When To Start Seeds Indoors – Includes a Chart

One of the most frequently asked questions from new gardeners is, when should I start my seed indoors? It all seems so complicated with many different types of seeds, both vegetables and flowers. This post will simplify the answer for you.

Type of Seeds

In this post I am talking about seeds that will end up going into the garden, mostly vegetables, annuals and perennials.

Seeds for houseplants can be started at any time. Most gardeners don’t grow trees and shrubs from seed so I won’t mention them except to say that they can usually be treated like perennials.

New gardeners only think about a few types of seeds. Originally, it’s mostly vegetables. With experience they might add some common annuals, and then some perennials. The reality is that there are thousands of different garden plants you could grow from seed. There is no simple answer to the question, when do you start seeds indoors? Any rule I give you is not going to be right all of the time.

In this post I will give you several answers. If you are new to growing from seed, you may want to use a simple rule. As you gain experience you will fine tune that for your own growing conditions, your goals and for the type of seed you are trying to grow.

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A Simple Seed Starting Rule

Start seed 6 weeks before your last frost date. For annuals and perennials you can extend this to 8 weeks.

Most seed germinates in 2 weeks, so this gives you 4-6 weeks of actual growing time before they go outside and that is adequate time for seedlings to put on enough growth to be outside.

A Better….Simple Seed Starting Rule

Follow the instructions on the package. This is simple and it works unless you collected the seed yourself and don’t have a package. In that case try to find the seed in an online seed catalog. Many of the better seed sources provide germination information.

This will again be based on the last frost date.

Why Use The Last Frost Date?

Most seed that is started indoors can’t take frost, so you can’t take them outside until all danger of frost is gone.

Rather than give you a calendar date, seed packages give you a time before last frost. This is then valid in any gardening zone.

How Do I Find My Last Frost Date?

You can ask an experienced local gardener, or your local Master Gardener group – they will know the date. You can also Google your area. There is lots of online help.

The problem with online help is that it’s usually based on data from large cities. If you are in a small town you won’t find a date, and the date for a large town is usually wrong for you because large town generate their own heat, making the last frost date earlier than in nearby smaller towns or rural areas.

Keep in mind that this date has been moving with climate change. Historically my date, for zone 5, was May 24. That has not been a valid date for many years. It’s now closer to May 8.

Use A Seed Planting Chart

A planting chart, also called a seeding calendar, is handy for vegetables and common flowers and I’ve provided some charts at the end of this post.

If your seed is not on the list, the list will still give you an approximate value if you can find a similar plant on the list.

Starting Annuals From Seed

You could start seed for annuals at any time. The above 6 week rule works and will give you plants in the garden. The problem with this is that most people want their annuals to flower soon after planting so they get a long season of bloom. To achieve this, you have to start annuals quite early, so that they are large enough to flower once planted in the garden.

Seed packages usually provide a “date to flowering” time on the package. You can use this to back calculate a seeding date that will give you flowers when you want them.

In order to get early flowering, you usually have to keep annuals indoors for quite some time. Make sure you have space and light for this.

Starting Perennials From Seed

Perennials rarely flower the first year from seed. Some will flower the second year, and some, like peonies, will take 5 years before they flower. For this reason it is less important to start perennials early. Many can be started using the simple ‘6 weeks before last frost date’ rule.

Some perennial seed can take a couple of months to germinate so they are best started early so you have a good sized plant by the time it goes outside.

A great way to start perennials is with winter sowing, which eliminates the need to get the seeding date right. Using this method, nature takes care of it for you.

If this video does not play, try this link: https://youtu.be/SO_KKbGYTEM

Adjusting The Date for Seeding

So far in this post I have given you some simple rules to determine the seed starting date. As you gain more experience you will fine tune this date based on a number of factors.

• Available lighting
• Pot size and available space
• Cheating nature
• Getting an earlier harvest
• Using a heating mat

Lets have a look at each of these in detail.

Available Lighting For Seed Starting

Many people start seeds next to windows, or under shop lights. These provide lots of light for small seedlings, but as the plants grow then need more light. If you can’t provide the light, growth slows down and they get leggy.

If you can provide good lighting you can start seeds earlier and produce larger transplants. This will speed things up once in the garden. But if you can’t provide good lighting, it is better to start later, and use smaller transplants. Many people can’t wait for spring and start plants way too early, and end up with weak, sickly plants.

Pot Size and Available Space

There is a big trend towards using small pots to start seeds, including things like eggshells, single-serve yogurt containers, Jiffy pots and toilet paper rolls. The plastic six-packs used by commercial growers are also popular. These can all be used to start seed, but the plants quickly outgrow their space. Before roots start to get root bound, you need to move them to larger pots.

Larger pots means that you need a lot more space with good lighting. It also means more soilless mix, and more watering. Are you prepared to do this? If not, it is better to delay your seed starting so that the seedlings don’t outgrow their smaller pots.

Larger pots can grow some nice large vegetables. I’ve had tomato plants flower in my sun room, very early in spring. But you need large pots and smaller varieties to make this viable.

Cheating Nature

This applies mostly to vegetables, but you can also get some perennials flowering the first year by starting very early.

In cold climates you want to do everything you can to have an early harvest, especially for things like tomatoes that take a long time to produce the first fruit and produce until frost. You can hope for an early spring and seed several weeks earlier than suggested. If you get lucky, they go outside earlier than usual. If you get a late spring, you have to contend with the plants indoors longer than ideal.

Or you plant them outside early and cover them if frost shows its ugly head.

Some growers will split their seed. Some early and some later. They can then use the best seedlings based on the weather gods.

Getting An Earlier Harvest

This applies mostly to vegetables. Plants need to be a certain size before they start producing food. Creating larger transplants, will give you an earlier harvest. With tomatoes in zone 5, you can be eating fruit 2 weeks earlier with large transplants.

Cucumbers are normally seeded directly in the garden, but seed won’t germinate until the soil is warm enough, giving you a late start. You can get a much earlier harvest by starting plants indoors. Ignore common advice that cucumbers don’t transplant well. Just do it gently and they will be fine.

Some people even start root crops like beets and carrots indoors and then transplant outside when the weather permits.

Using a Heating Mat For Seed Starting

In most cases a heating mat is not required, but they can increase the temperature for the seed. Most seed will germinate faster with a bit of heat, but some seed will stop germinating if they get too warm.

In a cold basement, a heating mat can speed up germination by a week or two, which changes your start time.

Always remove the seedlings from the heating mat once they have germinated. Seedlings grow better below room temperature.

Don’t Forget Stratification

Stratification is a technique were seeds are exposed to cold for a period of time to help them germinate. If seeds need to be stratified you have to start them earlier so that they germinate when you want to start taking care of seedlings. Vegetables and most annuals do not need stratification, but many perennials and trees do.

Seed Starting Myths

There is a lot of good information online, but some of it is just plain wrong. Here is a video showing some common myths that can cause you problems.

If you have trouble viewing this video, use this link: https://youtu.be/b9e_tT_Xd8s

Seed Starting Chart

Many online sites provide seed starting calendars which give you the best date to start seeds. The problem with these is that they are rarely based on your location. Some are based on a hardiness zone, and others use a region like a state or province. These are approximately correct, but most such regions have different gardening zones.

It is much better to create your own calendar by using the last frost date and working back to get the seed starting date.

Here are some charts you can use. With experience you will modify the start date based on your personal situation and goals.

When to Start Vegetable Seed

When to Start Annual Flower Seed

When to Start Perennial and Biennial Seed