Custom substrate recipes: how to brief your supplier clearly

A request for a custom substrate is most useful when it describes the job the mix must do, not just its ingredients. A mix that works in a deep nursery pot may behave differently in a shallow tray, even when the crop is the same.

Send your current datasheet if you have one, then explain what you want to keep or change. The details below give a supplier enough to discuss a workable specification rather than guess from a product name.

Start with the crop, container and growing method

Name the crop, its stage of growth and how long you expect it to remain in the medium. Seed germination, propagation and potting on place different demands on particle size, moisture retention and air space. If you grow several crops in one mix, say which crop is least tolerant of the compromise.

Give the tray cell or pot dimensions, not just a description such as “small pot”. Container depth affects how a medium drains and how much water remains near the base after irrigation. Also describe whether you fill by hand or machine, since a screening that fills one system neatly may bridge or settle in another.

• Growing system. State whether the crop is raised in plugs, trays, pots or another container, and describe the irrigation method.
• Crop cycle. Include the expected time in the container and whether plants will be transplanted, sold or held on in the same mix.
• Current difficulty. Explain what prompted the change, such as uneven filling, a mix that stays wet too long, or a need to adjust the feeding programme.

These observations help turn a broad request into a testable brief. They also give both sides a way to judge a trial against the mix already in use.

Send the current datasheet and define the targets

The datasheet for your present substrate is a useful starting point, particularly if it lists raw materials, screening, pH, electrical conductivity and fertiliser. Add your own measurements and notes from use. A printed specification shows what was supplied, while your observations show how it performed under your water, irrigation and feeding conditions.

Give target pH and EC as ranges and say when you want them checked. Include the test method where known, because results obtained by different methods are not always directly comparable. For context, SOLVIKA publishes peat pH measured to EN 13037 and EC measured to EN 13038, and product-page figures are typical grade values rather than guarantees for an individual batch.

• Must keep. Identify properties of your current mix that work well, such as its filling behaviour or response to irrigation.
• Must change. Separate essential requirements from preferences. If a particular pH range or ingredient is non-negotiable, make that clear.
• Trial measure. Decide what you will record during testing, such as uniformity of filling, watering frequency, root development and measured pH and EC.

If you need an analysis for a particular batch rather than typical grade figures, ask for that explicitly. A precise testing requirement is easier to discuss before the recipe and order are agreed.

Specify the structure, additives and fertiliser

Describe the structure you need in practical terms, then give a preferred screening if you know it. Finer material can help fill small cells consistently, while a coarser fraction is often chosen where maintaining air space matters over a longer crop cycle. Ask how a proposed screening will behave in your own filling and irrigation setup rather than relying on its name alone.

State which ingredients you want included or excluded. SOLVIKA can blend peat categories with perlite, clay, wood fibre, limestone, wetting agent and a choice of fertilisers for an individual recipe. Its substrate ranges also provide useful starting points if you want to compare a custom brief with an existing type of mix.

Be especially clear about fertiliser. Do you want a starter charge in the bag, or will you dose all nutrients through your own programme? SOLVIKA's pH-adjusted base substrates contain a wetting agent but no fertiliser. For example, code 220LV is a white peat base substrate screened to 0-20 mm and adjusted to pH 5.5 to 6.5.

If you request wood fibre or perlite, explain the reason as well as the intended proportion. Changes to ingredients can alter watering and feeding practice, so plan to trial the proposed mix in your own conditions before replacing a working recipe.

Include packaging, volume and delivery details

Packaging belongs in the technical brief because it affects handling at your site. Say whether the product will feed an automated line, be moved by forklift or be opened beside a potting bench. Include any limits imposed by your storage area or the equipment used to empty the packs.

Specify the pack size you prefer, your expected volume per order and your likely ordering pattern. Available sizes vary by product, so do not assume that a format used for one grade is available for a different recipe. SOLVIKA's minimum order is one full load, shared by up to 3 products, and each product starts at 10 pallets of 50 L or 70 L bags, 8 pallets of 250 L bags or 6 pallets of big bales.

• Quantity. Give the volume needed for a trial and the expected volume for regular orders. Keep these figures separate.
• Destination. Provide the destination country and either the port of discharge or the full delivery address.
• Timing. Give your first required delivery date and any seasonal peaks. Order preparation typically takes 2 to 4 weeks, and 4 to 5 weeks in spring and autumn, depending also on size and product, so ask for a confirmed date.
• Delivery term. State your preferred Incoterm if you have one. Containers ship FCA, FOB, CFR or CIF from Klaipeda or Riga. Trucks go EXW or DAP, and DAP is only for delivery within the EU.

Agree how the recipe will be checked and repeated

A custom recipe is only useful if the agreed specification is clear enough to repeat. Record the peat types, screening, additives, fertiliser, pH and EC targets, packaging and any agreed test methods in one document. If a requirement changes after a trial, update that document rather than relying on a description such as “the same mix, but lighter”.

SOLVIKA produces substrates on computer-controlled mixing lines that follow the agreed recipe for each order. Peat is a natural material, though, and its figures are typical values rather than a guarantee for each batch. Define what you will check on receipt and during growing, and ask whether you need a batch analysis for a particular order.

Keep notes from a small-scale trial alongside the agreed recipe. Record how the medium fills, wets and drains, then follow pH, EC and crop response under your normal irrigation and feeding programme. When you send those observations back, distinguish a change you want in the substrate from a change you can make in management.

Before repeat ordering, confirm the final specification, pack format and product identification with the supplier. That gives purchasing, production and the growing team the same reference when the next order is placed.

Frequently asked questions

Send your crop, container size, current datasheet, target pH and EC, ingredients, fertiliser requirements, packaging, volume and destination through the contact form. For a delivered price, also give your preferred delivery term.