//This should be in your Mod main class under the @Init method.
//Note that public static Block/Item should be in your @Instance method.
		public static Block Rubarb;
			Rubarb = (new Rubarb(448)).setUnlocalizedName("Rubarb");
			GameRegistry.registerBlock(Rubarb, "Rubarb");
			LanguageRegistry.addName(Rubarb, "Rubarb");

//Edit name,ID,the BlockId's to whatever your want.

		public static Item rubarb;
			rubarb = (new ItemSeedFood(452, 4, 0.3F, Rubarb.blockID, Block.tilledField.blockID)).setUnlocalizedName("mystique:Rubarb");
			GameRegistry.registerItem(rubarb, "rubarb");
			LanguageRegistry.addName(rubarb, "Rubarb");

//Here is the Block class for the crop.
//Change package and names to what fits your mod.Also change or add imports if needed!

package erikstutorials;

import net.minecraft.block.BlockCrops;
import net.minecraft.client.renderer.texture.IconRegister;
import net.minecraft.item.Item;
import net.minecraft.item.ItemStack;
import net.minecraft.util.Icon;
import net.minecraft.world.World;
import cpw.mods.fml.relauncher.Side;
import cpw.mods.fml.relauncher.SideOnly;

public class Rubarb extends BlockCrops
{
    @SideOnly(Side.CLIENT)
    private Icon[] iconArray;

    public Rubarb(int par1)
    {
        super(par1);
    }

    @SideOnly(Side.CLIENT)

    /**
     * From the specified side and block metadata retrieves the blocks texture. Args: side, metadata
     */
    public Icon getBlockTextureFromSideAndMetadata(int par1, int par2)
    {
        if (par2 < 7)
        {
            if (par2 == 6)
            {
                par2 = 5;
            }

            return this.iconArray[par2 >> 1];
        }
        else
        {
            return this.iconArray[3];
        }
    }

    /**
     * Generate a seed ItemStack for this crop.
     */
    protected int getSeedItem()
    {
        return Mod_Main.rubarb.itemID;
    }

    /**
     * Generate a crop produce ItemStack for this crop.
     */
    protected int getCropItem()
    {
        return Mod_Main.rubarb.itemID;
    }

    @SideOnly(Side.CLIENT)

    /**
     * When this method is called, your block should register all the icons it needs with the given IconRegister. This
     * is the only chance you get to register icons.
     */
    public void registerIcons(IconRegister par1IconRegister)
    {
        this.iconArray = new Icon[4];

        for (int i = 0; i < this.iconArray.length; ++i)
        {
            this.iconArray[i] = par1IconRegister.registerIcon("carrots_" + i);
        }
    }
}