growing medium
Pro-Mix PGX: a plug and germination growing medium

Consumer Pro-Mix Series (for seed starting)

Pro-Mix Ultimate Seeding Mix: peat-based growing mix for germinating seeds
Pro-Mix for Potting and Seeding: peat-based growing mix potting and seeding and potting
Pro-Mix for Potting: peat-based, multi-use mix suitable for seeding, re-potting, indoor, and outdoor use

What are other advantages and disadvantages to Pro-Mix?

The advantages of using a Pro-Mix product to start tomato seeds

Sterility. Pro-Mix is a soil-less medium. It’s a sterile environment with no bacteria or fungi to kill seeds or seedlings. That means you lose fewer seedlings to damping-off during the starting process. Plus, the seedlings you grow are stronger since they don’t have to fight as many infections.
Contents. All formulas are sphagnum peat moss-based. Peat is known for its ability to retain water. It’s also got anti-bacterial qualities. In addition, Pro-Mix formulas contain perlite or vermiculite (also good at keeping a nice moisture balance), a bit of limestone (for pH adjustment), a wetting agent, and some trace starter nutrients (but not too many.)
Quality. Pro-Mix has a reputation for evenness and consistency. The peat moss is milled to very fine texture. That makes it a very good environment for seeds to germinate.
pH. When it comes to tomatoes, Pro-Mix has a good pH balance. It’s recommended for plants requiring a growing pH between 5.5-7.0. Tomatoes grow best in a pH of 6.0-7.0.
Minimal fertilizer. Pro-Mix contains traces of extra nutrients. This is a plus because new seedlings rely on nutrients provided by the seed while they germinate and take root. Excess fertilizing at this stage can make tomato plants leggy or weak. Pro-Mix encourages you to put a fertilization schedule into place when seedlings are 3-4 weeks old.
Growth booster. Many Pro-Mix products contain a growth enhancer, Mycorise, which gardeners insist makes a difference for their plants.

The disadvantages of using a Pro-Mix product to start tomato seeds

Availability. Pro-Mix can be hard to find locally. You made need to call several retail outlets or order it online.
Cost. Pro-Mix is not cheap. However, to be fair, gardeners say that the excellent results they get with it offset the extra cost, since they lose fewer seedlings and have stronger plants to set out in the garden, which often produce higher yields.
Packaging. If you choose to use one of the professional series formulas, you must buy Pro-Mix in bulk. This is useful if you start hundreds of plants, or have space to save and use the leftovers from year to year, or share the cost with other gardeners. But if you’ve got limited storage, or if you don’t have a way to seal Pro-Mix to keep it clean until next year, think twice. Solve this dilemma by buying a Pro-Mix commercial formula, which is packaged in smaller amounts.
Time. As with all seed starting mediums, you must add warm water to Pro-Mix before using it. Gardeners complain that Pro-Mix is especially tightly compressed. It takes time to break it up to get an even consistency before you plant seeds.
Maintenance. Some gardeners struggle with keeping Pro-Mix moist after planting. They say it can be difficult to re-wet. However, this most often happens when a gardener hasn’t been checking seedling trays daily to monitor moisture. Seed starting mix of any kind can dry out fast if it is not kept moist.

Bottom line: if you’re starting tomato seeds, a Pro-Mix product is a high-quality, reliable bet. Read the labels carefully. Choose from these Pro-Mix products which are most suitable for seed starting. Either the professional or consumer series will work – that choice depends on how much of the mix you want to buy (or store).

(Buy Pro-Mix here.)

All Pro-Mix products are manufactured by Premier Horticulture.

Helpful tips when using Pro-Mix

  • Pro-Mix has a reputation for being compressed and hard to work with. Transfer Pro-Mix to large Rubbermaid container or wheelbarrow and use a 3-tine claw or hand tool to break up clumps. Alternatively, add water to Pro-Mix, cover it, and let moisture soak into the mix before mixing.
  • Turn Pro-Mix with small shovel or miniature spade (rather than a trowel).
  • Stretch Pro-Mix, lighten the texture, and help it be more water absorbent by adding either 7-10% playground sand or 20-25% additional perlite.
  • After planting tomato seeds in moistened Pro-Mix, cover them with a sprinkle of dry mix for added anti-bacterial protection.

Is it really so hard to find Pro-Mix?

You can order it online. Alternatively, readers have found Pro-Mix at these distributors:

  • Home Depot
  • Canadian Tire
  • Local nurseries
  • Rona
  • Lowe’s

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